EO Topics on Climate Change
EO (Earth Observation) Topics on Climate Change
Since the start of the space age, Earth observation is providing its share of evidence for a better perception and understanding of our Earth System and its response to natural or human-induced changes.
Earth is a complex, dynamic system we do not yet fully understand. The Earth system comprises diverse components that interact in complex ways. We need to understand the Earth's atmosphere, lithosphere, hydrosphere, cryosphere, and biosphere as a single connected system. Our planet is changing on all spatial and temporal scales.
Over the years, the entire Earth Observation community, the space agencies as well as other governmental bodies, and many international organizations (UN, etc.) are cooperating on a global scale to come to grips with the modeling of the Earth system, including a continuous process of re-assessment and improvement of these models. The goal is to provide scientific evidence to help guide society onto a sustainable pathway during rapid global change.
In the second decade of the 21st century, there is alarming evidence that important tipping points, leading to irreversible changes in major ecosystems and the planetary climate system, may already have been reached or passed. Ecosystems as diverse as the Amazon rainforest and the Arctic tundra, may be approaching thresholds of dramatic change through warming and drying. Mountain glaciers are in alarming retreat and the downstream effects of reduced water supply in the driest months will have repercussions that transcend generations. 1)
Table 1: Overview of some major international bodies involved in global-change research programs 2)
The UN Framework Convention on Climate Change (UNFCCC) is an intergovernmental treaty developed to address the problem of climate change. The Convention, which sets out an agreed framework for dealing with the issue, was negotiated from February 1991 to May 1992 and opened for signature at the June 1992 UN Conference on Environment and Development (UNCED) — also known as the Rio Earth Summit. The UNFCCC entered into force on 21 March 1994, ninety days after the 50th country's ratification had been received. By December 2007, the convention had been ratified by 192 countries. 3)
In the meantime, there were many UN conferences on Climate Change, starting with the UN climate conference in Kyoto, Japan, in December 1997. The Kyoto Protocol set standards for certain industrialized countries. Those targets expired in 2012.
Meanwhile, greenhouse gas emissions from both developed and developing countries have been increasing rapidly. Even today, those nations with the highest percentage of environment pollution, are not willing to enforce stricter environmental standards in their countries in order to protect their global business interests. It's a vicious cycle between these national interests and the deteriorating environment, resulting in more frequent and violent catastrophes on a global scale. All people on Earth are effected, even those who abide by their strict environmental rules.
The short descriptions in the following chapters are presented in reverse order on some topics of climate change to give the reader community an overview of research results in this wide field of global climate and environmental change.
NASA Study of the Causes of Earth's Recent Record Carbon Dioxide Spike
• October 12, 2017: A new NASA study provides spaceborne evidence that Earth's tropical regions were the cause of the largest annual increases in atmospheric carbon dioxide (CO2) concentration seen in at least 2,000 years. 4)
Scientists suspected the 2015-2016 El Niño — one of the largest on record — was responsible, but exactly how has been a subject of ongoing research. Analyzing the first 28 months of data from NASA's OCO-2 (Orbiting Carbon Observatory-2) satellite, researchers conclude impacts of El Niño-related heat and drought occurring in tropical regions of South America, Africa and Indonesia were responsible for the record spike in global carbon dioxide. The findings are published in the journal Science on 13 Oct. 2017 as part of a collection of five research papers based on OCO-2 data. 5) 6) 7) 8) 9) 10) 11)
Figure 1: The last El Niño in 2015-16 impacted the amount of carbon dioxide that Earth's tropical regions released into the atmosphere, leading to Earth's recent record spike in atmospheric carbon dioxide. The effects of the El Niño were different in each region (image credit: NASA-JPL/Caltech)
"These three tropical regions released 2.5 gigatons more carbon into the atmosphere than they did in 2011," said Junjie Liu of NASA/JPL in Pasadena, California, who is lead author of the study. "Our analysis shows this extra carbon dioxide explains the difference in atmospheric carbon dioxide growth rates between 2011 and the peak years of 2015-2016. OCO-2 data allowed us to quantify how the net exchange of carbon between land and atmosphere in individual regions is affected during El Niño years." A gigaton (Gt = 109 tons) is a billion tons.
In 2015 and 2016, OCO-2 recorded atmospheric carbon dioxide increases that were 50 percent larger than the average increase seen in recent years preceding these observations. These measurements are consistent with those made by NOAA (National Oceanic and Atmospheric Administration). That increase was about 3 parts per million of carbon dioxide per year — or 6.3 gigatons of carbon. In recent years, the average annual increase has been closer to 2 parts per million of carbon dioxide per year — or 4 gigatons of carbon. These record increases occurred even though emissions from human activities in 2015-2016 are estimated to have remained roughly the same as they were prior to the El Niño, which is a cyclical warming pattern of ocean circulation in the central and eastern tropical Pacific Ocean that can affect weather worldwide.
Using OCO-2 data, Liu's team analyzed how Earth's land areas contributed to the record atmospheric carbon dioxide concentration increases. They found the total amount of carbon released to the atmosphere from all land areas increased by 3 gigatons in 2015, due to the El Niño. About 80 percent of that amount — or 2.5 gigatons of carbon — came from natural processes occurring in tropical forests in South America, Africa and Indonesia, with each region contributing roughly the same amount.
The team compared the 2015 findings to those from a reference year — 2011 — using carbon dioxide data from the GOSAT (Greenhouse Gases Observing Satellite) mission of JAXA (Japan Aerospace Exploration Agency). In 2011, weather in the three tropical regions was normal and the amount of carbon absorbed and released by them was in balance.
"Understanding how the carbon cycle in these regions responded to El Niño will enable scientists to improve carbon cycle models, which should lead to improved predictions of how our planet may respond to similar conditions in the future," said OCO-2 Deputy Project Scientist Annmarie Eldering of JPL. "The team's findings imply that if future climate brings more or longer droughts, as the last El Niño did, more carbon dioxide may remain in the atmosphere, leading to a tendency to further warm Earth."
While the three tropical regions each released roughly the same amount of carbon dioxide into the atmosphere, the team found that temperature and rainfall changes influenced by the El Niño were different in each region, and the natural carbon cycle responded differently. Liu combined OCO-2 data with other satellite data to understand details of the natural processes causing each tropical region's response.
In eastern and southeastern tropical South America, including the Amazon rainforest, severe drought spurred by El Niño made 2015 the driest year in the past 30 years. Temperatures also were higher than normal. These drier and hotter conditions stressed vegetation and reduced photosynthesis, meaning trees and plants absorbed less carbon from the atmosphere. The effect was to increase the net amount of carbon released into the atmosphere.
In contrast, rainfall in tropical Africa was at normal levels, based on precipitation analysis that combined satellite measurements and rain gauge data, but ecosystems endured hotter-than-normal temperatures. Dead trees and plants decomposed more, resulting in more carbon being released into the atmosphere. Meanwhile, tropical Asia had the second-driest year in the past 30 years. Its increased carbon release, primarily from Indonesia, was mainly due to increased peat and forest fires — also measured by satellite instruments.
"We knew El Niños were one factor in these variations, but until now we didn't understand, at the scale of these regions, what the most important processes were," said Eldering. "OCO-2's geographic coverage and data density are allowing us to study each region separately."
Scott Denning, professor of atmospheric science at Colorado State University in Fort Collins and an OCO-2 science team member who was not part of this study, noted that while scientists have known for decades that El Niño influences the productivity of tropical forests and, therefore, the forests' net contributions to atmospheric carbon dioxide, researchers have had very few direct observations of the effects. "OCO-2 has given us two revolutionary new ways to understand the effects of drought and heat on tropical forests: directly measuring carbon dioxide over these regions thousands of times a day; and sensing the rate of photosynthesis by detecting fluorescence from chlorophyll in the trees themselves," said Denning. "We can use these data to test our understanding of whether the response of tropical forests is likely to make climate change worse or not."
The concentration of carbon dioxide in Earth's atmosphere is constantly changing. It changes from season to season as plants grow and die, with higher concentrations in the winter and lower amounts in the summer. Annually averaged atmospheric carbon dioxide concentrations have generally increased year over year since the early 1800s — the start of the widespread Industrial Revolution. Before then, Earth's atmosphere naturally contained about 595 gigatons of carbon in the form of carbon dioxide. Currently, that number is 850 gigatons.
The annual increase in atmospheric carbon dioxide levels and the magnitude of the seasonal cycle are determined by a delicate balance between Earth's atmosphere, ocean and land. Each year, the ocean, plants and trees take up and release carbon dioxide. The amount of carbon released into the atmosphere as a result of human activities also changes each year. On average, Earth's land and ocean remove about half the carbon dioxide released from human emissions, with the other half leading to increasing atmospheric concentrations. While natural processes are responsible for the exchange of carbon dioxide between the atmosphere, ocean and land, each year is different. In some years, natural processes remove as little as 20 percent of human emissions, while in other years they scrub as much as 80 percent.
OCO-2, launched in 2014, gathers global measurements of atmospheric carbon dioxide with the resolution, precision and coverage needed to understand how this important greenhouse gas — the principal human-produced driver of climate change — moves through the Earth system at regional scales, and how it changes over time. From its vantage point in space, OCO-2 is able to make roughly 100,000 measurements of atmospheric carbon dioxide each day, around the world.
Institutions involved in the Liu study include JPL; NCAR (National Center for Atmospheric Research) in Boulder, Colorado; the University of Toronto; Colorado State University; Caltech in Pasadena, California; and Arizona State University in Tempe, AZ.
Figure 2: The Science special collection of OCO-2-based papers give an unprecedented view from space of how carbon dioxide emissions vary within individual cities such as Los Angeles and its surroundings, shown here. Concentrations vary from more than 400 parts per million (red) over the city, foreground, to the high 300s (green) over the desert, background (image credit: NASA/JPL-Caltech/Google Earth) 12)
Monitoring of Groundwater Recovery in Silicon Valley
October 3, 2017: A NASA/university study finds aggressive conservation helped region's aquifer rebound quickly from one of the worst droughts in California history. Underground water reserves in California's Silicon Valley rebounded quickly from the state's recent severe drought, demonstrating the success of aggressive conservation measures, according to a new space-based study by NASA and university scientists. 13)
Using satellite data from COSMO-SkyMed, a constellation of four Italian Space Agency (Agenzia Spaziale Italiana, or ASI) satellites, a research team led by Estelle Chaussard at the University at Buffalo in New York, and including scientists from NASA/JPL (Jet Propulsion Laboratory) in Pasadena, California, used a technique called SAR (Synthetic Aperture Radar) interferometry to monitor the entire Santa Clara Valley aquifer near San Jose from 2011 to 2017. This type of radar can capture the subtle up-and-down movements of Earth's surface of just minute fractions, a few millimeters, that occur when water levels rise or fall underground. The scientists used hundreds of radar images obtained under a license from ASI to calculate how much the land surface elevation changed over time. The measurements show the aquifer began to rebound in late 2014, when the drought was still going strong, and that groundwater levels had returned to pre-drought levels by 2017, thanks to conservation measures that intensified in 2014, and heavy winter rains in 2016.
During the 2012-15 drought, the Santa Clara Valley Water District employed an array of conservation measures. These included restricting sprinkler use and asking customers to take shorter showers and convert lawns and pools into less-thirsty landscapes. The district also imported water from outside the region.
Chaussard says the actions may have helped stave off irreversible damage to the aquifer, which measures about 550 km2 and lies beneath a highly urbanized area. She explains when groundwater levels reach a record low, the porous sands and clays in which the reserves reside can dry up so much that the clays don't retain water anymore. The new study shows that thanks to the intensive water management efforts, this did not happen in the Santa Clara Valley.
Chaussard says the aquifer monitoring method her team used can work anywhere where there are soft-rock aquifer systems and where synthetic aperture radar satellite data are available, including in developing nations with few resources for monitoring. - "We wanted to see if we could use a remote sensing method that doesn't require ground monitoring to understand how our aquifers are responding to a changing climate and human activity," she says. "Our study further demonstrates the utility of SAR interferometry, which scientists also use to measure surface deformation related to volcanoes and earthquakes, for tracking ground deformation associated with changes in groundwater levels."
Figure 3: Ground motion in California's Santa Clara Valley from 2011 to 2015 as measured by ASI's Cosmo-SkyMed SAR constellation. Colors denote the speed of ground motion (blues indicate subsidence/sinking and reds indicate uplift). The image contains modified COSMO-SkyMed data (image credit: ASI/University at Buffalo/NASA-JPL/Caltech/Google Earth/U of Basilicata)
"This study further demonstrates a complementary method, in addition to traditional ground-based measurements, for water management districts to monitor ground deformation," added JPL co-author Pietro Milillo. "The technique marks an improvement over traditional methods because it allows scientists to gauge changes in ground deformation across a large region with unprecedented frequency." He said the COSMO-SkyMed satellites provided information for the aquifer as often as once a day.
Underground stockpiles of water — housed in layers of porous rock called aquifers — are one of the world's most important sources of drinking water. Some 2.5 billion people across the globe rely on aquifers for water, and many of these repositories are being drained more quickly than they can be refilled, according to the United Nations Educational, Scientific and Cultural Organization.
Yet keeping tabs on these precious reserves is expensive, says Chaussard. "To monitor aquifers, you need a lot of measurements in both space and time," she says. "Sampling water levels at wells may give you a continuous time series, but only if they are constantly monitored, and automated monitoring may not be common. Also, even a high density of wells may not adequately capture basin-wide spatial patterns of water storage, which is key to understanding processes at stake."
The methods employed in this study provide a more complete picture of how an aquifer responds during a drought and how water conservation methods can have a real and positive impact on sustaining the health and viability of pumped groundwater aquifers. The satellite radar imagery not only fills in data gaps between wells, but provides valuable insights into how aquifers are responding beyond the edges of monitoring well networks so that water agencies can more effectively manage their precious resources.
The upcoming NASA-ISRO (Indian Space Research Organization) Synthetic Aperture Radar (NISAR) satellite mission, planned for launch in 2021, will systematically collect radar imagery over nearly every aquifer in the world, improving our understanding of valuable groundwater resources and our ability to better manage them. In addition to tracking groundwater use in urban settings, NISAR will be able to measure surface motion associated with groundwater pumping and natural recharge in rural communities, in areas with extensive agriculture, and in regions with extensive vegetation, conditions that are typically more challenging.
The research was published Sept. 25 in the Journal of Geophysical Research - Solid Earth. Other participating institutions include the University of California, Berkeley; Purdue University, West Lafayette, Indiana; and the Santa Clara Valley Water District. 14)
Global patterns of drought recovery
September 13, 2017: As global temperatures continue to rise, the prevailing wisdom in the climate science community is that droughts will grow more frequent and more extreme in the 21st century. Though temperatures were already rising in the 20th century, the global trend in drought length and severity was ambiguous, with no clear pattern. However, the impacts of droughts was less ambiguous, particularly in recent decades. 15)
In a study published in August 2017 in the journal Nature, researchers from 17 institutions found that more of Earth's land surface is now being affected by drought and ecosystems are taking longer to recover from dry spells. Recovery is particularly worse in the tropics and at high latitudes, two areas that are already pretty vulnerable to global change. 16)
The map of Figure is based on data from that study, which was led by Christopher Schwalm of WHRC (Woods Hole Research Center). It depicts the average length of time that it took for vegetation to recover from droughts that occurred between 2000 and 2010. The darkest colors mark the areas with the longest drought recovery time. Land areas colored light gray were covered by ice or sand (deserts).
Up until now, most assessments of drought and recovery have focused on the hydrology; that is, has new rain and snowfall made up for the deficit of water in rivers, lakes, and soils? In this new study, researchers focused on the health and resilience of the trees and other plants because full reservoirs and streams do not necessarily mean that vegetation has recovered.
The research team combined observations from the MODIS (Moderate Resolution Imaging Spectroradiometer) on NASA's Terra satellite, ground measurements, and computer models to assess changes in drought. In particular, they measured changes in GPP (Gross Primary Productivity), or how well plants are consuming and storing carbon dioxide through photosynthesis. As the analysis showed, plants in many regions are taking longer to recover from drought, often because weather is more extreme (usually hotter) than in the past.
If the time between droughts grows shorter (as predicted) and the time to recover from them keeps growing longer, some ecosystems could reach a tipping point and change permanently. This could affect how much carbon dioxide is stored on land in trees and other vegetation (the land "carbon sink"). If less carbon is being captured and stored, then more of what humans produce would remain in the atmosphere, creating a feedback loop that amplifies the warming that leads to more drought.
"The most important implication of our study," said Schwalm, "is that under business-as-usual emissions of greenhouse gases, the time between drought events will likely become shorter than the time needed for recovery."
"Using the vantage point of space, we can see all of Earth's forests and other ecosystems getting hit repeatedly and increasingly by droughts," added co-author Josh Fisher of NASA's Jet Propulsion Laboratory. "Some of these ecosystems recover, but, with increasing frequency, others do not."
Figure 4: Recovery time by grid cell across all combinations of GPP and integration time. White areas are water, barren, or did not experience any relevant drought events (NASA Earth Observatory, image by Jesse Allen, using data provided by Christopher Schwalm (WHRC). Story by Michael Carlowicz, with reporting from JPL and WHRC)
Researchers find direct evidence of sea level 'fingerprints'
September 7, 2017: Researchers from NASA/JPL (Jet Propulsion Laboratory) in Pasadena, California, and the UCI (University of California), Irvine, have reported the first detection of sea level "fingerprints" in ocean observations: detectable patterns of sea level variability around the world resulting from changes in water storage on Earth's continents and in the mass of ice sheets. The results will give scientists confidence they can use these data to determine how much the sea level will rise at any point on the global ocean as a result of glacier ice melt. 17) 18)
Figure 5: Sea level rise fingerprints calculated from observations of mass changes in Greenland, Antarctica, continental glaciers and ice caps, and land water storage made by the GRACE satellites, January 2003 to April 2014 (image credit: NASA, UCI)
As ice sheets and glaciers undergo climate-related melting, they alter Earth's gravity field, resulting in sea level changes that aren't uniform around the globe. For example, when a glacier loses ice mass, its gravitational attraction is reduced. Ocean waters nearby move away, causing sea level to rise faster far away from the glacier. The resulting pattern of sea level change is known as a sea level fingerprint. Certain regions, particularly in Earth's middle and low latitudes, are hit harder, and Greenland and Antarctica contribute differently to the process. For instance, sea level rise in California and Florida generated by the melting of the Antarctic ice sheet is up to 52 percent greater than its average effect on the rest of the world.
To calculate sea level fingerprints associated with the loss of ice from glaciers and ice sheets and from changes in land water storage, the team used gravity data collected by the twin satellites of the U.S./German GRACE (Gravity Recovery and Climate Experiment) between April 2002 and October 2014. During that time, the loss of mass from land ice and from changes in land water storage increased global average sea level by about 1.8 mm per year, with 43 percent of the increased water mass coming from Greenland, 16 percent from Antarctica and 30 percent from mountain glaciers. The scientists then verified their calculations of sea level fingerprints using readings of ocean-bottom pressure from stations in the tropics.
Figure 6: Sea level fingerprints (patterns of variation in sea level rise) calculated from GRACE satellite observations, 2002-2014. The blue contour (1.8 mm per year) shows the average sea level rise if all the water added to the ocean were spread uniformly around Earth (image credit: NASA, UCI)
"Scientists have a solid understanding of the physics of sea level fingerprints, but we've never had a direct detection of the phenomenon until now," said co-author Isabella Velicogna, UCI professor of Earth system science and JPL research scientist. "It was very exciting to observe the sea level fingerprints in the tropics, far from the glaciers and ice sheets," said lead author Chia-Wei Hsu, a graduate student researcher at UCI.
GRACE is a joint NASA mission with the German Aerospace Center (DLR) and the German Research Center for Geosciences (GFZ), in partnership with the University of Texas at Austin.
Global Record Temperature Streak Study
August 10, 2017: The year 2016, aided in part by a historically large El Niño event, set a new global temperature record. We have thus witnessed three consecutive record breaking annual mean temperatures (2014, 2015, and 2016) in most global and/or hemispheric surface temperature series for the first time since historical observations began in the nineteenth century. It is reasonable to suspect that such an event would be extremely unlikely in the absence of anthropogenic warming, but it is worthwhile to ask just how unlikely such events actually are both with and without anthropogenic influence on climate. 19) 20)
Temperature records were first broken in 2014, when that year became the hottest year since global temperature records began in 1880. These temperatures were then surpassed in 2015 and 2016, making last year the hottest year ever recorded. In 2016, the average global temperature across land and ocean surface areas was 0.94 degrees Celsius above the 20th century average of 13.9 degrees Celsius,according to NOAA.
Winds Trigger Pond Growth
July 6, 2017: Wind is a force to be reckoned with. It can stir up monsoons, carry dust thousands of miles, and sculpt rock into sinuous arches. But sometimes, the effects of wind go unnoticed for years, like when it carves away slowly at the edges of a pond. 21)
A new study shows that winds are responsible for the widespread growth of ponds in three watersheds along the Mississippi River. The paper, published in April 2017 in Geophysical Research Letters, shows that wind-driven waves can erode pond banks, leading them to migrate in the direction of the wind. In effect, researchers have shown that wind-driven erosion, which nibbles away coastlines and the edges of larger bodies of water, can also happen inland on small scales. 22)
The researchers analyzed roughly 10,000 satellite images taken between 1982 and 2016, examining land and water pixels to look for inland change across the Mississippi River Delta. "Up until now, a lot of focus has been on coastal retreat," said Alejandra Ortiz, a marine geologist at Indiana University, Bloomington. Instead, Ortiz and colleagues focused on internal fragmentation; that is, what happens when land becomes subdivided by inland erosion processes. "Our thinking was, can you see this on large scale?"
Ortiz and her co-authors found that ponds in the Mississippi Delta tended to expand in a southwesterly direction, which is the same direction as the prevailing winds (which blow out of the northeast). This was especially true in Terrebonne and Barataria basins, where 80 percent of the ponds are expanding. The other study basin, the Atchafalaya-Vermillion, was deemed stable, with nearly as many ponds contracting as expanding—roughly 30 percent.
The false-color image of Figure 7 shows the area of study along the Atchafalaya Delta. It was captured on December 1, 2016, by OLI (Operational Land Imager) on Landsat 8. The colors emphasize the difference between land and water while allowing viewers to observe waterborne sediment, which is typically absent from false-color imagery.
Figure 7: OLI image on Landsat-8 of ponds in three watersheds along the Mississippi River south of New Orleans, acquired on December 1, 2016 (image credit: NASA Earth Observatory, images by Joshua Stevens, using Landsat data from the USGS and data from Ortiz, A. C., Roy, S., & Edmonds, D. A. (2017), story by Pola Lem)
The images of Figures 8 and 9 illustrate ponds that have grown (blue) or receded (orange) near the delta. In areas like Houma, Louisiana, the size of ponds increased significantly. The Terrebone and Barataria basins have much higher pond density, making them more susceptible to pond merging—when two or more ponds migrate toward each other and produce one larger body of water.
Figure 8: Landsat images (Landsat-7, Landsat-4, Landsat-5 and Landsat-8) of ponds that have grown (blue) or receded (orange) near the delta, acquired in the period 1982 - 2016 (image credit: NASA Earth Observatory, images by Joshua Stevens, using Landsat data from the USGS and data from Ortiz, A. C., Roy, S., & Edmonds, D. A. (2017), story by Pola Lem)
Some ponds were too small to generate waves strong enough to erode the shoreline. The researchers found that critical pond width was about 300 meters. Ponds at least that wide offer enough open space—for wind to gather momentum, or "fetch" as sailors and meteorologists call it—to create waves big enough to nibble away the shore.
Ortiz said the findings could affect the management of erosion-prone water bodies. For instance, managers could create physical barriers to prevent ponds from growing. "One possibility is thinking about putting in something that stops wave generation," she said.
Figure 9: Landsat images (Landsat-7, Landsat-4, Landsat-5 and Landsat-8) of ponds that have grown (blue) or receded (orange) near the delta, acquired in the period 1982 - 2016 (image credit: NASA Earth Observatory, images by Joshua Stevens, using Landsat data from the USGS and data from Ortiz, A. C., Roy, S., & Edmonds, D. A. (2017), story by Pola Lem)
Increasing rate of GMSL (Global Mean Sea Level) rise during 1993-2014
June 2017: Ocean levels rose 50 percent faster in 2014 than in 1993, with meltwater from the Greenland ice sheet now supplying 25 percent of total sea level increase compared with just five percent 20 years earlier, researchers reported on June 26, 2017. The findings add to growing concern among scientists that the global watermark is climbing more rapidly than forecast only a few years ago, with potentially devastating consequences. 23)
- The findings add to growing concern among scientists that the global watermark is climbing more rapidly than forecast only a few years ago, with potentially devastating consequences. Hundreds of millions of people around the world live in low-lying deltas that are vulnerable, especially when rising seas are combined with land sinking due to depleted water tables, or a lack of ground-forming silt held back by dams.
- Major coastal cities are also threatened, while some small island states are already laying plans for the day their drowning nations will no longer be livable.
- "This result is important because the IPCC (Intergovernmental Panel on Climate Change), the UN science advisory body, makes a very conservative projection of total sea level rise by the end of the century," at 60 to 90 cm, said Peter Wadhams, a professor of ocean physics at the University of Oxford who did not take part in the research.
- That estimate, he added, assumes that the rate at which ocean levels rise will remain constant. "Yet there is convincing evidence — including accelerating losses of mass from Greenland and Antarctica — that the rate is actually increasing, and increasing exponentially."
- Greenland alone contains enough frozen water to lift oceans by about 7 m, though experts disagree on the global warming threshold for irreversible melting, and how long that would take once set in motion.
- "Most scientists now expect total rise to be well over 1 m by the end of the century," Wadhams said.
- The new study, published in Nature Climate Change, reconciles for the first time two distinct measurements of sea level rise. 24)
- GMSL has been rising at a faster rate during the satellite altimetry period (1993–2014) than previous decades, and is expected to accelerate further over the coming century. However, the accelerations observed over century and longer periods2 have not been clearly detected in altimeter data spanning the past two decades. Here we show that the rise, from the sum of all observed contributions to GMSL, increases from 2.2 ± 0.3 mm yr-1 in 1993 to 3.3 ± 0.3 mm yr-1 in 2014. This is in approximate agreement with observed increase in GMSL rise, 2.4 ± 0.2 mm yr-1 (1993) to 2.9 ± 0.3 mm yr-1 (2014), from satellite observations that have been adjusted for small systematic drift, particularly affecting the first decade of satellite observations. 25)
- The mass contributions to GMSL increase from about 50% in 1993 to 70% in 2014 with the largest, and statistically significant, increase coming from the contribution from the Greenland ice sheet, which is less than 5% of the GMSL rate during 1993 but more than 25% during 2014. The suggested acceleration and improved closure of the sea-level budget highlights the importance and urgency of mitigating climate change and formulating coastal adaption plans to mitigate the impacts of ongoing sea-level rise.
Lightning Sparking More Boreal Forest Fires
June 26, 2017: A new NASA-funded study finds that lightning storms were the main driver of recent massive fire years in Alaska and northern Canada, and that these storms are likely to move farther north with climate warming, potentially altering northern landscapes. 26)
The study, led by Vrije Universiteit Amsterdam and the University of California, Irvine, examined the cause of the fires, which have been increasing in number in recent years. There was a record number of lightning-ignited fires in the Canadian Northwest Territories in 2014 and in Alaska in 2015. The team found increases of between two and five percent a year in the number of lightning-ignited fires since 1975. 27)
To study the fires, the team analyzed data from NASA's Terra and Aqua satellites and from ground-based lightning networks.
Lead author Sander Veraverbeke of Vrije Universiteit Amsterdam, who conducted the work while at UC Irvine, said that while the drivers of large fire years in the high north are still poorly understood, the observed trends are consistent with climate change. "We found that it is not just a matter of more burning with higher temperatures. The reality is more complex: higher temperatures also spur more thunderstorms. Lightning from these thunderstorms is what has been igniting many more fires in these recent extreme events," Veraverbeke said.
Study co-author Brendan Rogers at Woods Hole Research Center in Falmouth, Massachusetts, said these trends are likely to continue. "We expect an increasing number of thunderstorms, and hence fires, across the high latitudes in the coming decades as a result of climate change." This is confirmed in the study by different climate model outputs.
Study co-author Charles Miller of NASA's Jet Propulsion Laboratory in Pasadena, California, said while data from the lightning networks were critical to this study, it is challenging to use these data for trend detection because of continuing network upgrades. "A spaceborne sensor that provides high northern latitude lightning data that can be linked with fire dynamics would be a major step forward," he said.
The researchers found that the fires are creeping farther north, near the transition from boreal forests to Arctic tundra. "In these high-latitude ecosystems, permafrost soils store large amounts of carbon that become vulnerable after fires pass through," said co-author James Randerson of the University of California, Irvine. "Exposed mineral soils after tundra fires also provide favorable seedbeds for trees migrating north under a warmer climate."
"Taken together, we discovered a complex feedback loop between climate, lightning, fires, carbon and forests that may quickly alter northern landscapes," Veraverbeke concluded. "A better understanding of these relationships is critical to better predict future influences from climate on fires, and from fires on climate."
Figure 10: A lightning-caused wildfire burns in Alberta, Canada (image credit: The Government of Alberta)
Sea level as a metronome of Earth's history
May 19, 2017: Sedimentary layers contain stratigraphic cycles and patterns that precisely reveal the succession of climatic and tectonic conditions that have occurred over millennia. Researchers have been working on an analytical method that combines observing deep-water sedimentary strata and measuring in them the isotopic ratio between heavy and light carbon. They have discovered that the cycles that punctuate these sedimentary successions are ascribable to sea level changes. 28) 29) 30)
Sedimentary layers record the history of the Earth. They contain stratigraphic cycles and patterns that precisely reveal the succession of climatic and tectonic conditions that have occurred over millennia, thereby enhancing our ability to understand and predict the evolution of our planet.
Researchers at the University of Geneva (UNIGE), Switzerland, - together with colleagues at the University of Lausanne (UNIL) and American and Spanish scientists - have been working on an analytical method that combines observing deep-water sedimentary strata and measuring in them the isotopic ratio between heavy and light carbon.
They have discovered that the cycles that punctuate these sedimentary successions are not, as one might think, due solely to the erosion of mountains that surround the basin, but are more ascribable to sea level changes. This research, which you can read in the journal Geology, paves the way for new uses of isotopic methods in exploration geology.
The area south of the Pyrenees is particularly suitable for studying sedimentary layers. Rocks are exposed over large distances, allowing researchers to undertake direct observation. Turbidites can be seen here: large sediment deposits formed in the past by underwater avalanches consisting of sand and gravel.
The ups and downs of oceans regulate sedimentation cycles:
The variations in the ratio helped us explore the possible link with the sea level". The research team found that the turbidite-rich intervals were associated with high 12C levels, and almost always corresponded to periods when the sea level was low. It seems that sedimentary cycles are mainly caused by the rise and fall of the sea level and not by the episodic growth of mountains.
When the sea level is high, continental margins are flooded under a layer of shallow water. Since the rivers are no longer able to flow, they begin to deposit the sediments they carry there. This is why so little material reaches the deep basins downstream. When the sea level is low, however, rivers erode their beds to lower the elevation of their mouth; they transfer their sediment directly to the continental slopes of the deep basins, creating an avalanche of sand and gravel.
Consequently, if the variations of the sea level are known, it is possible to predict the presence of large sedimentary accumulations created by turbidites, which often contain large volumes of hydrocarbons, one of the holy grails of exploration geology.
Measuring stable carbon isotopes: a new indicator of reservoir rocks:
In addition, this measurement is relatively simple to perform and it provides accurate data - a real asset for science and mining companies. The study also highlights the importance of sea levels, which are a real metronome for the Earth's sedimentary history.
"Of course," concludes Honegger, "tectonic deformation and erosion are important factors in the formation of sedimentary layers; but they play a secondary role in the formation of turbidite accumulations, which are mainly linked to changes in the sea level".
Study of Ice-shelf Channel Formation in Antarctica
May 15, 2017: A team of scientists led by the ULB (Universite Libre de Bruxelles) Belgium and the Bavarian Academy of Sciences (Munich,Germany) have discovered an active hydrological system of water conduits and sediment ridges below the Antarctic ice sheet. Their study reveals that the scale of these subglacial features is five times bigger than those seen in today's deglaciated landscapes. 31)
The newly discovered, oversized sediment ridges actively shape the ice hundreds kilometers downstream, by carving deep incisions at the bottom of the ice. This is of interest for the stability of the floating ice shelves, as numerous studies show that ice shelf thinning has major consequences for ice sheet stability.
Subglacial conduits form under large ice sheets as part of their basal hydrological system. These tunnels have a typical diameter of several meters to tens of meters, and they funnel the subglacial melt water towards the ocean. However, new geophysical observations by the Laboratoire de Glaciologie of the ULB show that these conduits widen considerably the closer they come to the ocean. A new mathematical model explains this widening with the vanishing overburden pressure at the location where the ice becomes afloat on the ocean.
As the conduits widen, the outflow velocity of the subglacial water decreases, which leads to increased sediment deposition at the conduit's portal. Over thousands of years, this process builds up giant sediment ridges - comparable in height with the Eiffel tower - below the ice. Active sedimentation in subglacial water conduits seems to drive the formations of Eskers - elongated ridges of gravel which are commonly observed today in areas where former ice sheets have retreated. However, the remainders of today's Eskers are considerably smaller in size than those now discovered in Antarctica.
Ice-shelf channels are long curvilinear tracts of thin ice found on Antarctic ice shelves. Many of them originate near the grounding line, but their formation mechanisms remain poorly understood. The study team uses ice-penetrating radar data from the Roi Baudouin Ice Shelf, East Antarctica, to infer that the morphology of several ice-shelf channels is seeded upstream of the grounding line by large basal obstacles indenting the ice from below. The team interprets each obstacle as an esker ridge formed from sediments deposited by subglacial water conduits, and calculates that the eskers' size grows towards the grounding line where deposition rates are maximum. Relict features on the shelf indicate that these linked systems of subglacial conduits and ice-shelf channels have been changing over the past few centuries. Because ice-shelf channels are loci where intense melting occurs to thin an ice shelf, these findings expose a novel link between subglacial drainage, sedimentation and ice-shelf stability. 32)
Water beneath the Antarctic Ice Sheet promotes the formation of ice streams that rapidly slide over wet sediments and a lubricated base. Ice streams discharge the majority of Antarctic ice into floating ice shelves, which surround about 74% of the Antarctic perimeter. Ice shelves occupying embayments buttress the continental mass flux. The buttressing strength depends on the pattern of basal mass balance (i.e., the sum of melting and refreezing), which in turn influences ice-shelf geometry. Measurements show that basal melting is concentrated by ice-shelf channels, which are typically a few kilometers wide and extend for up to hundreds of kilometers along the shelf flow. Ice is thinnest along their central axes (sometimes thinner than half of the ice thickness), and basal melt rates are elevated at their onsets near the grounding line. Theory and satelliteborne observations suggest that such ‘subglacially sourced' ice-shelf channels are formed by buoyant melt-water plumes forced by basal melt water exiting from subglacial conduits at the grounding line. Hitherto, no such conduits have been observed, presumably because they are too small to be detected with ice-penetrating radar.
The study team surveyed three hydrologically predicted subglacial water-outlet locations at the Roi Baudouin Ice Shelf in Dronning Maud Land, Antarctica, all with corresponding ice-shelf channels seawards (Sites A–C, Figure 11a,b). Airborne radar data collected upstream of the satellite-inferred grounding line show distinct radar reflectors situated several hundred meters above the adjacent ice-bed interface (reflectors A–C, Figure 12 c). Using additional ground-based radar data from 2016, the team examined the reflectors' geometry in order to deduce their identity and evaluate three different scenarios for ice-shelf channel formation.
Figure 11: Overview of the study area: (a) Location of airborne (2011) and ground-based (2016) radar profiles of the Roi Baudouin Ice Shelf, East Antarctica, with Landsat image in the background. Grounding lines are marked for 1996, 2007 and 2016. The dashed white box delineates the area in b where radar-profile locations are shown with TanDEM-X surface elevation (5m contours), image credit: Study Team)
Figure 12: Overview of the study area: (c) Airborne radar profile EuA-EuA' covering the grounded ice sheet. Internal reflection hyperbolas reaching hundreds of meters above the ice-bed interface are evident (reflectors A–C), and are aligned with ice-shelf channels located seawards (into page). Reflectors A and C are beneath surface ridges (image credit: Study Team)
Giant conduits that can sap the ice from below: The evolving sediment ridges leave scars at the bottom of the ice as the ice flows over them. These scars are transmitted to the floating ice shelves farther downstream forming ice-shelf channels. Ice in these channels is up to half as thin as their surroundings, making them a weak spot when exposed to melting from the warmer ocean.
It was originally thought that ice-shelf channels are carved by melting due to the ocean only, but this seems only part of the story: "Our study shows that ice-shelf channels can already be initiated on land, and that the size of the channels significantly depends on sedimentation processes occurring over hundreds to thousands of years" indicates Reinhard Drews, lead author of the study.
The novel link between the subglacial hydrological system, sedimentation, and ice-shelf stability, offers new opportunities to unravel key processes beneath the Antarctic ice sheet, and also improves our ability to reconstruct the ice-sheet extent in the Northern Hemisphere during the last ice ages.
More information on this topic is provided in Ref. 32).
Glacial lakes grow in the Himalayas as well as the risks
• May 9, 2017: For people living around the Himalayas, the effects of global warming are anything but distant or abstract. As air temperatures have risen in the past half-century, glaciers have melted and retreated in these mountains. Between 1990 and 2015, Landsat satellites have documented a significant increase in both the number and average size of glacial lakes throughout the range. 33) 34) 35)
- Expanding lakes mean greater risks for the people living in valleys downstream. Specifically, there is a greater risk of GOLFs (Glacial Lake Outburst Floods)—a type of flash flood that occurs when ice or sediment dams collapse beneath glacial lakes. Landslides, avalanches, earthquakes, and volcanic eruptions often trigger GLOFs.
- After analyzing hundreds of satellite images, a research team from the Chinese Academy of Sciences and UCLA (University of California, Los Angeles) concluded that the number of Himalayan glacial lakes increased from 4,459 in 1990 to 4,950 in 2015, with a total area gain of 56 km2, or 14 percent.
- The degree of change varied by region. The size and number of lakes in the southern central Himalayas increased the most, particularly in Nepal, at elevations between 4,200 and 5,800 meters. In the map of Figure 13, regions where lakes expanded the most (20 percent or more) are shown with dark blue; regions where lakes grew only slightly (10 percent or less) are light blue. Lakes in the western Himalayas are generally more stable. Some glaciers in the Karakorum, for instance, are advancing. In contrast, rapid warming in the central Himalayas—as well as more soot being deposited on ice—may explain the rapid retreat of glaciers there.
Figure 13: Himalayan region effected by an increasing number of glacial lakes (image credit: NASA Earth Observatory, images by Jesse Allen, using Landsat data from the USGS, caption by Adam Voiland)
- The researchers observed changes to lakes at both the terminus of glaciers (proglacial lakes) and on top of them (supraglacial lakes). Between 1990 and 2015, the number of proglacial lakes increased by 227; the number of supraglacial lakes rose by 144. About 81 percent of the expansion in lake area was caused by changes to proglacial lakes.
- The researchers also identified 118 proglacial lakes that pose a particularly high risk to people living downstream. These lakes—many of them in the central Himalayas near Kathmandu, Nepal, and in the eastern Himalayas near Thimphu, Bhutan—grew by more than 1 percent each year.
- One rapidly expanding proglacial lake, Cirenmaco, highlights the risks. It stands at the base of Amaciren Glacier in the Zhangzangbo Valley of Nepal, and it was the scene of outburst floods in 1964 and 1981. The flood in 1981 was particularly destructive, killing hundreds of people, knocking out a power plant, and destroying bridges and roads. As seen in the false-color Landsat images (Figure 14), Cirenmaco's size more than doubled between 1988 and 2015.
- While proglacial lakes generally grew steadily each year, the lakes emerging on top of the glaciers were small, short-lived, and fast-changing. Many supraglacial lakes are perched on debris-covered ice, meaning lake water can quickly drain deeper into the glacier when cracks emerge.
Figure 14: Left: Image of Lake Cirenmaco acquired with Landsat-5 on Oct. 12, 1988; Right: Image of the same region acquired with Landsat-8 on Oct. 7, 2015 (image credit: NASA Earth Observatory, images by Jesse Allen, using Landsat data from the USGS, caption by Adam Voiland)
- Nepal's Ngozumpa Glacier (Figure 15), which lies about 25 km west of Mount Everest, has seen a significant increase in the number and size of supraglacial lakes on its surface. The pair of Landsat images below show the surface of the glacier in 1989 and 2015. Many of the lakes that existed in 1990 had drained by 2015, while many new lakes emerged in other areas.
- Researchers point to rising temperatures and melting glaciers as the primary cause for the increase in the size and number of lakes in the Himalayas. Rates of warming vary by region, but match the increases in total lake area. For instance, the team noted that between 1979 and 2014, temperatures rose by 5.9ºC at Nyalam in the central Himalaya; 1.0 ºC at Shiquanhe in the western Himalaya; and 0.4ºC at Yadong in the eastern Himalaya.
- "As the region continues to warm, it is urgent that scientists continue to monitor the most rapidly expanding glacial lakes with satellites because many are remote and very difficult to access," said Yong Nie, lead author of the study. "If we know which lakes pose the greatest risk, then authorities can take steps to develop early warning systems, drain specific high-risk lakes, and educate people on how to minimize their exposure to flash floods."
- Yongwei Sheng, a geography professor at UCLA and one of the study authors, added: "While we have reported on widespread lake expansion across the Himalayas, region-specific driving mechanisms, lake-specific risk assessments, as well as future change prediction all deserve further investigation."
Figure 15: Left: Landsat image of the Ngozumpa Glacier, acquired on Nov. 9, 1089; Right: Landsat-8 image of the same region acquired on Sept. 30, 2015 (image credit: NASA Earth Observatory, images by Jesse Allen, using Landsat data from the USGS, caption by Adam Voiland)
Regional Sea Level Scenarios for Coastal Risk Management
• May 2017: Sea level rise is occurring worldwide, but not at the same rate everywhere. Differences will also likely continue in the future, so decision-makers need local information to assess their community's vulnerability. These new scenarios integrate updated global sea level rise scenarios with regional factors, such as changes in land elevations and ocean circulation, that influence sea level regionally.
"The ocean is not rising like water would in a bathtub," said William Sweet, a NOAA oceanographer and lead author of the report detailing the scenarios. "For example, in some scenarios sea levels in the Pacific Northwest are expected to rise slower than the global average, but in the Northeast they are expected to rise faster. These scenarios will help communities better understand local trends and make decisions about adaptation that are best for them." 36) 37)
In the USA, the "Sea Level Rise and Coastal Flood Hazard Scenarios and Tools Interagency Task Force", jointly convened by the USGCRP (U.S. Global Change Research Program) and the NOC (National Ocean Council), began its work in August 2015. The Task Force has focused its efforts on three primary tasks: 1) updating scenarios of GMSL (Global Mean Sea Level) rise, 2) integrating the global scenarios with regional factors contributing to sea level change for the entire U.S. coastline, and 3) incorporating these regionally appropriate scenarios within coastal risk management tools and capabilities deployed by individual agencies in support of the needs of specific stakeholder groups and user communities.
Long-term sea level rise driven by global climate change presents clear and highly consequential risks to the United States over the coming decades and centuries. Today, millions of people in the United States already live in areas at risk of coastal flooding, with more moving to the coasts every year . Rising seas will dramatically increase the vulnerability of this growing population, along with critical infrastructure related to transportation, energy, trade, military readiness, and coastal ecosystems and the supporting services they provide.
GMSL (Global Mean Sea Level) has increased by about 21 cm to 24 cm since 1880, with about 8 cm occurring since 1993. In addition, the rate of GMSL rise since 1900 has been faster than during any comparable period over at least the last 2800 years. Scientists expect that GMSL will continue to rise throughout the 21st century and beyond, because of global warming that has already occurred and warming that is yet to occur due to the still-uncertain level of future emissions. GMSL rise is a certain impact of climate change; the questions are when, and how much, rather than if. There is also a long-term commitment (persistent trend); even if society sharply reduces emissions in the coming decades, sea level will most likely continue to rise for centuries.
While the long-term, upward shift in sea level is an underlying driver of changes to the nation's coasts, impacts are generally expressed through extreme water levels (short-period, lower-probability events both chronic and acute in nature) occurring against the background of this shifting baseline. Higher sea levels worsen the impacts of storm surge, high tides, and wave action, even absent any changes in storm frequency and intensity. Even the relatively small increases in sea level over the last several decades have led to greater storm impacts at many places along the U.S. coast. Similarly, the frequency of intermittent flooding associated with unusually high tides has increased rapidly (accelerating in many locations) in response to increases in RSL (Relative Sea Level ) as shown in Figure 16. At some locations in the United States, the frequency of tidal flooding (events typically without a local storm present) has increased by an order of magnitude over the past several decades, turning it from a rare event into a recurrent and disruptive problem. Significant, direct impacts of long-term RSL rise, including loss of life, damage to infrastructure and the built environment, permanent loss of land, ecological regime shifts in coastal wetlands and estuary systems, and water quality impairment, also occur when key thresholds in the coastal environment are crossed. Some of these impacts have the potential to ‘feedback' and influence wave impacts and coastal flooding. For example, there is evidence that wave action and flooding of beaches and marshes can induce changes in coastal geomorphology, such as sediment build up, that may iteratively modify the future flood risk profile of communities and ecosystems.
Figure 16: a) Multi-year empirical (smoothed) distributions for daily highest water levels in Norfolk, VA for the 1960s and 2010s, showing extent that local RSL rise has increased the flood probability relative to impact thresholds defined locally by the National Weather Service for minor (~0.5 m nuisance level), moderate (~0.9 m) and major (~1.2 m local level of Hurricane Sandy in 2012) impacts, relative to MHHW (Mean Higher High Water) tidal datum of the National Tidal Datum Epoch (1983–2001). b) Due to RSL rise, annual flood frequencies (based upon 5-year averages) in Norfolk for recurrent nuisance tidal floods with minor impacts are accelerating, as shown by the quadratic trend fit (goodness of fit [R2]=0.84). Flood rates are rapidly increasing in similar fashions along dozens of coastal cities of the U.S. (image credit: NOAA, USGS, EPA)
In this context, there is a clear need—and a clear call from states and coastal communities (White House, 2014)—to support preparedness planning with consistent, accessible, authoritative and more locally appropriate knowledge, data, information, and tools about future changes in sea level and associated coastal risks. In response to this need, the White House Council on Climate Preparedness and Resilience in 2015 called for the establishment of the Federal Interagency Sea Level Rise and Coastal Flood Hazard Scenarios and Tools Task Force, a joint task force of the NOC (National Ocean Council) and the USGCRP (U.S. Global Change Research Program ). The Task Force's charge is to develop and disseminate, through interagency coordination and collaboration, future RSL and associated coastal flood hazard scenarios and tools for the entire United States. These scenarios and tools are intended to serve as a starting point for on-the-ground coastal preparedness planning and risk management processes, including compliance with the new FFRMS (Federal Flood Risk Management Standard).
The Task Force is charged with leveraging the best available science; incorporating regional science and expertise where appropriate; building this information into user-friendly mapping, visualization, and analysis tools; and making it easily accessible through established Federal web portals. Part of the motivation for forming the Task Force was to bring together key efforts within individual agencies, such as the FEMA (Federal Emergency Management Agency), NOAA (National Oceanic and Atmospheric Administration), USACE (U.S. Army Corps of Engineers), USGS (U.S. Geological Survey), DoD (Department of Defense), EPA (Environmental Protection Agency) and NASA (National Aeronautics and Space Administration), that could serve as building blocks of an overall Federal system of sea level information and decision support, and to provide synthesis and coverage of the entire United States coastline.
• May 4, 2017: Thanks in large part to satellite measurements, scientists' skill in measuring how much sea levels are rising on a global scale - currently 3.4 mm per year - has improved dramatically over the past quarter century. But at the local level, it's been harder to estimate specific regional sea level changes 10 or 20 years away - the critical timeframe for regional planners and decision makers. 38)
That's because sea level changes for many reasons, on differing timescales, and is not the same from one place to the next. Developing more accurate regional forecasts of sea level rise will therefore have far-reaching benefits for the more than 30 percent of Americans who currently reside along the Pacific, Atlantic or Gulf Coasts of the contiguous United States.
New research published this week in the Journal of Climate reveals that one key measurement — large-scale upper-ocean temperature changes caused by natural cycles of the ocean — is a good indicator of regional coastal sea level changes on these decadal timescales. Such data may give planners and decision makers a new tool to identify key regions of U.S. coastlines that may be vulnerable to sea level changes on 10- to 20-year timescales. 39)
"Decision makers need a diverse set of tools with different informational needs," said lead author Veronica Nieves of UCLA and NASA's Jet Propulsion Laboratory in Pasadena, California. "Having a better understanding of the chances of local flood damage from rising seas in coastal areas is a key factor in being able to assess vulnerability, risk and adaptation options." Such tools could help planners decide whether a given part of a coastline would be better served by "soft" techniques, such as beach replenishment or preservation of wetlands, or by "hard" techniques, such as construction of sea walls or levees.
Nieves' team, which included participation from the IMEDEA (Mediterranean Institute for Advanced Studies) in Esporles, Spain, set out to detect decadal sea level changes over large U.S. coastal ocean regions. They compared existing NOAA records of upper-ocean temperatures in coastal waters for each U.S. ocean coastline with records of actual sea level changes from 1955 to 2012, and data from U.S./European satellite altimeter missions since 1992. They identified those sea level changes that have a large impact at regional scales in many locations, including largely populated cities. Sea level along the U.S. East Coast and West Coast can rise and fall by an inch or two (several centimeters) over the course of a decade or two because of fluctuations in upper ocean temperatures.
Their method was able to explain about 70 percent of regional sea level variability on decadal time scales for the West Coast, about 80 percent for the East Coast, and about 45 percent for the Gulf Coast. Along the Gulf Coast, the authors say other factors, such as tidal effects and the ongoing subsidence, or sinking, of the land, can play a more important role.
"Our study shows that large-scale upper-ocean temperature changes provide a good way to distinguish decade-long natural ocean signals from longer-term global warming signals," said Nieves. "This is important for regional planning, because it allows policymakers to identify places where climate change dominates the observed sea level rise and places where the climate change signal is masked by shorter-term regional variability caused by natural ocean climate cycles."
Nieves said an example is the U.S. West Coast, where the phase of a multi-decadal ocean climate pattern, called the Pacific Decadal Oscillation, has helped keep sea level rise lower during the past two decades. With the recent shift of this oscillation to its opposite phase, scientists expect sea level rise along the West Coast to accelerate in coming years.
"Scientists have worked hard to understand the really fast changes in sea level, such as storm surges, because they cause major damage, and the really slow changes because long-term sea level rise will shape the coastlines of the future," said study co-author Josh Willis of JPL. "But in between these fast and slow changes, there's a gap in our understanding. The results of our study help fill that gap."
Figure 17: Correlations in U.S. coastal sea level rise between the new sea level indicator tool and reconstructed decade-scale estimates of sea level (image credit: NASA/JPL-Caltech/UCLA/IMEDEA)
Sea Ice Extent Sinks to Record Lows at Both Poles
• March 22, 2017: Arctic sea ice appears to have reached on March 7 a record low wintertime maximum extent, according to scientists at NASA and the NASA-supported NSIDC (National Snow and Ice Data Center ) in Boulder, Colorado. And on the opposite side of the planet, on March 3 sea ice around Antarctica hit its lowest extent ever recorded by satellites at the end of summer in the Southern Hemisphere, a surprising turn of events after decades of moderate sea ice expansion. 40) 41) 42)
Figure 18: On March 7, 2017, Arctic sea ice hit a record low wintertime maximum extent in 2017. At 14.4 million km2, it is the lowest maximum extent in the satellite record, and 1.18 million km2 below the 1981 to 2010 average maximum extent (image credit: NASA/GSFC Scientific Visualization Studio, L. Perkins)
On Feb. 13, 2017, the combined Arctic and Antarctic sea ice numbers were at their lowest point since satellites began to continuously measure sea ice in 1979. Total polar sea ice covered 16.21 million km2, which is 2 million km2 less than the average global minimum extent for 1981-2010 – the equivalent of having lost a chunk of sea ice larger than Mexico.
Figure 19: These line graphs plot monthly deviations and overall trends in polar sea ice from October 1978 to March 7, 2017 as measured by satellites. The top line shows the Arctic; the middle shows Antarctica; and the third shows the global, combined total. The graphs depict how much the sea ice concentration moved above or below the long-term average (they do not plot total sea ice concentration). Arctic and global sea ice totals have moved consistently downward over 38 years. Antarctic trends are more muddled, but they do not offset the great losses in the Arctic (image credit: Joshua Stevens, NASA Earth Observatory)
The ice floating on top of the Arctic Ocean and surrounding seas shrinks in a seasonal cycle from mid-March until mid-September. As the Arctic temperatures drop in the autumn and winter, the ice cover grows again until it reaches its yearly maximum extent, typically in March. The ring of sea ice around the Antarctic continent behaves in a similar manner, with the calendar flipped: it usually reaches its maximum in September and its minimum in February.
This winter, a combination of warmer-than-average temperatures, winds unfavorable to ice expansion, and a series of storms halted sea ice growth in the Arctic. This year's maximum extent, reached on March 7 at 14.42 million km2, is 96,000 km2 below the previous record low, which occurred in 2015, and 1.22 million km2 smaller than the average maximum extent for 1981-2010.
Figure 20: On March 3, 2017, the sea ice cover around the Antarctic continent shrunk to its lowest yearly minimum extent in the satellite record, in a dramatic shift after decades of moderate sea ice expansion (image credit: NASA/GSFC Scientific Visualization Studio, L. Perkins)
Figure 21: Alternate view view of Arctic sea ice extend, acquired on March 7, 2017 (image credit: NASA Earth Observatory, image by Joshua Stevens using AMSR-2 sensor data on GCOM-W1)
"We started from a low September minimum extent," said Walt Meier, a sea ice scientist at NASA/GSFC in Greenbelt, Maryland. "There was a lot of open ocean water and we saw periods of very slow ice growth in late October and into November, because the water had a lot of accumulated heat that had to be dissipated before ice could grow. The ice formation got a late start and everything lagged behind – it was hard for the sea ice cover to catch up."
The Arctic's sea ice maximum extent has dropped by an average of 2.8 % per decade since 1979. The summertime minimum extent losses are nearly five times larger: 13.5% per decade. Besides shrinking in extent, the sea ice cap is also thinning and becoming more vulnerable to the action of ocean waters, winds and warmer temperatures.
This year's record low sea ice maximum extent might not necessarily lead to a new record low summertime minimum extent, since weather has a great impact on the melt season's outcome, Meier said. "But it's guaranteed to be below normal."
In Antarctica, this year's record low annual sea ice minimum of 2.11 million km2 was 184,000 km2 below the previous lowest minimum extent in the satellite record, which occurred in 1997.
Antarctic sea ice saw an early maximum extent in 2016, followed by a very rapid loss of ice starting in early September. Since November, the daily Antarctic sea ice extent has continuously been at its lowest levels in the satellite record. The ice loss slowed down in February.
This year's record low happened just two years after several monthly record high sea ice extents in Antarctica and decades of moderate sea ice growth. "There's a lot of year-to-year variability in both Arctic and Antarctic sea ice, but overall, until last year, the trends in the Antarctic for every single month were toward more sea ice," said Claire Parkinson, a senior sea ice researcher at Goddard. "Last year was stunningly different, with prominent sea ice decreases in the Antarctic. To think that now the Antarctic sea ice extent is actually reaching a record minimum, that's definitely of interest."
"It is tempting to say that the record low we are seeing this year is global warming finally catching up with Antarctica," Meier said. "However, this might just be an extreme case of pushing the envelope of year-to-year variability. We'll need to have several more years of data to be able to say there has been a significant change in the trend."
NASA, NOAA data show 2016 warmest year on record globally
• January 18, 2017: Earth's 2016 surface temperatures were the warmest since modern record-keeping began in 1880, according to independent analyses by NASA and NOAA (National Oceanic and Atmospheric Administration). Globally-averaged temperatures in 2016 were 0.99 degrees Celsius warmer than the mid-20th century mean. This makes 2016 the third year in a row to set a new record for global average surface temperatures. 43)
The 2016 temperatures continue a long-term warming trend, according to analyses by scientists at NASA/GISS ( Goddard Institute for Space Studies) in New York. NOAA scientists concur with the finding that 2016 was the warmest year on record based on separate, independent analyses of the data.
Figure 22: Global temperature anomalies averaged from 2012 through 2016 in degrees Celsius (image credit: NASA/GSFC Scientific Visualization Studio; data provided by Robert B. Schmunk, NASA/GSFC GISS)
Because weather station locations and measurement practices change over time, there are uncertainties in the interpretation of specific year-to-year global mean temperature differences. However, even taking this into account, NASA estimates 2016 was the warmest year with greater than 95 percent certainty. "2016 is remarkably the third record year in a row in this series," said GISS Director Gavin Schmidt. "We don't expect record years every year, but the ongoing long-term warming trend is clear." The planet's average surface temperature has risen about 1.1 degrees Celsius since the late 19th century, a change driven largely by increased carbon dioxide and other human-made emissions into the atmosphere.
Most of the warming occurred in the past 35 years, with 16 of the 17 warmest years on record occurring since 2001. Not only was 2016 the warmest year on record, but eight of the 12 months that make up the year – from January through September, with the exception of June – were the warmest on record for those respective months. October, November, and December of 2016 were the second warmest of those months on record – in all three cases, behind records set in 2015.
Phenomena such as El Niño or La Niña, which warm or cool the upper tropical Pacific Ocean and cause corresponding variations in global wind and weather patterns, contribute to short-term variations in global average temperature. A warming El Niño event was in effect for most of 2015 and the first third of 2016. Researchers estimate the direct impact of the natural El Niño warming in the tropical Pacific increased the annual global temperature anomaly for 2016 by 0.12 degrees Celsius.
Weather dynamics often affect regional temperatures, so not every region on Earth experienced record average temperatures last year. For example, both NASA and NOAA found the 2016 annual mean temperature for the contiguous 48 United States was the second warmest on record. In contrast, the Arctic experienced its warmest year ever, consistent with record low sea ice found in that region for most of the year.
Figure 23: The planet's long-term warming trend is seen in this chart of every year's annual temperature cycle from 1880 to the present, compared to the average temperature from 1880 to 2015. Record warm years are listed in the column on the right (image credit: NASA/Earth Observatory, Joshua Stevens)
NASA's analyses incorporate surface temperature measurements from 6,300 weather stations, ship- and buoy-based observations of sea surface temperatures, and temperature measurements from Antarctic research stations. These raw measurements are analyzed using an algorithm that considers the varied spacing of temperature stations around the globe and urban heating effects that could skew the conclusions. The result of these calculations is an estimate of the global average temperature difference from a baseline period of 1951 to 1980.
NOAA scientists used much of the same raw temperature data, but with a different baseline period, and different methods to analyze Earth's polar regions and global temperatures.
GISS is a laboratory within the Earth Sciences Division of NASA's Goddard Space Flight Center in Greenbelt, Maryland. The laboratory is affiliated with Columbia University's Earth Institute and School of Engineering and Applied Science in New York.
Changing rainfall patterns linked to water security in India
• January 11, 2017: Changing rainfall is the key factor driving changes in groundwater storage in India, according to a new study led by the IIT (Indian Institute of Technology) Gandhinagar published in the journal Nature Geoscience. The study shows that changing monsoon patterns - which are tied to higher temperatures in the Indian Ocean - are an even greater driver of change in groundwater storage than the pumping of groundwater for agriculture. 44) 45)
Agriculture in India relies heavily on groundwater for irrigation, particularly in the dry northern regions where precipitation is scarce. Groundwater withdrawals in the country have increased over tenfold since the 1950's, from 10-20 km3 per year in 1950, to 240-260 km3 per year in 2009. And satellite measurements have shown major declines in groundwater storage in some parts of the country, particularly in northern India.
"Groundwater plays a vital role in food and water security in India. Sustainable use of groundwater resources for irrigation is the key for future food grain production," says study leader Vimal Mishra, of the IIT Gandhinagar. "And with a fast-growing population, managing groundwater sustainably is going become even more important. The linkage between monsoon rainfall and groundwater can suggest ways to enhance groundwater recharge in India and especially in the regions where rainfall has been declining, such as the Indo-Gangetic Plain."
Groundwater acts like a bank for water storage, receiving deposits from surface water and precipitation, and withdrawals as people pump out water for drinking, industry, and irrigating fields. If withdrawals add up to more than the deposits, eventually the accounts could run dry, which could have disastrous consequences.
"This study adds another dimension to the existing water management framework. We need to consider not just the withdrawals, but also the deposits in the system," says Yoshihide Wada, a study coauthor and the deputy director of the Water program at the IIASA (International Institute for Applied Systems Analysis) in Austria.
The issue of groundwater depletion has been a topic of much discussion in India, but most planning has focused on pumping, or the demand side, rather than the deposit side. By looking at water levels in wells around the country, the researchers could track groundwater replenishment following the monsoons. They found that in fact, variability in the monsoons is the key factor driving the changing groundwater storage levels across the country, even as withdrawals increase.
In addition, the researchers found that the monsoon precipitation is correlated with Indian Ocean temperature, a finding which could potentially help to improve precipitation forecasts and aid in water resource planning.
"Weather is uncertain by nature, and the impacts of climate change are extremely difficult to predict at a regional level," says Wada "But our research suggests that we must focus more attention on this side of the equation if we want to sustainably manage water resources for the future."
Figure 24: Changing precipitation in India in the period 1980-2013 (image credit: IIT)
Ozone Hole 2016, and a Historic Climate Agreement
• October 27, 2016: The size and depth of the ozone hole over Antarctica was not remarkable in 2016. As expected, ozone levels have stabilized, but full recovery is still decades away. What is remarkable is that the same international agreement that successfully put the ozone layer on the road to recovery is now being used to address climate change. 46)
The stratospheric ozone layer protects life on Earth by absorbing ultraviolet light, which damages DNA in plants and animals (including humans) and leads to health issues like skin cancer. Prior to 1979, scientists had never observed ozone concentrations below 220 Dobson Units. But in the early 1980s, through a combination of ground-based and satellite measurements, scientists began to realize that Earth's natural sunscreen was thinning dramatically over the South Pole. This large, thin spot in the ozone layer each southern spring came to be known as the ozone hole.
The image of Figure 25 shows the Antarctic ozone hole on October 1, 2016, as observed by the OMI (Ozone Monitoring Instrument) on NASA's Aura satellite. On that day, the ozone layer reached its average annual minimum concentration, which measured 114 Dobson Units. For comparison, the ozone layer in 2015 reached a minimum of 101 Dobson Units. During the 1960s, long before the Antarctic ozone hole occurred, average ozone concentrations above the South Pole ranged from 260 to 320 Dobson Units.
The area of the ozone hole in 2016 peaked on September 28, 2016, at about 23 million km2. "This year we saw an ozone hole that was just below average size," said Paul Newman, ozone expert and chief scientist for Earth Science at NASA's Goddard Space Flight Center. "What we're seeing is consistent with our expectation and our understanding of ozone depletion chemistry and stratospheric weather."
The image of Figure 26 was acquired on October 2 by the OMPS (Ozone Mapping Profiler Suite) instrumentation during a single orbit of the Suomi-NPP satellite. It reveals the density of ozone at various altitudes, with dark orange areas having more ozone and light orange areas having less. Notice that the word hole isn't literal; ozone is still present over Antarctica, but it is thinner and less dense in some areas.
Figure 25: Image of the Antarctic Ozone Hole acquired with OMI on Aura on October 1, 2016 (image credit: NASA Earth Observatory, Aura OMI science team)
Figure 26: An edge-on (limb) view of Earth's ozone layer, acquired with OMPS on the Suomi-NPP on October 2, 2016 (image credit: NASA Earth Observatory, image by Jesse Allen, using Suomi-NPP OMPS data)
In 2014, an assessment by 282 scientists from 36 countries found that the ozone layer is on track for recovery within the next few decades. Ozone-depleting chemicals such as chlorofluorocarbons (CFCs)—which were once used for refrigerants, aerosol spray cans, insulation foam, and fire suppression—were phased out years ago. The existing CFCs in the stratosphere will take many years to decay, but if nations continue to follow the guidelines of the Montreal Protocol, global ozone levels should recover to 1980 levels by 2050 and the ozone hole over Antarctica should recover by 2070.
The replacement of CFCs with hydrofluorocarbons (HFCs) during the past decade has saved the ozone layer but created a new problem for climate change. HFCs are potent greenhouse gases, and their use — particularly in refrigeration and air conditioning — has been quickly increasing around the world. The HFC problem was recently on the agenda at a United Nations meeting in Kigali, Rwanda. On October 15, 2016, a new amendment greatly expanded the Montreal Protocol by targeting HFCs, the so-called "grandchildren" of the Montreal Protocol.
"The Montreal Protocol is written so that we can control ozone-depleting substances and their replacements," said Paul Newman, who participated in the meeting in Kigali. "This agreement is a huge step forward because it is essentially the first real climate mitigation treaty that has bite to it. It has strict obligations for bringing down HFCs, and is forcing scientists and engineers to look for alternatives."
NASA Releases First Map of Thawed Areas under Greenland's Ice Sheet
• August 2016: NASA researchers have helped produce the first map showing what parts of the bottom of the massive Greenland Ice Sheet are thawed – key information in better predicting how the ice sheet will react to a warming climate. 47)
Greenland's thick ice sheet insulates the bedrock below from the cold temperatures at the surface, so the bottom of the ice is often tens of degrees warmer than at the top, because the ice bottom is slowly warmed by heat coming from the Earth's depths. Knowing whether Greenland's ice lies on wet, slippery ground or is anchored to dry, frozen bedrock is essential for predicting how this ice will flow in the future, But scientists have very few direct observations of the thermal conditions beneath the ice sheet, obtained through fewer than two dozen boreholes that have reached the bottom. Now, a new study synthesizes several methods to infer the Greenland Ice Sheet's basal thermal state –whether the bottom of the ice is melted or not– leading to the first map that identifies frozen and thawed areas across the whole ice sheet.
"We're ultimately interested in understanding how the ice sheet flows and how it will behave in the future," said Joe MacGregor, lead author of the study and a glaciologist at NASA's Goddard Space Flight Center in Greenbelt, Md. "If the ice at its bottom is at the melting point temperature, or thawed, then there could be enough liquid water there for the ice to flow faster and affect how quickly it responds to climate change."
For this study, published last month in the Journal of Geophysical Research – Earth Surface, MacGregor's team combined four different approaches to investigate the basal thermal state. First, they examined results from eight recent computer models of the ice sheet, which predict bottom temperatures. Second, they studied the layers that compose the ice sheet itself, which are detected by radars onboard NASA's Operation IceBridge aircraft and suggest where the bottom of the ice is melting rapidly. Third, they looked at where the ice surface speed measured by satellites exceeds its "speed limit", the maximum velocity at which the ice could flow and still be frozen to the rock beneath it. Fourth, they studied imagery from the MODIS (Moderate Resolution Imaging Spectroradiometers) on the NASA Terra and Aqua satellites looking for rugged surface terrain that is usually indicative of ice sliding over a thawed bed. 48)
"Each of these methods has strengths and weaknesses. Considering just one isn't enough. By combining them, we produced the first large-scale assessment of Greenland's basal thermal state," MacGregor said. For each method, MacGregor's team looked for areas where the technique confidently inferred that the bed of Greenland's ice sheet was thawed or frozen. They then looked at the places where these methods agreed and classified these areas as likely thawed or likely frozen. The zones where there was insufficient data or the methods disagreed, they classified as uncertain.
From this synthesis, MacGregor and his colleagues determined that the bed is likely thawed under Greenland's southwestern and northeastern ice drainages, while it's frozen in the interior and west of the ice sheet's central ice divide. For a third of the Greenland ice sheet, there's not enough data available to determine its basal thermal state.
MacGregor said the team's map (Figure 27) is just one step in fully assessing the thermal state of the bottom of Greenland's ice sheet. "I call this the piñata, because it's a first assessment that is bound to get beat up by other groups as techniques improve or new data are introduced. But that still makes our effort essential, because prior to our study, we had little to pick on."
Figure 27: This first-of-a-kind map, showing which parts of the bottom of the Greenland Ice Sheet are likely thawed (red), frozen (blue) or still uncertain (gray), will help scientists better predict how the ice will flow in a warming climate (image credit: NASA Earth Observatory, Jesse Allen)
Study of hazardous thunderstorm intensification over Lake Victoria
• Sept. 22, 2016: An international study has determined that Lake Victoria in East Africa will become a hotspot for hazardous thunderstorms due to climate change using techniques that could improve regional climate and weather forecasts around inland bodies of water in the United States. 49)
Lake Victoria is divided among Uganda, Kenya and Tanzania. With a surface area close to 70,000 km2, it is the biggest lake in Africa. The lake is also a notoriously dangerous place for the 200,000 people who go fishing there at night. The International Red Cross estimates that between 3,000 and 5,000 fishermen per year lose their lives in violent storms on the lake.
Climate scientist Wim Thiery, affiliated with KU Leuven (Catholic University of Leuven, Belgium) and ETH Zürich (Swiss Federal Institute of Technology in Zürich, Switzerland), was able provide scientific evidence for why the storms occur in collaboration with colleague Kristopher Bedka of NASA's Langley Research Center in Hampton, Virginia.
"Thanks to new satellite-based storm detection products developed at NASA, we were able to map the number of hazardous thunderstorms and their locations in East Africa – every 15 minutes for a period ranging from 2005 to 2013," Thiery said. "During the day, most storms rage over the surrounding land, especially the typical afternoon thunderstorms that are caused by local upsurges of warm air. At night, these storms concentrate above Lake Victoria."
The storms are caused by circulation in the atmosphere above Victoria's enormous surface, according to Thiery. Daytime breezes flow outward from the cool water toward the warm land. At night, the opposite happens. Land breezes converge over the lake. Add in evaporation and you end up with storms.
To predict the impact of climate change on this process, Thiery ran climate simulations using an advanced computer model and determined that if the emission of greenhouse gases continues to increase, the extreme amounts of rainfall over Lake Victoria will increase by twice as much as the rainfall over the surrounding land. As a result, the lake will become a hotspot for night-time storms. "We found out that it is crucial to run our climate model at high resolution, and to couple a lake model to our climate model," Thiery said. "Resolving the lakes and getting lake surface temperatures right in the model is crucial to predicting the impact of these lakes on the regional climate and to get better projections of climate change."
The same advanced computer modeling could be useful in predicting future impacts of climate change around inland bodies of water in the U.S. "When performing climate simulations, it is very important to allow the body of water to accurately modify the atmosphere around it and vice versa," said Bedka, a climate scientist at NASA Langley. "Lakes and wide rivers such as Lake Michigan, the Mississippi River and, locally, the James River generate air circulations that can impact where thunderstorms form over the surrounding land. If climate projections do not properly account for these detailed interactions between land and water, they will underestimate their impact."
Properly coupled high-resolution models would be especially useful if these bodies of water were to warm up by a few degrees. That warming would have an impact on regional climate, and without precise modeling that impact could be difficult to predict and mitigate.
In addition, the satellite-based storm detection products that were crucial to the Lake Victoria study could also be useful in the U.S. Bedka and his team at NASA developed methods to automatically identify hazardous thunderstorms in "any satellite image, anytime, anywhere across the world." Lengthy datasets drawn from those methods could be used in the U.S. to help uncover interactions between land and water with a great degree of clarity.
Satellite data analysis: Satellite observations enable the recognition of severe weather by detecting OTs (Overshooting Tops) , that is, dome-like protrusions atop a cumulonimbus anvil induced by intense updrafts. OTs mark the presence of vigorous thunderstorms and are tightly linked to severe weather reports. By applying an OT detection algorithm to Methods (Meteosat Second Generation observations), the team established a new severe thunderstorm climatology for East Africa. The results reveal a marked imprint of Lake Victoria on the diurnal thunderstorm cycle and confirm its status as one of the most convectively active regions on Earth (Figure 28). From 2005 to 2013, 73% of all 1,400,000 OT pixels detected over the lake occurred at night (22:00 to 9:00 UTC), in contrast to the surrounding land where afternoon storms dominate (72% of all 4,200,000 OT pixels during 9:00 to 16:00 UTC). Local evaporation and mesoscale circulation have been identified as key drivers of the present-day diurnal cycle of precipitation over Lake Victoria, but so far it is not known how mean and extreme precipitation over this lake respond to a temperature increase induced by anthropogenic greenhouse gas emissions. To address this question, the team performed a high resolution (~7 km grid spacing), coupled lake–land–atmosphere climate projection for the African Great Lakes region with the regional climate model COSMO/CLM2 (Consortium for Small-scale Modeling/Community Land Model2), and analyzed coarser-scale ensemble projections from CORDEX (Coordinated Regional climate Downscaling Experiment) for the end of the century under a high-emission scenario. 50)
Figure 28: Lake imprint on severe thunderstorm occurrence. (a,b) Satellite-based overshooting tops (OT) detections during 2005–2013 over the Lake Victoria region (red square in the inset panel), from 9:00 to 15:00 UTC and from 00:00 to 9:00 UTC, respectively, as derived from the SEVIRI (Spinning Enhanced Visible and Infrared Imager) of Methods (image credit: Thunderstorm Study Team)
Extreme precipitation projections: The projections show a contrasting change of mean and extreme precipitation over Lake Victoria (Figure 29), with mean precipitation decreasing while the intensity of extreme precipitation increases. Moreover, by the end of the century the increase in extremes (precipitation above the 99th percentile) is 2.4±0.1 times higher over the lake than over its surrounding land in the highresolution projection (1.8±1.0 times in the CORDEX ensemble). Today convection initiates in the eastern part of the lake and intensifies while being advected westwards along the trade winds. In the future, storms are projected to release extreme precipitation more in the eastern part of the lake, leading to an eastward shift of intense precipitation (Figure 29a,b).
Figure 29: Projected end-of-century changes in extreme precipitation over Lake Victoria. (a) Night-time 99th percentile precipitation (P99%,night, 00:00 to 9:00 UTC) and (b) its projected future change from the high-resolution COSMO/CLM2 model. (c,d) 24 h Lake (blue bars) and surrounding land (red bars) binned precipitation change (P bin) from COSMO/CLM2 and the ensemble mean of nine CORDEX-Africa members, respectively (image credit: Thunderstorm Study Team)
The results emphasize a major hazard associated with climate change over East Africa with potential severe human impacts. Lake Victoria directly sustains the livelihood of 30 million people living at its coasts and its fishing industry is a leading natural resource for East African communities. However, given the projected increase in extreme over-lake thunderstorms, the current vulnerability of local fishing communities and their growing exposure driven by rapid urbanization along the lakefront, this lake is likely to remain the most dangerous stretch of water in the world. At the same time, the findings mark an opportunity for developing a satellite-based early warning system for hazardous thunderstorms over Lake Victoria.
Climate change already accelerating sea level rise, study finds
• August 10, 2016: Greenhouse gases are already having an accelerating effect on sea level rise, but the impact has so far been masked by the cataclysmic 1991 eruption of Mount Pinatubo in the Philippines, according to a new study led by NCAR (National Center for Atmospheric Research), Boulder, CO. 51) 52)
Driven by both the warming of the oceans and mass loss of the cryosphere,GSML (Global Mean Sea Level) is among the most powerful indicators of a changing climate. Originally estimated from a network of tide gages and restricted to coastlines, it has been derived from satellite measurements over the ice-free oceans since shortly after the launch of the TOPEX/Poseidon satellite in late 1992 with unprecedented accuracy and stability. During a given year, the height of the global seas can now be estimated to within a few millimeters revealing a mean rise of just over 3 mm yr-1. However the holistic nature of sea level has also led to challenges in its interpretation and it can be unclear at times whether its variations arise from changes in ocean heating, cryospheric melting, or the amount of water stored over land. Disentangling these various influences remains an ongoing science objective.
Among the major unanswered questions is why GMSL acceleration has not yet been detected in the altimeter record, given the increasing rates at which glacial and ice sheet melt are estimated to have occurred and as greenhouse gas concentrations have risen. The answer to this question has considerable policy relevance and debates over whether such an expected acceleration should be considered at the local policy level have at times been contentious. GMSL also has the potential to serve as an early indicator of accelerated climate change as it is less sensitive to the large internal variability that characterizes the surface temperature record, as evidenced by the recent so-called hiatus in global warming. Prevailing hypotheses for the lack of observed acceleration have maintained that changes in water storage over land or even drift in the satellite instruments may be to blame. Here it is demonstrated that the environment in which the era began was itself highly anomalous due to the preceding eruption of Mt Pinatubo on June 15, 1991, which cooled the oceans and decreased water storage over land and in the atmosphere. The net effect of these changes was to lower sea level prior to the altimeter era and induce an anomalous rise in the era's early years. It is proposed that this early anomalous rise masked the acceleration that would have otherwise occurred in the broader record. A consequence of this interpretation is that as the altimeter record lengthens, and in the coming decade barring another major volcanic eruption, accelerated rise will likely be detected.
Since late 1992 until the present, the TOPEX/Poseidon (T/P), Jason-1, and Jason-2 satellite altimeter missions have continuously measured sea level changes between ± 66º latitude with a temporal resolution of about 10 days, as shown in Figure 30. With their precision orbit determination, dual-frequency measurements (to remove ionosphere delays) and microwave radiometer (to remove delays due to water vapor in the troposphere), these missions have created an unrivaled 23-year climate data record of sea level change that is now being extended with the successful launch and deployment of the Jason-3 satellite earlier this year. Great care has been taken in calibrating these measurements via overlaps between missions and comparison to tide gauge sea level data. When averaged globally, the record provides an estimate of GMSL with a seasonal mean accuracy of 1–2 mm2.
Over the 23-year time series, it shows that GMSL has been rising at a rate of 3.3 ± 0.4 mm yr-1, but with notable inter-decadal variability.The current best estimate of the rates during the first (1993–2002) and second (2003– 2012) decades of the altimeter era are 3.5 and 2.7 mm yr-1, respectively, though important sources of uncertainty persist and raise caution regarding the record's early years (dashed line, Figure 30). There are several theories to explain this variability, but here we present an additional explanation, with important implications for anticipated near-future acceleration.
Figure 30: The altimeter record with decadal rates of change indicated (image credit: NCAR study team)
Legend to Figure 30: Estimates during the early stages of the record (dashed) are particularly subject to instrument related uncertainty.
Insight from Tide Gages: Prior to satellite altimetry, the primary source of sea level data is from historical tide gage records. These data provide a significantly longer time series relative to that of satellite altimetry, with a few records extending back into the 18th century. Several studies have estimated GMSL from the tide gage record using a variety of techniques. The resulting estimates of the GMSL trend from 1900 to 1990 range from 1.2 mm yr-1 to 1.9 mm yr-1, albeit with significant decadal variability about this long-term trend. Coupled with the higher GMSL trend observed during the satellite altimeter record discussed above, the tide gage record demonstrates unequivocal acceleration since the early 1900 s, with estimates ranging from 0.009 ± 0.002 mm yr-2 to 0.017 ± 0.003 mm yr-2. Based on these same studies, however, the majority of the acceleration arises from a shift that occurs around 1990 when the rate of sea level rise increases to the satellite-measured trend of 3.3 mm yr-1.
While the tide gage record may provide a ballpark estimate for what to expect during the altimeter era, it provides only weak quantitative information regarding what acceleration should be expected. In practice, calculating GMSL from 1900 to the present is a challenging problem based on the spatial and temporal sampling characteristics of available gages. There is little consensus across tide gage studies on the rate and acceleration of GMSL over the past century, thus making it difficult to interpret the altimeter era in a broader context. As an alternative approach to understanding sea level variability, we therefore seek to estimate and remove effects that obscure a possible underlying acceleration from the altimeter record itself. By doing so, we can potentially estimate the acceleration in GMSL directly from altimetry.
The GMSL Influence of the 1991 Mt Pinatubo Eruption: On June 15, 1991 the second largest volcanic eruption of the twentieth century in terms of aerosol radiative forcing began on the Philippine island of Luzon. Estimates of the amount of ash deposited in the stratosphere ranged from 20 to 30 Tg21 (approximately equal to a tenth the mass of all mankind) inducing a cooling of the globe and especially the world's oceans. Model-based estimates of the eruption's cooling effects suggest that the recovery of ocean heat content during the 1990's may have increased sea level rise by as much as 0.5 mm yr-1 on average in the decade following the eruption. The precise temporal evolution of the increase, and the impacts of the eruption on terrestrial and atmospheric water reservoirs remain largely unknown however; as quantifying these impacts is complicated by contemporaneous climate variability that can mask or amplify the response. Moreover, as many of the tools now in place for monitoring climate, such as for example the ARGO network of ocean temperature sensors and the GRACE satellite for estimating terrestrial water storage, were yet to be deployed at the time of the eruption, quantifying its precise climatic effects is nontrivial. However, recent specially designed climate model experiments now provide additional insight. What they reveal is that the eruption had a profound and temporally complex influence on several contributors to sea level and especially the amount of heat stored in the oceans, even when compared to background variations in climate, with major consequences for perceptions of GMSL acceleration during the altimeter era.
The CESM (Community Earth System Model) LE (Large Ensemble) is a 40-member ensemble of state-of-the-art coupled climate simulations spanning the 20th and 21st centuries using estimated historical forcings including volcanic eruptions. The simulated responses of GMSL and its individual contributors to the 1991 eruption of Mt Pinatubo are summarized in Figure 31. Immediately following the eruption, aerosols in the stratosphere blocked sunlight and cooled the surface. Surface temperatures quickly dropped, particularly over land due to its relative lack of thermal inertia. In turn, the atmosphere cooled, reducing the amount of moisture stored within it as water vapor. A cooler surface evaporated less moisture and was less convectively unstable, leading to a subsequent reduction in rainfall globally and disproportionately over land where diminished land water storage and runoff were a consequence of the eruption.
As these terrestrial and atmospheric changes are associated with reductions in their storage of water, their initial influence was to delay by about six months the eruption's main effect on sea level, which was a significant and rapid drop arising from a reduction in ocean heat content (OHC). The short timescale of the terrestrial and atmospheric influences relative to the oceans however limited their persistence, and by the beginning of the altimeter era in 1993, a GMSL drop of 5 to 7 mm from the eruption is estimated to have occurred, due largely to cooling of the oceans. While the LE's estimated OHC deficit is difficult to verify directly, given the large uncertainties and errors inherent in global ocean observations, confidence in the simulated response is bolstered by satellite estimates of the Earth's radiative imbalance, which strongly constrain the magnitude of ocean cooling and agree closely with simulated fluxes. Confidence in the ability of the LE to capture fundamental features of the eruption is therefore high.
Figure 31: Simulated sea level rise contributions during and following the eruption of Mt Pinatubo (image credit: NCAR study team)
Legend to Figure 31: Shown are changes in (A) clear-sky albedo over the tropical oceans (30ºN – 30ºS) as an indicator of the eruption's radiative effects and associated global mean sea level (GMSL) anomalies. In (B) contributions from ocean heat content (OHC) atmospheric water vapor (PW) and terrestrial water storage (TWS) estimated from the LE are shown. The large standard deviation across ensemble members (shaded) highlights the obscuring effect of natural climate variability on the eruption's influence in observations.
Discussion: This assessment of the sea level budget during Mt Pinatubo's 1991 eruption and in the several years thereafter has far reaching implications. First, it suggests that our monitoring of sea level via altimetry began in a highly anomalous environment, one in which OHC had been significantly depressed by the eruption while the offsetting influences of the atmosphere and land surface had largely diminished. As the oceans equilibrated from Pinatubo's initial cooling, the sea level experienced an anomalously rapid rise. It is therefore suggested that the GMSL rise estimated from the past decade is likely to be more representative of the background rate due to climate change than that observed during altimetry's initial decade. The eruption of Pinatubo is therefore also reaffirmed as a contributor to the apparently large shift in the rates of rise between the gauge and altimeter eras, consistent with the findings of previous studies.
The budgets simulated by the LE also have implications for the estimation of acceleration. From them, it is estimated that the rate of rise from 1993–2002 is subject to anomalous contribution of about 5 to 7 mm from the recovery to Pinatubo's oceanic cooling. This contribution therefore likely eclipses the background acceleration inferred from the tide gauge record. Given however that no such major eruption has occurred since 1991, a reasonable expectation is also that an accelerated rate of rise may emerge in the near future, particularly as the influences of climate variability and instrument drift reported in previous studies abate.
An estimate of this near-future GMSL acceleration can be made using LE projections of OHC, TWS, and PW in conjunction with independent estimates of future ice sheet losses (Figures 32 and 33). The estimate suggests that, as discussed above, it is unsurprising that acceleration has yet to be detected given the forced response to Pinatubo and the noise of internal climate variability in both OHC and TWS (shaded regions of Figs 2–4), and potential retrieval biases12. Moreover, the result also demonstrates that as anthropogenic influences continue to increase (as a result of both increasing greenhouse gas concentrations and decreasing anthropogenic aerosol emissions), a detectable acceleration of GMSL rise is likely to emerge as it exceeds the noise of background climate variability (shaded) in the coming years. The main contributor to this acceleration is the accelerated increase in OHC, which is offset somewhat by increasing but secondary influences from atmospheric and terrestrial storage, while a key component of the noise obscuring acceleration is the variability of TWS. Moreover, when the effects of the Mt Pinatubo eruption estimated form the LE are removed (blue), acceleration becomes apparent, even in the present day. The magnitude of the acceleration in the mid-21st century is estimated here to be 0.12 mm yr-2, though this value depends strongly on future ice sheet losses, which are highly uncertain1. Its accurate estimation depends both on the accuracy of altimeter retrievals and our ability to distinguish it from internal variability, which can be pronounced in some years but over the long term becomes increasingly negligible, particularly if acceleration is estimated from the full post-1993 record (red line in Figure 33).
With the launch of Jason-3 earlier this year, it is reasonable to ask what new climate insights the instrument may bring. This analysis concludes that if the lifespan of the instrument is comparable to that of its predecessor, Jason-2, the acceleration suggested in earlier studies will likely emerge from the noise of internal climate variability during its lifetime, barring another major volcanic eruption. Moreover, given the unique strengths of sea level as a stable and holistic measure of climate change, the broader altimeter record is likely to stand as one of the benchmark measures of accelerating changes in the climate system.
Figure 32: Sea level rise associated with ocean heat storage and the sum of all contributions estimated from LE budgets and cryospheric contributions (image credit: NCAR study team)
Legend to Figure 32: Shaded are 1σ (light) and 2σ ranges of internal variability. The mean LE estimate with Pinatubo effects removed is also shown (blue) along with the altimeter record (red).
Figure 33: Estimated acceleration in sea level rise based on the budget from the LE and cryospheric contributions using trend differences 1) between the first and second half of a record beginning in 1993 and ending in a given year (abscissa, red) and 2) for the trailing two decades, based on given end years (abscissa, black), image credit: NCAR study team
Legend to Figure 33: Acceleration with Pinatubo effects removed is also shown (blue). The 2σ spread in simulated acceleration estimates is shown for all contributions (light grey) and the contribution due to TWS alone (dark grey).
Difficulties in making weather measurements in the Arctic have led to underrepresentation of this rapidly warming area in historic temperature records
• July 21, 2016: A new NASA-led study finds that almost one-fifth of the global warming that has occurred in the past 150 years has been missed by historical records due to quirks in how global temperatures were recorded. The study explains why projections of future climate based solely on historical records estimate lower rates of warming than predictions from climate models. 53)
The study applied the quirks in the historical records to climate model output and then performed the same calculations on both the models and the observations to make the first true apples-to-apples comparison of warming rates. With this modification, the models and observations largely agree on expected near-term global warming. The results were published in the journal Nature Climate Change. Mark Richardson of NASA's Jet Propulsion Laboratory, Pasadena, California, is the lead author. 54)
The Arctic is warming faster than the rest of Earth, but there are fewer historic temperature readings from there than from lower latitudes because it is so inaccessible. A data set with fewer Arctic temperature measurements naturally shows less warming than a climate model that fully represents the Arctic. — Because it isn't possible to add more measurements from the past, the researchers instead set up the climate models to mimic the limited coverage in the historical records.
The new study also accounted for two other issues. First, the historical data mix air and water temperatures, whereas model results refer to air temperatures only. This quirk also skews the historical record toward the cool side, because water warms less than air. The final issue is that there was considerably more Arctic sea ice when temperature records began in the 1860s, and early observers recorded air temperatures over nearby land areas for the sea-ice-covered regions. As the ice melted, later observers switched to water temperatures instead. That also pushed down the reported temperature change.
Scientists have known about these quirks for some time, but this is the first study to calculate their impact. "They're quite small on their own, but they add up in the same direction," Richardson said. "We were surprised that they added up to such a big effect."
These quirks hide around 19 percent of global air-temperature warming since the 1860s. That's enough that calculations generated from historical records alone were cooler than about 90 percent of the results from the climate models that the IPCC (Intergovernmental Panel on Climate Change) uses for its authoritative assessment reports. In the apples-to-apples comparison, the historical temperature calculation was close to the middle of the range of calculations from the IPCC's suite of models.
Any research that compares modeled and observed long-term temperature records could suffer from the same problems, Richardson said. "Researchers should be clear about how they use temperature records, to make sure that comparisons are fair. It had seemed like real-world data hinted that future global warming would be a bit less than models said. This mostly disappears in a fair comparison."
Antarctic sea-ice expansion between 2000 and 2014 driven by tropical Pacific decadal climate variability
• July 4, 2016: The recent trend of increasing Antarctic sea ice extent — seemingly at odds with climate model projections — can largely be explained by a natural climate fluctuation, according to a new study led by NCAR (National Center for Atmospheric Research) of Boulder, CO. The study offers evidence that the negative phase of the IPO (Interdecadal Pacific Oscillation), which is characterized by cooler-than-average sea surface temperatures in the tropical eastern Pacific, has created favorable conditions for additional Antarctic sea ice growth since 2000. 55) The findings, published in the journal Nature Geoscience, may resolve a longstanding mystery: Why is Antarctic sea ice expanding when climate change is causing the world to warm? 56)
The study's authors also suggest that sea ice may begin to shrink as the IPO switches to a positive phase. "The climate we experience during any given decade is some combination of naturally occurring variability and the planet's response to increasing greenhouse gases," said NCAR scientist Gerald Meehl, lead author of the study. "It's never all one or the other, but the combination, that is important to understand."
Study co-authors include Julie Arblaster of NCAR and Monash University in Australia, Cecilia Bitz of the University of Washington, Christine Chung of the Australian Bureau of Meteorology, and NCAR scientist Haiyan Teng. The study was funded by the U.S. Department of Energy and by the National Science Foundation, which sponsors NCAR.
The sea ice surrounding Antarctica has been slowly increasing in area since the satellite record began in 1979. But the rate of increase rose nearly five fold between 2000 and 2014, following the IPO transition to a negative phase in 1999.
The new study finds that when the IPO changes phase, from positive to negative or vice versa, it touches off a chain reaction of climate impacts that may ultimately affect sea ice formation at the bottom of the world.
When the IPO transitions to a negative phase, the sea surface temperatures in the tropical eastern Pacific become somewhat cooler than average when measured over a decade or two. These sea surface temperatures, in turn, change tropical precipitation, which drives large-scale changes to the winds that extend all the way down to Antarctica.
The ultimate impact is a deepening of a low-pressure system off the coast of Antarctica known as the Amundsen Sea Low. Winds generated on the western flank of this system blow sea ice northward, away from Antarctica, helping to enlarge the extent of sea ice coverage.
"Compared to the Arctic, global warming causes only weak Antarctic sea ice loss, which is why the IPO can have such a striking effect in the Antarctic," said Bitz. "There is no comparable natural variability in the Arctic that competes with global warming."
Figure 34: On Sept. 19, 2014, the five-day average of Antarctic sea ice extent exceeded 20 million km2 for the first time since 1979, according to the National Snow and Ice Data Center. The red line shows the average maximum extent from 1979-2014 (image credit: NASA's Scientific Visualization Studio, Cindy Starr)
Sifting through simulations:
To test if these IPO-related impacts were sufficient to cause the growth in sea ice extent observed between 2000 and 2014, the scientists first examined 262 climate simulations created by different modeling groups from around the world.
When all of those simulations are averaged, the natural variability cancels itself out. For example, simulations with a positive IPO offset those with a negative IPO. What remains is the expected impact of human-caused climate change: a decline in Antarctic sea ice extent.
But for this study, the scientists were not interested in the average. Instead, they wanted to find individual members that correctly characterized the natural variability between 2000-2014, including the negative phase of the IPO. The team discovered 10 simulations that met the criteria, and all of them showed an increase in Antarctic sea ice extent across all seasons.
"When all the models are taken together, the natural variability is averaged out, leaving only the shrinking sea ice caused by global warming," Arblaster said. "But the model simulations that happen to sync up with the observed natural variability capture the expansion of the sea ice area. And we were able to trace these changes to the equatorial eastern Pacific in our model experiments."
Scientists suspect that in 2014, the IPO began to change from negative to positive. That would indicate an upcoming period of warmer eastern Pacific Ocean surface temperatures on average, though year-to-year temperatures may go up or down, depending on El Niño/La Niña conditions. Accordingly, the trend of increasing Antarctic sea ice extent may also change in response.
"As the IPO transitions to positive, the increase of Antarctic sea ice extent should slow and perhaps start to show signs of retreat when averaged over the next 10 years or so," Meehl said.
Climate Change May Shift or Shrink Penguin Habitat in Antarctica
• July 13, 2016: For thousands of years, spells of warm weather along the coast of Antarctica helped penguin populations thrive. Milder weather meant more bare-rock locations for the birds to lay their eggs and nurture their chicks, as well as less stress on the parents and newborns and less sea ice to fight through in the harbors. But over the past few decades, some parts of the southern continent have turned too warm—particularly the water—due to global climate change. According to a new study, that warmth is likely to change where Adélies can raise chicks. 57)
The contribution of climate change to shifts in a species' geographic distribution is a critical and often unresolved ecological question. Climate change in Antarctica is asymmetric, with cooling in parts of the continent and warming along the West Antarctic Peninsula (WAP). The Adélie penguin (Pygoscelis adeliae) is a circumpolar meso-predator exposed to the full range of Antarctic climate and is undergoing dramatic population shifts coincident with climate change. 58)
Using observations of penguin populations and of environmental conditions, as well as computer models of projected environmental changes, the team of researchers projected that nearly a third of Adélie penguin colonies around Antarctica (representing about 20 percent of the total population) could be in decline by 2060. By the end of the 21st century, as much as 60 percent of the colonies could be in trouble. On the other hand, some new refuges on other parts of the coast could open up and offset the losses.
"It is only in recent decades that we know Adélie penguins population declines are associated with warming, which suggests that many regions of Antarctica have warmed too much and that further warming is no longer positive for the species," said Megan Cimino.
The maps of Figures 35 and 36 were built from previous observations (in-person counts and satellite studies) of penguin populations. Red dots mark colonies that have been declining in population—most notably along the Antarctic Peninsula, one of the fastest-warming places on Earth. Blue dots show the location of growing colonies, which often matches where temperatures have been stable or somewhat cooler. Yellow dots denote stable penguin populations.
Warmer temperatures can open up land-based habitat for the penguins, while also keeping waterways ice-free and making it less arduous to search for food. But those warmer temperatures can also make the waters less hospitable (too warm; too little plankton) for the krill and fish that penguins eat. On the other hand, some coastlines could become more hospitable in the future—warming enough to create more habitat, but not enough to disrupt the food supply. The Cape Adare region on Ross Sea is one such area.
Figure 35: Adélie penguin breeding colonies and population status across Antarctica (image credit: Penguin Science Team)
Legend to Figure 35: Each colored circle represents a colonies' current population trend. The black dashed line separates West Antarctic Peninsula (WAP) from continental Adélie penguin colonies.
Figure 36: This Figure shows the output of "habitat suitability models" in which the science team plugged in data on past conditions around penguin colonies while projecting various scenarios in future water temperatures and sea ice concentration. Shades of red indicate areas where habitat is likely to be less suitable for raising penguin chicks as the world warms; blue areas are likely to become more favorable (image credit: NASA Earth Observatory, Joshua Stevens)
El Niño conditions in 2015 and early 2016 altered rainfall patterns around the world
• July 5, 2016: In the Amazon basin, El Niño reduced rainfall during the wet season, leaving the region drier at the start of the 2016 dry season than any year since 2002. "Severe drought conditions at the start of the dry season have set the stage for extreme fire risk in 2016 across the southern Amazon," said Doug Morton, an Earth scientist at NASA/GSFC (Goddard Space Flight Center) and a co-creator of the fire forecast. The wildfire risk for July to October now exceeds the fire risk in 2005 and 2010—drought years when wildfires burned large swaths of the rainforest. 59)
- The Amazon fire forecast analyzes the relationship between certain climate observations and active fire detections from NASA satellites to predict fire season severity. Developed in 2011 by scientists at the University of California, Irvine (UC Irvine) and NASA, the forecast model is focused particularly on the link between sea surface temperatures and fire activity. Warmer sea surface temperatures in the tropical Pacific (as observed during an El Niño) and Atlantic oceans shift rainfall away from the Amazon region, increasing the risk of fire during dry months.
- The forecast team also tracks changes in water storage during the dry season. The maps of Figure 37 show the accumulated deficit in the rainfall input to surface and underground water storage in 2016 and other recent drought years, as reported by the GPCC (Global Precipitation Climatology Centre). The accumulated deficit is measured from August through May; for example, August 2015 to May 2016 sets the stage for the 2016 dry season. Shades of red depict areas where rainfall has been below normal, while blues were above normal.
- For 2016, El Niño-driven conditions are far drier than in 2005 and 2010—the last years when the region experienced drought. The prediction team has developed a web tool to track the evolution of the fire season in near-real time by Amazon region. Estimated fire emissions from each region are updated daily based on active fire detections—made by the MODIS (Moderate Resolution Imaging Spectroradiometer) instrument on NASA's Terra satellite—and data from previous years in the Global Fire Emissions Database. So far, the region has seen more fires through June 2016 than in previous years, another indicator of a potentially tough season.
- "When trees have less moisture to draw upon at the beginning of the dry season, they become more vulnerable to fire and evaporate less water into the atmosphere," said UC-Irvine scientist Jim Randerson, who collaborated with UC-Irvine scientist Yang Chen on building the forecast model. "This puts millions of trees under stress and lowers humidity across the region, allowing fires to grow bigger than they normally would."
- NASA and UC-Irvine scientists have worked in recent years with South American officials and scientists to make them aware of the forecast. Liana Anderson, a from Brazil's National Center for Monitoring and Early Warning of Natural Disasters, said "fire forecasts three to six months before peak fire activity are important to identify areas with higher fire probability for integrated planning."
- The fire forecast team is also working to improve wildfire forecasts in other regions of the world. The scientists recently identified nine regions outside the Amazon where fire season risk could be forecast three- to six months ahead of peak fire activity. Randerson said it may be possible to build seasonal fire forecasts for much of Central America and for many countries in Southeast Asia.
Figure 37: Fire forecast maps for the Amazon region. The maps show the accumulated deficit in the rainfall input to surface and underground water storage in 2016 and other recent drought years, as reported by the GPCC (image credit: NASA Earth Observatory images by Joshua Stevens, using data courtesy of Yang Chen, University of California Irvine, and the GPCC)
Sea Ice Differences at Earth's Poles
May 2016: Why has the sea ice cover surrounding Antarctica been increasing slightly, in sharp contrast to the drastic loss of sea ice occurring in the Arctic Ocean? A new NASA-led study finds the geology of Antarctica and the Southern Ocean are responsible. 60)
A NASA/NOAA/university team led by Son Nghiem of NASA/JPL (Jet Propulsion Laboratory), Pasadena, California, used satellite radar, sea surface temperature, land form and bathymetry (ocean depth) data to study the physical processes and properties affecting Antarctic sea ice. They found that two persistent geological factors — the topography of Antarctica and the depth of the ocean surrounding it — are influencing winds and ocean currents, respectively, to drive the formation and evolution of Antarctica's sea ice cover and help sustain it. "Our study provides strong evidence that the behavior of Antarctic sea ice is entirely consistent with the geophysical characteristics found in the southern polar region, which differ sharply from those present in the Arctic," said Nghiem.
The Antarctic sea ice cover is dominated by first-year (seasonal) sea ice. Each year, the sea ice reaches its maximum extent around the frozen continent in September and retreats to about 17 percent of that extent in February. Since the late 1970s, its extent has been relatively stable, increasing just slightly; however, regional differences are observed.
Over the years, scientists have floated various hypotheses to explain the behavior of Antarctic sea ice, particularly in light of observed global temperature increases. Are changes in the ozone hole involved? Could fresh meltwater from Antarctic ice shelves be making the ocean surface less salty and more conducive to ice formation, since salt inhibits freezing? Are increases in the strength of Antarctic winds causing the ice to thicken? Something is protecting Antarctic sea ice, but a definitive answer has remained elusive.
To tackle this cryospheric conundrum, Nghiem and his team adopted a novel approach. They analyzed radar data from NASA's QuikSCAT satellite from 1999 to 2009 to trace the paths of Antarctic sea ice movements and map its different types. They focused on the 2008 growth season, a year of exceptional seasonal variability in Antarctic sea ice coverage.
Their analyses revealed that as sea ice forms and builds up early in the sea ice growth season, it gets pushed offshore and northward by winds, forming a protective shield of older, thicker ice that circulates around the continent. The persistent winds, which flow downslope off the continent and are shaped by Antarctica's topography, pile ice up against the massive ice shield, enhancing its thickness. This band of ice, which varies in width from roughly 100 to 1,000 km, encapsulates and protects younger, thinner ice in the ice pack behind it from being reduced by winds and waves.
The team also used QuikSCAT radar data to classify the different types of Antarctic sea ice. Older, thicker sea ice returns a stronger radar signal than younger, thinner ice does. They found the sea ice within the protective shield was older and rougher (due to longer exposure to wind and waves), and thicker (due to more ice growth and snow accumulation). As the sea ice cover expands and ice drifts away from the continent, areas of open water form behind it on the sea surface, creating "ice factories" conducive to rapid sea ice growth.
To address the question of how the Southern Ocean maintains this great sea ice shield, the team combined sea surface temperature data from multiple satellites with a recently available bathymetric chart of the depth of the world's oceans. Sea surface temperature data reveal that at the peak of ice growth season, the boundary of the ice shield remains behind a -1º Celsius temperature line surrounding Antarctica. This temperature line corresponds with the southern Antarctic Circumpolar Current front, a boundary that separates the circulation of cold and warm waters around Antarctica. The team theorized that the location of this front follows the underwater bathymetry.
When they plotted the bathymetric data against the ocean temperatures, the pieces fit together like a jigsaw puzzle. Pronounced seafloor features strongly guide the ocean current and correspond closely with observed regional Antarctic sea ice patterns. For example, the current stays near Bouvet Island, located 1,600 km from the nearest land, where three tectonic plates join to form seafloor ridges. Off the coast of East Antarctica, the -1º Celsius sea surface temperature lines closely bundle together as they cross the Kerguelen Plateau (a submerged microcontinent that broke out of the ancient Gondwana supercontinent), through a deep channel called the Fawn Trough. But those lines spread apart over adjacent deep ocean basins, where seafloor features are not pronounced. Off the West Antarctica coast, the deep, smooth seafloor loses its grip over the current, allowing sea ice extent to decrease and resulting in large year-to-year variations.
The study results are published in the journal Remote Sensing of Environment. 61) Other participating institutions include the Joint Institute for Regional Earth System Science and Engineering at UCLA; the Applied Physics Laboratory at the University of Washington in Seattle; and the U.S. National/Naval Ice Center, NOAA Satellite Operations Facility in Suitland, Maryland. Additional funding was provided by the National Science Foundation.
Figure 38: Location of the southern Antarctic Circumpolar Current front (white contour), with -1º Celsius sea surface temperature lines (black contours) on Sept. 22 each year from 2002-2009, plotted against a chart of the depth of the Southern Ocean around Antarctica (image credit: NASA/JPL-Caltech)
Figure 39: The edge of the protective ice shield is determined by the boundary of the surface temperature being -1ºC; the white cross is Bouvet Island (image credit: NASA/JPL- Caltech)
EO Topics continued
Methane and Carbon Dioxide on the rise in the period 2003-2014
• May 2016: Satellite readings show that atmospheric methane and carbon dioxide are continuing to increase despite global efforts to reduce emissions. Methane concentrations were somewhat constant until 2007, but since then have increased at about 0.3% per year, whereas global carbon dioxide levels continue to rise at about 0.5% per year. The reason for this recent methane increase is not fully understood, but scientists attribute it to several sources such as agriculture and fossil fuels. 62)
The data also show seasonal fluctuations, such as higher concentrations of methane in India and China during August and September. This is because wetlands and rice paddies are a major source of methane and emissions are largest if it is warm and humid. - Other regions such as the Tropics, the USA and parts of Russia experience similar seasonal changes.
Carbon dioxide shows similar seasonal fluctuations, albeit with a maximum concentration earlier in the season at northern latitudes. This is due to the regular uptake and release of carbon dioxide by the growing and decay of terrestrial vegetation: photosynthesis, respiration and decay of organic matter. Overall, carbon dioxide has shown a steady increase over the past decade despite global efforts to reduce emissions.
Currently, plants take up about 25% of the carbon dioxide we are emitting and, without this, atmospheric carbon dioxide levels and related consequences would be much larger," said Michael Buchwitz from the IUP (Institute of Environmental Physics) of the University of Bremen in Germany. "However, we do not know how plants will respond to a changing climate. Our understanding of the ‘land carbon sink' is limited. A goal of the satellite carbon dioxide observations is to close related knowledge gaps, which will lead to improved climate prediction."
The upcoming Sentinel-5P mission(launch scheduled for October 2016) for Europe's Copernicus program is set to continue data collection on methane and other components of atmospheric chemistry by scanning the whole globe every day. "For the future, Sentinel-5P will be very important, in particular because of its very dense, high-resolution observations of atmospheric methane, which have the potential to detect and quantify the emissions of important methane emission hot spots such as oil and gas fields," noted Michael Buchwitz, who also leads the Greenhouse Gases project under ESA's Climate Change Initiative.
The newly released ‘Climate Research Data Package No. 3' covers more than one decade (2003–14) of atmospheric data products used to get information on the sources and sinks of carbon dioxide and methane. 63) The atmospheric data products are available through the GHG-CCI website.64)
GHG-CCI (Green House Gas-Climate Change Initiative): Carbon dioxide (CO2) and methane (CH4) are the two most important anthropogenic greenhouse gases (GHGs). Satellite observations combined with modelling helps to improve our knowledge on CO2 and CH4 sources and sinks as required for better climate prediction. GHG-CCI aims at delivering the high quality satellite retrievals needed for this application.
Figure 40: The maps show atmospheric levels of methane from 2003 to 2005 and 2008 to 2010, showing increased concentrations in the latter dataset (in red), image credit:
Figure 41: Carbon dioxide observed by SCIAMACHY on Envisat and by TANSO-FTS on GOSAT (image credit: GHG-CCI, IUP, Univ. Bremen/SRON/JPL/ESA/DLR)
The timescales of global surface-ocean connectivity
• April 2016: The billions of single-celled marine organisms known as phytoplankton can drift from one region of the world's oceans to almost any other place on the globe in less than a decade, Princeton University researchers have found.- Unfortunately, the same principle can apply to plastic debris, radioactive particles and virtually any other man-made flotsam and jetsam that litter our seas, the researchers found. Pollution can thus become a problem far from where it originated within just a few years. 65) 66)
The finding that objects can move around the globe in just 10 years suggests that ocean biodiversity may be more resilient to climate change than previously thought, according to a study published this week in the journal Nature Communications. Phytoplankton form the basis of the marine food chain, and their rapid spread could enable them to quickly repopulate areas where warming seas or ocean acidification have decimated them.
"Our study shows that the ocean is quite efficient in moving things around," said Bror Fredrik Jönsson, an associate research scholar in Princeton's Department of Geosciences, who conducted the study with co-author James R. Watson, a former Princeton postdoctoral researcher who is now a researcher at Stockholm University. "This comes as a surprise to a lot of people, and in fact we spent about two years confirming this work to make sure we got it right," Jönsson said.
One of the strengths of the model is its approach of following phytoplankton wherever they go throughout the world rather than focusing on their behavior in one region, Jönsson said. Because most marine organisms are mobile, this particle-tracking approach can yield new insights compared to the approach of studying one area of ocean.
The resulting model works for objects that have no ability to control their movement such as phytoplankton, bacteria and man-made debris. Organisms that can control their movement even a small amount — such as zooplankton, which can control their vertical position in water — are not accounted for in the model. Nor does the model apply to objects such as boats that protrude above the water and can be pushed by surface winds.
The team applied a computer algorithm to calculate the fastest route an object can travel via ocean currents between various points on the globe. Most previous studies looked only at movement of phytoplankton within regions. The resulting database, Jönsson said, is analogous to a mileage chart one would find on a roadmap or atlas showing the distance between two cities, except that Jönsson and Watson are indicating the speed of travel between different points.
The researchers confirmed that the travel times calculated by their model were similar to the time it took real objects accidentally dumped into the ocean to be carried by currents. For instance, 29,000 rubber ducks and other plastic bath toys toppled off a Chinese freighter in 1992 and have since been tracked as a method of understanding ocean currents. A similar utility has stemmed from the "Great Shoe Spill of 1990" when more than 60,000 Nike athletic shoes plunged into the ocean near Alaska and have been riding the currents off the Pacific Northwest ever since.
The researchers' model also matched the amount of time it took radioactive particles to reach the West Coast of the United States from Japan's Fukushima I Nuclear Power Plant, which released large amounts of radioactive materials into the Pacific Ocean following heavy damage from a tsunami in March 2011. The actual travel time of the materials was 3.6 years; the model calculated it would take 3.5 years.
Figure 42: Princeton University researchers found that ocean currents can carry objects to almost any place on the globe in less than a decade, faster than previously thought. The model above shows how phytoplankton traveling on ocean currents would spread over a three-year period. The researchers "released" thousands of particles representing phytoplankton and garbage from a starting point (green) stretching north to south from Greenland to the Antarctic Peninsula. The colors to the left indicate low (blue) or high (red) concentration of particles. Over time, the particles spiral out to reach the North and South Pacific, Europe, Africa and the Indian Ocean. (Animation by Bror Jönsson, Department of Geosciences)
To create the model, Jönsson and Watson obtained surface-current data from a database of modeled global surface currents developed at the MIT (Massachusetts Institute of Technology) and housed at NASA's Jet Propulsion Laboratory in California. Into this virtual world, they released thousands of particles that represented phytoplankton and then ran simulations multiple times, comparing past and present runs for accuracy and making tweaks to improve the model. They eventually tracked more than 50 billion positions of particles, which is just a fraction of the actual number of phytoplankton in the ocean.
Because phytoplankton mainly reproduce asexually — meaning that one organism alone can produce offspring — only one individual needs to reach a new area to colonize it. This fact led the team to look at the shortest time it takes to get around the world rather than the average time. "The rule for our phytoplankton was 'drive at fast as possible,'" Jönsson said.
To cut down the computing resources needed to track the particles, the researchers calculated the fastest way to get from one place to another using a shortcut commonly employed by smartphone apps and in-car navigation systems. The method, called "Dijkstra's algorithm" after the late Dutch computer scientist Edsger Dijkstra who developed it in the 1950s, calculates how to get from A to C if you know the route from A to B and B to C. "Dijkstra's algorithm is a way of optimizing for the shortest path between two positions when you have a network of possible locations, and we used it to find pathways when there was no direct link from one region to another," Watson said.
Although each step in the pathway from one region to another may be unlikely, the fact that a single phytoplankton organism, which lives only a few weeks, can give rise to millions of offspring means that even unlikely paths will have some followers.
Professor of Marine Sciences Per Jonsson at the University of Gothenburg Center for Sea and Society in Sweden said that the analysis offers a new perspective on global connectivity. "This is the first attempt to identify time scales of connectivity and possible dispersal barriers for plankton across all oceans," said Jonsson, who had no role in the research and is not related to study author Bror Jönsson. "The general message is that all parts of the ocean surface are connected on surprisingly short time scales.
"This implies that regional declines in plankton fitness due to climate change may be buffered by relatively rapid immigration coupled with community sorting or evolutionary change," Jonsson continued. "The authors also offer a practical and predictive tool for a range of studies regarding global ocean dispersal, including the spread of contaminants and marine litter."
The paper, "The timescales of global surface-ocean connectivity," was published online in-advance-of-print April 19 in the journal Nature Communications. The work was funded in part by the National Science Foundation, NASA and the Nippon Foundation-University of British Columbia's Nereus Program.
Evidence for ice-free summers 6-10 million years ago in the late Miocene central Arctic Ocean
• April 2016: An international team of scientists led by the AWI (Alfred Wegener Institute, Helmholtz Center for Polar and Marine Research) in Bremerhaven, Germany have managed to open a new window into the climate history of the Arctic Ocean. Using unique sediment samples from the Lomonosov Ridge, the researchers found that six to ten million years ago the central Arctic was completely ice-free during summer and sea-surface temperature reached values of 4 -9º Celsius. In spring, autumn and winter, however, the ocean was covered by sea ice of variable extent, the scientists explain in the current issue of the journal Nature Communications. These new findings from the Arctic region provide new benchmarks for ground-truthing global climate reconstructions and modelling.67) 68)
Although the permanently to seasonally ice-covered Arctic Ocean is a unique and sensitive component in the Earth's climate system, the knowledge of its long-term climate history remains very limited due to the restricted number of pre-Quaternary sedimentary records. During Polarstern Expedition PS87/2014. "The Arctic sea ice is a very critical and sensitive component in the global climate system. It is therefore important to better understand the processes controlling present and past changes in sea ice. In this context, one of our expedition's aims was to recover long sediment cores from the central Arctic, that can be used to reconstruct the history of the ocean's sea ice cover throughout the past 50 million years. Until recently, only a very few cores representing such old sediments were available, and, thus, our knowledge of the Arctic climate and sea ice cover several millions of year ago is still very limited," explained Rüdiger Stein, AWI geologist, expedition leader and lead author of the study.
The AWI researchers discovered an ideal place for recovering the sediment cores on the western slope of the Lomonosov Ridge, a large undersea mountain range in the central Arctic. "This slope must have experienced gigantic recurring landslides in the past, which resulted in the exhumation of more than 500 m thick ancient sediment and rock formations. We were also surprised about the wide-spread occurrence of these slide scars, which extend over a length of more than 300 km, almost from the North Pole to the southern end of the ridge on the Siberian side," said Rüdiger Stein.
Within a two-day coring action, Stein and his team took 18 sediment cores from this narrow area on Lomonosov Ridge on board the Polarstern research vessel. Although the recovered sediment cores were only four to eight meter long, one of them turned out to be precisely one of those climate archives that the scientists had been looking for a long time. "With the help of certain microfossils, so-called dinoflagellates, we were able to unambiguously establish that the lower part of this core consists of approximately six to eight million-year-old sediments, thereby tracing its geological history back to the late Miocene. With the help of so-called ‘climate indicators or proxies', this gave us the unique opportunity to reconstruct the climate conditions in the central Arctic Ocean for a time period for which only very vague and contradictory information was available," said Rüdiger Stein.
Some scientists were of the opinion that the central Arctic Ocean was already covered with dense sea ice all year round six to ten million years ago – roughly to the same extent as today. The new research findings contradict this assumption. "Our data clearly indicate that six to ten million years ago, the North Pole and the entire central Arctic Ocean must in fact have been ice-free in the summer," explained Rüdiger Stein.
There is a general consensus that the polar regions—and in particular the Arctic Ocean and surrounding areas—are at present, and were over historic and geologic time scales, subject to rapid and dramatic environmental changes. Owing to complex feedback processes, collectively known as ‘polar amplification', the Arctic is both a contributor to climate change and a region that will be most affected by global warming. Despite the importance of the Arctic Ocean in the global climate system, this permanently to seasonally ice-covered region (Figure 43) is one of the last major physiographic provinces on Earth, whose climate history and its transition from early Cenozoic Greenhouse to late Cenozoic Icehouse conditions remain still poorly known. Only one drill site recovered from the central Arctic Ocean during the ACEX (Arctic Coring Expedition)—the IODP (Integrated Ocean Drilling Program) Expedition 302 in 2004—gives some insight into the early Cenozoic climate (Ref. 68).
Concerning recent climate change, the most prominent example is the dramatic decrease of the extent and thickness of the Arctic sea-ice cover the last decades, a decrease that seems to be by far more rapid than predicted by climate models. The scientific community recognized this drastic change with major concern as the Arctic sea ice is a critical component in the global climate system, which contributes to changes in the Earth's albedo, primary productivity and deep-water formation, a driving mechanism for global thermohaline circulation. The causes of these recent changes, that is, natural versus anthropogenic forcings, and their relevance within the global climate system, however, are subject of intense scientific and societal debate. Thus, understanding the processes controlling Arctic sea-ice variability is of overall interest and significance. In this context, records of past climate and sea-ice conditions going beyond instrumental records and representing times of different boundary conditions are of major value: such records can be used to assess the sensitivity of the Earth‘s climate system to changes of different forcing parameters, for example, level of CO2, and to test the reliability of climate models by evaluating their simulations for conditions very different from the modern climate. This type of records giving detailed information about past Arctic sea-ice conditions are still very rare, especially due to the lack of precise proxies for sea-ice reconstructions.
Here, the project applies the new sea-ice biomarker approach together with alkenone-based SSTs (Sea Surface Temperatures) to sediment cores most recently recovered during Polarstern Expedition PS87, to reconstruct upper Miocene Arctic Ocean sea-ice and SST conditions. The proxy data are combined with climate model simulations using a coupled atmosphere-ocean general circulation model with focus on seasonal changes in the high northern latitudes. Based on our new proxy records, we demonstrate that only a seasonal sea-ice cover has been predominant in the central Arctic Ocean during (most of) the Late Miocene time interval. Furthermore, our combined data/modelling approach seems to indicate either relatively high atmospheric CO2 concentrations and/or an overly weak sensitivity of the model to simulate the magnitude of warm polar temperatures in the late Miocene. These new findings from the Arctic region provide new benchmarks for ground-truthing global climate reconstructions and modelling.
Figure 43: Modern Arctic Ocean SST (Sea Surface Temperature) and sea-ice conditions (image credit: AWI Research Team)
Legend to Figure 43: (a) Map of modern August SST with locations of ODP Site 907, ODP Site 910 and IODP Expedition 302 (ACEX) Site, as well as Core PS87/106 (August SST data—average of 1955–2012—from World Ocean Atlas;). (b) Map of summer sea-ice concentration—average of 1988–2007—with locations of studied sites (black dots). Maps a and b produced with Ocean Data View software (source: https://odv.awi.de/). (c) Generalized scheme illustrating (1) sea surface conditions and respective (spring/summer) productivities of ice algae and phytoplankton, and (2) sedimentary contents of IP25, terrigenous biomarkers and IRD, phytoplankton-derived biomarkers and PIP25 index for different settings in the modern Arctic Ocean. Owing to ice melting and related nutrient and sediment release, a stable ice-edge situation is characterized by high concentrations of IP25 and phytoplankton biomarkers, but also by high concentrations of terrigenous biomarkers and IRD. Modern situations at the locations of ACEX and PS87/106, ODP Site 910 (and close-by ODP sites 911 and 912) and ODP Site 907 are indicated.
Large submarine slide scars along Lomonosov Ridge. Polarstern Expedition PS87 was scheduled for August–September 2014 to explore the Lomonosov Ridge area (Figure 44) with the objective of collecting seismic data and sediment cores to reconstruct the short- and long-term climate history and the tectonic evolution of the central Arctic Ocean. More than 3,000 km of high-quality MCS (Multi-Channel Seismic) profiles and B10,000 km of high-quality multibeam bathymetry and sub-bottom sediment-echosounding (PARASOUND) profiles were acquired along the ship's track and numerous sediment cores were recovered (Figure 44).
One major finding of the expedition was the discovery of numerous submarine slide scars that occurred on both sides of the crest of Lomonosov Ridge over a distance of ca. 350 km between 81º07' N and 84º 14' N in water depths from B800 to 1,500 m (Figure 45a). Single scars are up to several km wide and long, and their head walls are 100-500 m high. Swath-bathymetry data indicate that different processes probably triggered slope failures, that various processes of sediment evacuation took place, and that failures occurred at various times. Slide scars were earlier described from a restricted area on Lomonosov Ridge near 88ºN18. However, the wide lateral distribution of mass wasting as presented here is a new discovery.
On top of the southern Lomonosov Ridge in areas between the slide scars, the team discovered SE–NW oriented, streamlined landforms over distances of 4100 km at water depths between 800 and 1,000 m (Figure 45a). These features are interpreted to be glacial lineations that formed beneath grounded ice. Similar unidirectional bed forms have also been identified further east on the East Siberian continental margin where they were related to large and coherent ice masses ESCIS (East Siberian Chukchi Ice Sheet). The lineations identified in this study are similar to those on the East Siberian continental margin with respect to their orthogonal orientations to the proposed center of the former ESCIS.
At the present state of knowledge, the most plausible glacial scenario is a larger than originally proposed ESCIS including an ice shelf extending into the Arctic Ocean, which formed an ice rise on the Southern Lomonosov Ridge over areas presently shallower than 1,000 m. The load and erosional behavior of this ice rise that probably occurred during extended Quaternary glaciations, for example, during MIS 6 (Marine Isotope Stage 6), may have caused physical conditions that triggered the landslides on this part of the Lomonosov Ridge. A MIS 6 age of this erosional event is in line with the proposed age of a major glaciation with extended ice sheets/shelves in Eurasia and East Siberia.
Figure 44: Cruise track and multibeam bathymetric survey of Polarstern Expedition PS87 (AWI Research Team)
Legend to Figure 44: (a) PS87 cruise track (blue line). AB (Amundsen Basin); AR (Alpha Ridge); GR (Gakkel Ridge); LR (Lomonosov Ridge); MB (Makarov Basin); MR (Mendeleev Ridge); NB (Nansen Basin). Orange circles indicate coring stations, the red asterisk indicates the location of the ACEX Site and the green circle indicates the North Pole (Polarstern reached on 26 August 2014 at 10:23 UTC). (b) Track lines of multibeam bathymetric survey. Color bar indicates water depth in meters (m WD). LR-01A, LR-02A and LORI-05B indicate locations of proposed IODP drill sites51. Areas of Figure 45 a,b are indicated.
Figure 45: Bathymetric and acoustic/seismic profiling records from southern Lomonosov Ridge (AWI Research Team)
Legend to Figure 45: (a) Three-dimensional (3D) image of the swath bathymetry of southern Lomonosov Ridge, showing major slide scars and escarpments, streamlined SE–NW oriented glacial lineations formed beneath grounded ice sheets/streams and transects 1 and 2 with locations of sediment cores. (b) PARASOUND profile across Transect 1 with locations of coring stations. (c) Processed multi-channel seismic profile AWI-20140311 across Transect 1, showing prominent reflectors and age assignments based on correlation between regional seismic lines and well data.
Exhumation of Miocene to lower Quaternary sediments. Sediment removal from the steep slopes of the escarpments exposed older, normally more deeply buried deposits at/near the present seafloor, allowing retrieval of older sediments by gravity coring from Polarstern, rather than expensive drilling. The PARASOUND and MCS profiles suggest that these sedimentary sections are composed of Eocene, Oligocene, Miocene, Pliocene and Quaternary strata (Figure 45 b,c). The age control for the stratigraphic units is based on links of seismic lines to drill site data from the Chukchi Shelf, the ACEX drill site on central Lomonosov Ridge and onshore geology from the New Siberian Islands. After evaluation of the multibeam bathymetry and PARASOUND data, the team selected two transects across the steep western slope of the Lomonosov Ridge for an extensive sediment coring program (Figure 45 a, Transect 1 and Transect 2). In total, 16 sediment cores were recovered from water depths between 900 m (top of Lomonosov Ridge) and 1,500 m (bottom of Lomonosov Ridge), Figure 45 a,b.
Whereas most of the sediment cores of Transect 1 are composed of predominantly upper Quaternary (post slide) deposits, some contain prominent unconformities with lower/pre-Quaternary sediments underneath. At these unconformities, a 50-80 m thick overburden has been removed, as demonstrated in compaction experiments (see ‘Sediment load and compaction experiments'). Unfortunately, the microfossil assemblages (that is,palynomorphs and agglutinated benthic foraminifers) do not allow a precise age determination of the sediments underlying the Quaternary near-surface deposits in most of these cores. The predominance of Quaternary sediments in the cores of Transect 1, however, seems to be supported by the biomarker composition determined in selected cores. Close to zero concentrations or the absence of specific biomarkers indicative for phytoplankton and sea-ice algae productivity point to surface-water conditions similar to those of the central Arctic Ocean during late Quaternary times, characterized by a thick perennial sea-ice cover and SSTs (Sea Surface Temperatures) << 0ºC.
The only core providing a clear indication that old sediments are cropping out near the seafloor is Core PS87/106. In this core recovered at the lower slope at Transect 2 (Figure 45 a), a sharp unconformity or hiatus occurs at 370 cmbsf. This unconformity is characterized by a marked change in color, an abrupt increase in WBD (Wet-Bulk Density); related to enhanced sediment consolidation underneath the hiatus), a significant drop in magnetic susceptibility (MS) and a major change in the biomarker composition, and it separates this interval from the overlying young and unconsolidated (upper Quaternary) sediments (Figure 46).
Figure 46: Proxy evidence from Core PS87/106 for late Miocene Arctic Ocean climate conditions (image credit: AWI Research Team)
Legend to Figure 46: (a) LSI (Line-Scan Image), (b) WBD, (c) MS, (d) alkenone-based SST, (e) concentrations of alkenones, (f) dinosterol and (g) brassicasterol as proxy for primary productivity, (h) concentrations of terrigenous sterols (sum of campesterol and b-sitosterol), (i) concentrations of sea-ice proxy IP25 and (j) sea-ice index PdinoIP25. Purple and open triangles indicate the presence or absence of alkenones, respectively. Green line marks depth of the hiatus. Below the hiatus, sediments are overconsolidated. Zero or near-zero concentrations of IP25 and phytoplankton biomarkers are indicative for a closed (spring) sea-ice cover (PdinoIP25 is indetermable and set to ‘1'; see Figure 43). PIP25 values are used to identify low (0–20%), common (20–50%), ice-edge (50–70%) and extended (>70%) sea-ice concentrations (see Figure 43). The section below the hiatus represents about one cold (‘glacial')–warm (‘interglacial') cycle. S1 and S2 indicate two scenarios of different sea-ice concentrations (that is, maximum and transitional/stable ice edge, respectively) within this climate cycle. The interval between the two dashed horizontal lines marks period with minimum sea-ice cover. Using mean sedimentation rates of ~3.2 cm ky-1 (as calculated independently from close-by gravity cores and seismic data), the duration of the climate cycle is ~40 ky.
Late Miocene SST and sea-ice records. The biomarker data of Core PS87/106 suggest significantly different late Miocene paleoenvironmental conditions in comparison with those predominant during Quaternary times (Figure 46). In the upper Miocene sediments, elevated concentrations of alkenones and alkenone-derived SST between 4 and 7ºC (or even 6–9ºC in case other calibrations are used indicate relatively warm, open-water and productive paleoenvironmental conditions in the central Arctic Ocean during the summer season. This is also supported by SST values of >>0 C determined in some samples from the ACEX Site.
The team's results reveal for the first time the occurrence of the biomarker sea-ice proxy IP25 in sediments as old as late Miocene. This proxy was developed by Belt et al. and was before our study only found in Quaternary and Pliocene sediments. The presence of IP25 in the PS87/106 sediments is indicative for the presence of (spring) sea ice in the late Miocene central Arctic Ocean (Figure 43). In comparison with IP25 values from the Arctic Ocean surface sediments and sediment trap data, the absolute IP25 concentrations ranging between 0.05 and 0.15 µg gOC-1 (Figure 46) are more than one order of magnitude lower. These differences are caused by an early degradation of biomarkers that already starts in the water column and reaches its maximum in the uppermost cm of the sediments. On the other hand, both IP25 and phytoplankton biomarker concentrations determined in Core PS87/106 are in the same range than those determined in early-mid Holocene Arctic sediments.
Using the ‘PIP25 Index' as a more semi-quantitative proxy of paleo-sea-ice cover (Figure 1), the team's data from Core PS87/106 point to a variable spring sea-ice coverage of ~20–70% in the lower part and ~100% in the upper part of the sequence (Figure 46). The combination of IP25 and SST data indicates that the central Arctic Ocean must have been relatively warm and ice-free during summer throughout the time interval recovered in the sedimentary section of Core PS87/106 and variable sea ice must have existed during spring when daylight conditions allowed sea-ice algae production (Figures 43 and 47). Furthermore, this implies the presence of an extended sea-ice cover during the dark, cold winter season. These new data clearly support that periods with only a seasonal sea-ice coverage must have occurred in the central Arctic Ocean during most of the late Miocene (Figure 47).
Figure 47: Schematic illustrations of the seasonal sea-ice cycle during the late Miocene (image credit: AWI Research Team)
Legend to Figure 47: The seasonal sea-ice cycle and related principal processes controlling productivity and carbon flux at location of central Arctic Ocean Core PS87/106 during the late Miocene are shown for two different scenarios. (a) Scenario 2 (‘warmer/transitional situation') =extended period of spring sea-ice algae productivity and increased IP25 and phytoplankton biomarker fluxes. (b) Scenario 1 (‘cold situation') =restricted period of late spring sea-ice algae productivity and very reduced fluxes (almost to zero) of IP25 and spring phytoplankton biomarkers; Figure 43). MIZ (Marginal Ice Zone), that is, ice-edge situation. The dark period, height of the sun and changing thickness of snow and ice over the year, as well as phytoplankton, zooplankton and sea-ice productivity are shown. IP25 values for the different seasons are indicated.
A Global View of Methane
March 2016: For a chemical compound that shows up nearly everywhere on the planet, methane still surprises us. It is one of the most potent greenhouse gases, and yet the reasons for why and where it shows up are often a mystery. What we know for sure is that a lot more methane (CH4) has made its way into the atmosphere since the beginning of the Industrial Revolution. Less understood is why the ebb and flow of this gas has changed in recent decades. 69)
One can find the odorless, transparent gas miles below Earth's surface and miles above it. Methane bubbles up from swamps and rivers, belches from volcanoes, rises from wildfires, and seeps from the guts of cows and termites (where is it made by microbes). Human settlements are awash with the gas. Methane leaks silently from natural gas and oil wells and pipelines, as well as coal mines. It stews in landfills, sewage treatment plants, and rice paddies.
AIRS (Atmospheric Infrared Sounder) aboard NASA's Aqua satellite offers one spaceborne perspective on the methane in Earth's atmosphere. The map of Figure 48 shows global methane concentrations in January 2016 at a pressure of 400 hPa (hectopascal), or roughly 6 km above Earth's surface. Methane concentrations are higher in the northern hemisphere because both natural- and human-caused sources of methane are more abundant there. Since AIRS observed the methane fairly high in the atmosphere, winds may have transported plumes of gas considerable distances from their sources.
Figure 48: The methane data are from the AIRS (Atmospheric Infrared Sounder) on the Aqua mission acquired in the period January 1-31, 2016 and from in situ measurements (image credit: NASA Earth Observatory, Joshua Stephens)
Long-term global perspective of atmospheric methane:
The long-term, global trend for atmospheric methane is clear. The concentration of the gas was relatively steady for hundreds of thousands of years, but then started to increase rapidly around 1750. The reason is simple: increasing human populations since the start of the Industrial Revolution have meant more agriculture, more waste, and more fossil fuel production. Over the same period, emissions from natural sources have stayed about the same. The charts above, based on a combination of historical ice core data and air monitoring instrument data, depict the rate of increase.
Figure 49: Methane concentration (ppb - parts per billion) from 800,000 BC to 2014 AD (image credit: NASA, Joshua Stevens using data from the EPA)
Legend to Figure 49: A combination of historical ice core data and air monitoring instruments reveals a consistent trend: global atmospheric methane concentrations have risen sharply in the past 2000 years
When the focus is just on the past five decades — when modern scientific tools have been available to detect atmospheric methane — there have been fluctuations in methane levels that are harder to explain. Figure 50, based on data collected by NOAA (National Oceanic and Atmospheric Administration), shows variations in the rate of increase in the concentration of methane in the atmosphere between 1984 and 2014.
Figure 50: Annual increase in globally-averaged atmospheric methane (ppb/year)
In 1985, the average methane concentration was 1,620 parts per billion (ppb). By 2015, it had increased to 1,800 ppb. — Before the Industrial Revolution, concentrations held steady at about 700 ppb. — But the rate of increase in recent decades has varied. From the 1980s until 1992, methane was rising about 12 ppb per year. Then came roughly a decade of slower growth at 3 ppb per year. Between 2000 and 2007, atmospheric methane concentrations stabilized. Starting in 2007, they began to rise again and have continued to do so since, increasing at a rate of 6 ppb per year.
Methane Matters: 70)
In recent years, the gas has started to turn up in some surprising places. Nighttime satellite images show points of light—some of them gas flares—in rural parts of North Dakota, Texas, and Colorado. Mysterious craters venting methane have appeared in Siberia's Yamal Peninsula. In October 2014, scientists announced they had discovered satellite signals of a methane hotspot over the Four Corners region of the United States. Radar observations have shown bubbles of methane rising from the depths of the Arctic Ocean. And eye-popping videos on the Internet show scientists lighting methane-rich Alaskan lakes on fire.
Since 2007, methane has been on the rise, and no one is quite sure why. Some scientists think tropical wetlands have gotten a bit wetter and are releasing more gas. Others point to the natural gas fracking boom in North America and its sometimes leaky infrastructure. Others wonder if changes in agriculture may be playing a role. "There is no question that methane is doing some very odd and worrying things," said Euan Nisbet, an atmospheric scientist at Royal Holloway, University of London. The big question is why. Scientists wonder if they will have the right monitoring systems in place to answer that question adequately.
The stakes are high. Global temperatures in 2014 and 2015 were warmer than at any other time in the modern temperature record, which dates back to 1880. The most recent decade was the warmest on the record. And carbon emissions are central to that rise.
Figure 51: Both years of 2014 and 2015 set records for the warmest temperatures recorded globally. The long term trend also shows that El Niño years are typically warmer than other years image credit: NASA Earth Observatory, image by Joshua Stevens, using data from the NASA Goddard Institute for Space Studies)
Methane makes up just 0.00018 percent of the atmosphere, compared to 0.039 percent for carbon dioxide (CO2 is roughly 200 times more abundant) .Yet scientists attribute about one-sixth of recent global warming to methane emissions; what methane lacks in volume it makes up for in potency. Over a 20-year period, one ton of methane has a global warming potential that is 84 to 87 times greater than carbon dioxide. Over a century, that warming potential is 28 to 36 times greater. The difference occurs because methane is mostly scrubbed out of the air by chemical reactions within about ten years, while carbon dioxide persists in the atmosphere for much longer than a century.
"That means the climate effects of methane are front-loaded," explained Drew Shindell, a climate scientist at Duke University. "Part of the reason there is so much interest in methane right now is because reducing those emissions could slow warming over the next few decades. This does not let us off the hook for reducing carbon dioxide, but the benefits of carbon dioxide reductions will come much later."
February 2016: Decade of rising seas slowed by land soaking up extra water
• Feb. 12, 2016: New measurements from the GRACE (Gravity Recovery And Climate Experiment) satellite, an international cooperative US-German dual-minisatellite SST (Satellite-to-Satellite Tracking) geodetic mission, have allowed researchers to identify and quantify, for the first time, how climate-driven increases of liquid water storage on land have affected the rate of sea level rise.
A new study by scientists at NASA/JPL (Jet Propulsion Laboratory) in Pasadena, California, and the University of California, Irvine, shows that while ice sheets and glaciers continue to melt, changes in weather and climate over the past decade have caused Earth's continents to soak up and store an extra 3.2 trillion tons of water in soils, lakes and underground aquifers, temporarily slowing the rate of sea level rise by about 20%.
The water gains over land were spread globally, but taken together they equal the volume of Lake Huron, the world's seventh largest lake. The study is published in the Feb. 12 issue of the journal Science. 71) 72) 73)
Each year, a large amount of water evaporates from the ocean, falls over land as rain or snow, and returns to the ocean through runoff and river flows. This is known as the global hydrologic, or water, cycle. Scientists have long known small changes in the hydrologic cycle — by persistent regional changes in soil moisture or lake levels, for instance — could change the rate of sea level rise from what we would expect based on ice sheet and glacier melt rates. However, they did not know how large the land storage effect would be because there were no instruments that could accurately measure global changes in liquid water on land.
The study team used gravity measurements made between 2002 and 2014 by the GRACE (Gravity Recovery And Climate Experiment) mission to quantify variations in groundwater storage. Combining those data with estimates of mass loss by glaciers revealed groundwater's impact on sea-level change. Net groundwater storage has been increasing, and the greatest regional changes, both positive and negative, are associated with climate-driven variability in precipitation. Thus, groundwater storage has slowed the rate of recent sea-level rise by roughly 15%.
"These [gravity field] changes are often caused by the movement of water – and the measurements are actually quite precise," said John Reager of NASA/JPL." An important piece of this study was making sure that we could reduce the uncertainty in the measurement enough to be able to draw these conclusions. This is the first paper to really reduce the uncertainty enough that we could make a statement about what's happening with glaciers and hydrology together, and we needed a lot of expertise to do that – this project had contributions from experts in hydrology, glaciology, geodesy and atmospheric science."
Over the last two decades, sea level has risen at around 3.2 mm per year, roughly double the average rate for the past century, as oceans warm and glaciers and ice sheets melt. From 2003 to 2011 sea-level rise slowed to around 2.4 mm per year, despite increased melting of glaciers and ice sheets. Many see land water storage – in snow, surface water, soil moisture and groundwater, but not glaciers – as one of the most important yet most uncertain contributions to sea-level trends. The latest IPCC (Intergovernmental Panel on Climate Change) report did not include climate-driven changes in land water storage, through variations in rainfall, evaporation and runoff, because of the challenge of measurement.
The study team used estimates of glacier loss and groundwater depletion to separate the GRACE measurements of global changes in surface mass into components for glaciers, direct human-driven land water storage and climate-driven water storage.
Humans can alter land water storage by extracting groundwater, irrigation, using reservoirs, draining wetland and destroying forest. Such activities are estimated to have caused 0.38 mm of sea-level rise per year from 1993 to 2010, around 15–25% of the sea-level rise observed from the addition of water to the oceans.
Figure 52: Trends in land water storage from GRACE observations, April 2002 to November 2014 (image credit: NASA/JPL Study Team)
Legend to Figure 52: Glaciers and ice sheets are excluded. Shown are the global map (gigatons per year per 1/2-degree grid), zonal total trends, full time series (mm/year SLE), and best-fit linear regression with climatology removed (mm/year SLE). The strongest gains and losses are associated with climate-driven variability in precipitation. Note: SLE (Sea Level Equivalent), TWS (Terrestrial Water Storage).
Figure 53: Storage trends partitioned into hydrologic gains and losses. Left: As in Figure 52, but separated by negative (top) and positive (bottom) land water storage trends. Middle: The zonal average of the negative (top) and positive (bottom) trend map (gigatons per year per 1/2-degree grid). Right: GRACE land water storage time series averaged for the negative (top) and positive (bottom) land water storage trend map (climatology removed), image credit: NASA/JPL Study Team
Every year, land temporarily stores then releases a net 6000 ± 1400 Gt (gigtons) of mass through the seasonal cycling of water, which is equivalent to an oscillation in sea level of 17 ± 4 mm. Thus, natural changes in interannual to decadal cycling and storage of water from oceans to land and back can have a large effect on the rate of SLR (Sea Level Rise) on decadal intervals. From 2003 to 2011, SLR slowed to a rate of ~2.4 mm/year during a period of increased mass loss from glaciers and ice sheets. Climate-driven changes in land water storage have been suggested to have contributed to this slowdown, but this assertion has not been verified with direct observations.
Until recently, little data have existed to constrain land water storage contributions to global mean SLR. As a result, this term has either been excluded from SLR budgets or has been approximated by using ad hoc accounting that includes modeling or scaling of a variety of ground-based observations. Human-induced changes in land water storage (hereafter referred to as "human-driven land water storage") include the direct effects of groundwater extraction, irrigation, impoundment in reservoirs, wetland drainage, and deforestation. These activities may play a major role in modulating rates of sea level change, and several studies of large aquifers suggest that trends in regional and global land water storage are now strongly influenced by the effects of groundwater withdrawal. Currently, human activity (including groundwater depletion and reservoir impoundment) is estimated to have directly resulted in a net 0.38 ± 0.12mm/year SLE (Sea Level Equivalent) between 1993 and 2010 or 15 to 25% of observed barystatic SLR, but estimates are acknowledged to have large uncertainties.
Figure 54: Observed global mass contributions to SLR, 2002 to 2014, including the disaggregated land water storage term.(Left: Global mass contributions to sea level from GRACE mascons, including total ocean mass change (1.58 mm year-1 SLE), partitioned between contributions from Greenland (0.77 mm year-1 SLE), Antarctica (0.49 mm year-1 SLE), and net LWS (Land Water Storage) of 0.32 mm year-1 SLE. Right: Disaggregation of net LWS contributions, including the estimate of land glacier losses (0.65 mm year-1) anthropogenic hydrology (0.38mm year-1), and climate-driven land water storage from this study (-0.71 mm year-1).
Table 2: Estimates of net direct-human water management contributions to SLR from previous studies. The range of estimates results from different methodological approaches and assumptions, including modeling, remote sensing, and ground-based methods. To achieve a net human-driven contribution, the IPCC AR5 applied an estimate of reservoir retention to the average of the Konikow (14) and Wada (13) groundwater depletion estimates. 74) 75) 76) 77) 78) 79)
NASA, NOAA Analyses Reveal Record Warm Temperatures in 2015
• January 20, 2016: Earth's 2015 surface temperatures were the warmest since modern record keeping began in 1880, according to independent analyses by NASA and NOAA (National Oceanic and Atmospheric Administration). Globally-averaged temperatures in 2015 shattered the previous mark set in 2014 by 0.13º Celsius. Only once before, in 1998, has the new record been greater than the old record by this much. 80) 81)
Figure 55: 2015 was the warmest year since modern record-keeping began in 1880, according to a new analysis by NASA's Goddard Institute for Space Studies. The record-breaking year continues a long-term warming trend — 15 of the 16 warmest years on record have now occurred since 2001 (image credit: Scientific Visualization Studio/Goddard Space Flight Center)
The 2015 temperatures continue a long-term warming trend, according to analyses by scientists at NASA's GISS (Goddard Institute for Space Studies) in New York (GISTEMP). NOAA scientists agreed with the finding that 2015 was the warmest year on record based on separate, independent analyses of the data. Because weather station locations and measurements change over time, there is some uncertainty in the individual values in the GISTEMP index. Taking this into account, NASA analysis estimates 2015 was the warmest year with 94% certainty.
"Climate change is the challenge of our generation, and NASA's vital work on this important issue affects every person on Earth," said NASA Administrator Charles Bolden. "Today's announcement not only underscores how critical NASA's Earth observation program is, it is a key data point that should make policy makers stand up and take notice - now is the time to act on climate."
The planet's average surface temperature has risen about 1.0 degree Celsius since the late-19th century, a change largely driven by increased carbon dioxide and other human-made emissions into the atmosphere. Most of the warming occurred in the past 35 years, with 15 of the 16 warmest years on record occurring since 2001. Last year was the first time the global average temperatures were 1º Celsius or more above the 1880-1899 average.
Phenomena such as El Niño or La Niña, which warm or cool the tropical Pacific Ocean, can contribute to short-term variations in global average temperature. A warming El Niño was in effect for most of 2015. "2015 was remarkable even in the context of the ongoing El Niño," said GISS Director Gavin Schmidt. "Last year's temperatures had an assist from El Niño, but it is the cumulative effect of the long-term trend that has resulted in the record warming that we are seeing."
Weather dynamics often affect regional temperatures, so not every region on Earth experienced record average temperatures last year. For example, NASA and NOAA found that the 2015 annual mean temperature for the contiguous 48 United States was the second warmest on record.
NASA's analyses incorporate surface temperature measurements from 6,300 weather stations, ship- and buoy-based observations of sea surface temperatures, and temperature measurements from Antarctic research stations. These raw measurements are analyzed using an algorithm that considers the varied spacing of temperature stations around the globe and urban heating effects that could skew the conclusions if left unaccounted for. The result is an estimate of the global average temperature difference from a baseline period of 1951 to 1980. - NOAA scientists used much of the same raw temperature data, but a different baseline period, and different methods to analyze Earth's polar regions and global temperatures.
GISS is a NASA laboratory managed by the Earth Sciences Division of the agency's Goddard Space Flight Center in Greenbelt, Maryland. The laboratory is affiliated with Columbia University's Earth Institute and School of Engineering and Applied Science in New York.
NASA monitors Earth's vital signs from land, air and space with a fleet of satellites, as well as airborne and ground-based observation campaigns. The agency develops new ways to observe and study Earth's interconnected natural systems with long-term data records and computer analysis tools to better see how our planet is changing. NASA shares this unique knowledge with the global community and works with institutions in the United States and around the world that contribute to understanding and protecting our home planet.
Figure 56: 2015 by the month - 10 of 2015's monthly global temperatures tied or broke existing records (image credit: NOAA Global Temp)
Climate Change Warming World's Lakes
• December 2015: Climate change is rapidly warming lakes around the world, threatening freshwater supplies and ecosystems, according to a new NASA and NSF (National Science Foundation)-funded study of more than half of the world's freshwater supply.82)
Using more than 25 years of satellite temperature data and ground measurements of 235 lakes on six continents, this study — the largest of its kind — found lakes are warming an average of 0.34º Celsius per decade. The scientists say this is greater than the warming rate of either the ocean or the atmosphere, and it can have profound effects.
The research, published in Geophysical Research Letters, was announced at the American Geophysical Union meeting in San Francisco in December 2015. 83)
As warming rates increase over the next century, algal blooms, which can rob water of oxygen, are projected to increase 20 percent in lakes. Algal blooms that are toxic to fish and animals are expected to increase by 5 percent. Emissions of methane, a greenhouse gas 25 times more powerful than carbon dioxide on 100-year time scales, will increase 4 percent over the next decade, if these rates continue.
"Society depends on surface water for the vast majority of human uses," said co-author Stephanie Hampton, director of Washington State University's Center for Environmental Research, Education and Outreach in Pullman. "Not just for drinking water, but manufacturing, for energy production, for irrigation of our crops. Protein from freshwater fish is especially important in the developing world."
Water temperature influences a host of its other properties critical to the health and viability of ecosystems. When temperatures swing quickly and widely from the norm, life forms in a lake can change dramatically and even disappear. "These results suggest that large changes in our lakes are not only unavoidable, but are probably already happening," said lead author Catherine O'Reilly, associate professor of geology at Illinois State University, Normal, IL. Earlier research by O'Reilly has seen declining productivity in lakes with rising temperatures.
Study co-author Simon Hook, science division manager at NASA/JPL ( Jet Propulsion Laboratory) in Pasadena, California, said satellite measurements provide a broad view of lake temperatures over the entire globe. But they only measure surface temperature, while ground measurements can detect temperature changes throughout a lake. Also, while satellite measurements go back 30 years, some lake measurements go back more than a century. "Combining the ground and satellite measurements provides the most comprehensive view of how lake temperatures are changing around the world," he said.
Figure 57: Global changes in lake temperatures over the past 25 years. Red shades indicate warming; blue shades indicate cooling. The study found Earth's lakes are warming about 0.61 degrees Fahrenheit (0.34 degrees Celsius) per decade on average, faster than overall warming rates for the ocean and atmosphere (image credit: Illinois State University, USGS/California, University of Pennsylvania)
Various climate factors are associated with the warming trend. In northern climates, lakes are losing their ice cover earlier in the spring and many areas of the world have less cloud cover, exposing their waters more to the sun's warming rays.
Previous work by Hook, using satellite data, indicated many lake temperatures were warming faster than air temperature and that the greatest warming was observed at high latitudes, as seen in other climate warming studies. This new research confirmed those observations, with average warming rates of 1.3º Fahrenheit (0.72º Celsius) per decade at high latitudes.
Warm-water tropical lakes may be seeing less dramatic temperature increases, but increased warming of these lakes still can have significant negative impacts on fish. That can be particularly important in the African Great Lakes, where fish are a major source of food. In general, the researchers write, "The pervasive and rapid warming observed here signals the urgent need to incorporate climate impacts into vulnerability assessments and adaptation efforts for lakes."
Figure 58: This image of Lake Tahoe, from the ASTER instrument on Terra, shows the lake's temperature variations (cold is blue, warm is red), image credit: NASA
Figure 59: A combination of satellite data and ground measurements, such as from instrumented buoys like this one in Lake Tahoe on the California/Nevada border, were used to provide a comprehensive view of changing lake temperatures worldwide. The buoy measures the water temperature from above and below. image credit: Limnotech)
Human Fingerprint on Global Air Quality
• December 14, 2015: Using new, high-resolution global satellite maps of air quality indicators, NASA scientists tracked air pollution trends over the last decade in various regions and 195 cities around the globe. According to recent NASA research findings, the United States, Europe and Japan have improved air quality thanks to emission control regulations, while China, India and the Middle East, with their fast-growing economies and expanding industry, have seen more air pollution. 84)
Scientists examined observations made from 2005 to 2014 by the Ozone Monitoring Instrument aboard NASA's Aura satellite. One of the atmospheric gases the instrument detects is nitrogen dioxide, a yellow-brown gas that is a common emission from cars, power plants and industrial activity. Nitrogen dioxide can quickly transform into ground-level ozone, a major respiratory pollutant in urban smog. Nitrogen dioxide hotspots, used as an indicator of general air quality, occur over most major cities in developed and developing nations.
The following visualizations include two types of data. The absolute concentrations show the concentration of tropospheric nitrogen dioxide (Figures 60, 62, 63 and 64), with blue and green colors denoting lower concentrations and orange and red areas indicating higher concentrations.
The second type of data is the trend data from 2005 to 2014 (Figures 65 and 67), which shows the observed change in concentration over the ten-year period. Blue indicated an observed decrease in nitrogen dioxide, and orange indicates an observed increase. Please note that the range on the color bars (text is in white) changes from location to location in order to highlight features seen in the different geographic regions.
Bryan Duncan and his team at NASA/GSFC examined observations made from 2005 to 2014 by the Dutch-Finnish Ozone Monitoring Instrument aboard NASA's Aura satellite. One of the atmospheric gases the instrument detects is nitrogen dioxide, a yellow-brown gas that is a common emission from cars, power plants and industrial activity. Nitrogen dioxide can quickly transform into ground-level ozone, a major respiratory pollutant in urban smog. Nitrogen dioxide hotspots, used as an indicator of general air quality, occur over most major cities in developed and developing nations. 85)
The science team analyzed year-to-year trends in nitrogen dioxide levels around the world. To look for possible explanations for the trends, the researchers compared the satellite record to information about emission controls regulations, national gross domestic product and urban growth. "With the new high-resolution data, we are now able to zoom down to study pollution changes within cities, including from some individual sources, like large power plants," said Duncan.
Previous work using satellites at lower resolution missed variations over short distances. This new space-based view offers consistent information on pollution for cities or countries that may have limited ground-based air monitoring stations. The resulting trend maps tell a unique story for each region.
The United States and Europe are among the largest emitters of nitrogen dioxide. Both regions also showed the most dramatic reductions between 2005 and 2014. Nitrogen dioxide has decreased from 20 to 50 percent in the United States, and by as much as 50 percent in Western Europe. Researchers concluded that the reductions are largely due to the effects of environmental regulations that require technological improvements to reduce pollution emissions from cars and power plants.
China, the world's growing manufacturing hub, saw an increase of 20 to 50 percent in nitrogen dioxide, much of it occurring over the North China Plain. Three major Chinese metropolitan areas — Beijing, Shanghai, and the Pearl River Delta — saw nitrogen dioxide reductions of as much as 40 percent.
The South African region encompassing Johannesburg and Pretoria has the highest nitrogen dioxide levels in the Southern Hemisphere, but the high-resolution trend map shows a complex situation playing out between the two cities and neighboring power plants and industrial areas.
In the Middle East, increased nitrogen dioxide levels since 2005 in Iraq, Kuwait and Iran likely correspond to economic growth in those countries. However, in Syria, nitrogen dioxide levels decreased since 2011, most likely because of the civil war, which has interrupted economic activity and displaced millions of people.
Figure 60: This global map shows the concentration of nitrogen dioxide in the troposphere as detected by the Ozone Monitoring Instrument aboard the NASA Aura satellite, averaged over 2014 (image credit: NASA/GSFC)
Figure 62: This global map shows the concentration of nitrogen dioxide in the atmosphere as detected by the Ozone Monitoring Instrument aboard the NASA Aura satellite, averaged over 2005 (image credit: NASA/GSFC)
Figure 63: Nitrogen dioxide concentrations across the United States, averaged over 2014 (image credit: NASA/GSFC)
Figure 64: Nitrogen dioxide concentrations across the United States, averaged over 2005 (image credit: NASA/GSFC)
Figure 65: The trend map of the United States shows the large decreases in nitrogen dioxide concentrations from 2005 to 2014. Only decreases are highlighted in this map (image credit: NASA/GSFC)
Figure 66: Color bar for the trend in nitrogen dioxide concentrations changes across the United Sates
Figure 67: The trend map of Europe shows the change in nitrogen dioxide concentrations from 2005 to 2014 (image credit: NASA/GSFC)
Figure 68: Color bar for the trend in nitrogen dioxide concentrations changes across Europe (image credit: NASA/GSFC)
In Greenland, another major glacier comes undone
• November, 2015: One of Greenland's glaciers is losing five billion tons of ice a year to the ocean, according to researchers. While these new findings may be disturbing, they are reinforced by a concerted effort to map changes in ice sheets with different sensors from space agencies around the world. It is estimated that the entire Zachariae Isstrom glacier in northeast Greenland holds enough water to raise the global sea levels by more than 46 cm. 86) 87) 88)
- Jeremie Mouginot, from UCI (University of California Irvine), USA and lead author of the paper published in the journal Science, said, "The shape and dynamics of Zachariae Isstrom have changed dramatically over the last few years. The glacier is now breaking up and calving high volumes of icebergs into the ocean, which will result in rising sea levels for decades to come." Mouginot and his colleagues from NASA/JPL and the University of Kansas, Lawrence, set out to study the changes taking place at Zachariae Isstrom.
- As one of the first regions to experience and visibly demonstrate the effects of climate change, the Arctic serves as a barometer for change in the rest of the world. It is therefore critical that polar ice is monitored comprehensively and in a sustained manner. - The value of international organizations joining forces to understand aspects of our planet such as this cannot be underestimated.
- These current findings are a prime example of how different satellite observations and measurements from aerial surveys are being used from various space agencies including ESA (European Space Agency), CSA (Canadian Space Agency), NASA (National Aeronautics and Space Administration), DLR (German Aerospace Center), JAXA (Japan Aerospace Exploration Agency) and Italy's space agency, ASI (Agenzia Spaziale Italiana).
- Over the last nine years the Polar Space Task Group has been coordinating the collection of radar data over Greenland and Antarctica. ESA radar observations going back to the ERS and Envisat satellites through to Sentinel-1A were used in the new study. In addition, the group relied heavily on data from Canada's RADARSAT-1 and -2, Germany's TerraSAR-X and TanDEM-X, Japan's ALOS and Italy's Cosmo-SkyMed constellation to ensure a continuous record of ice-sheet changes through to the launch of Sentinel-1A.
- Using these many sources, scientists determined that the bottom of Zachariae Isstrom is being rapidly eroded by warmer ocean water mixed with growing amounts of meltwater from the ice sheet surface. Jeremie Mouginot said, "Ocean warming has likely played a major role in triggering the glacier's retreat, but we need more oceanographic observations in this critical sector of Greenland to determine its future."
Figure 69: Ice velocity map (magnitude, in logarithmic scale) of the Greenland Ice Sheet derived from SAR data of the Sentinel-1A satellite, acquired in Interferometric Wide Swath Mode (IW) between January and March 2015 (color scale in meters per day), image credit: ESA .
Legend to Figure 69: This map of Greenland ice sheet velocity was created using data from Sentinel-1A in January–March 2015 and complemented by the routine 12-day repeat acquisitions of the margins since June 2015. About 1200 radar scenes from the satellite's wide-swath mode were used to produce the map, which clearly shows dynamic glacier outlets around the Greenland coast. In particular, the Zachariae Isstrom glacier in the northeast is changing rapidly, and recently reported as having become unmoored from a stabilizing sill and now crumbling into the North Atlantic Ocean.
The Sentinel-1 map of the surface velocity is displayed in north polar stereographic projection centered on Greenland, with an origin at 90°N, 45°W, a standard parallel of 70°N, and a reference to the WGS84 ellipsoid, corresponding to the projection used for the GIMP DEM. Figure 69 shows the magnitude of the horizontal surface velocity. The velocity mosaic provides near complete coverage of the ice sheet areas west of the main ice divide. Some gaps exist in the interior eastern and southeastern sections of the ice sheet. The terminus sections of all outlet glaciers are covered. Whereas on outlet glaciers the matching signal for offset tracking is based primarily on amplitude features related to surface structure and roughness, distinct amplitude features are sparse in the interior of the ice sheet and stable speckle patterns are required for correlation of image chips. Preservation of speckle requires temporal coherence. In areas exposed to high snowfall and strong winds the temporal decorrelation of the phase signal limits the availability of suitable repeat pass pairs. Most of the gaps in the January to March, 2015 data set could be filled with additional S-1 data acquisition during the following months.
On some tracks, in particular in the northern section, stripes are evident being aligned approximately perpendicular to the satellite flight direction. These patterns are due to azimuth shifts induced by fluctuations in ionospheric electron density. The ionosphere-induced noise is mainly of relevance for slow motion areas. It can be efficiently reduced by merging velocity data of multiple tracks.
Seven Case Studies in Carbon and Climate
• November 2015: Every part of the mosaic of Earth's surface — ocean and land, Arctic and tropics, forest and grassland — absorbs and releases carbon in a different way. Wild-card events such as massive wildfires and drought complicate the global picture even more. To better predict future climate, we need to understand how Earth's ecosystems will change as the climate warms and how extreme events will shape and interact with the future environment. Here are seven pressing concerns.89)
1) The Arctic:
The Far North is warming twice as fast as the rest of Earth, on average. With a 5-year Arctic airborne observing campaign just wrapping up and a 10-year campaign just starting that will integrate airborne, satellite and surface measurements, NASA is using unprecedented resources to discover how the drastic changes in Arctic carbon are likely to influence our climatic future.
Wildfires have become common in the North. Because firefighting is so difficult in remote areas, many of these fires burn unchecked for months, throwing huge plumes of carbon into the atmosphere. A recent report found a nearly 10-fold increase in the number of large fires in the Arctic region over the last 50 years, and the total area burned by fires is increasing annually.
Organic carbon from plant and animal remains is preserved for millennia in frozen Arctic soil, too cold to decompose. Arctic soils known as permafrost contain more carbon than there is in Earth's atmosphere today. As the frozen landscape continues to thaw, the likelihood increases that not only fires but decomposition will create Arctic atmospheric emissions rivaling those of fossil fuels. The chemical form these emissions take — carbon dioxide or methane — will make a big difference in how much greenhouse warming they create.
Initial results from NASA's CARVE (Carbon in Arctic Reservoirs Vulnerability Experiment) airborne campaign have allayed concerns that large bursts of methane, a more potent greenhouse gas, are already being released from thawing Arctic soils. CARVE principal investigator Charles Miller of NASA/JPL (Jet Propulsion Laboratory), Pasadena, California, is looking forward to NASA's ABoVE (Arctic Boreal Vulnerability Experiment) field campaign to gain more insight. "CARVE just scratched the surface, compared to what ABoVE will do," Miller said.
Figure 70: Runoff in Alaska (image credit: NOAA)
Methane (CH4) is the Billy the Kid of carbon-containing greenhouse gases: it does a lot of damage in a short life. There's much less of it in Earth's atmosphere than there is carbon dioxide, but molecule for molecule, it causes far more greenhouse warming than CO2 does over its average 10-year life span in the atmosphere.
Methane is produced by bacteria that decompose organic material in damp places with little or no oxygen, such as freshwater marshes and the stomachs of cows. Currently, over half of atmospheric methane comes from human-related sources, such as livestock, rice farming, landfills and leaks of natural gas. Natural sources include termites and wetlands. Because of increasing human sources, the atmospheric concentration of methane has doubled in the last 200 years to a level not seen on our planet for 650,000 years.
Locating and measuring human emissions of methane are significant challenges. NASA's Carbon Monitoring System is funding several projects testing new technologies and techniques to improve our ability to monitor the colorless gas and help decision makers pinpoint sources of emissions. One project, led by Daniel Jacob of Harvard University, used satellite observations of methane to infer emissions over North America. The research found that human methane emissions in eastern Texas were 50 to 100 percent higher than previous estimates. "This study shows the potential of satellite observations to assess how methane emissions are changing," said Kevin Bowman, a JPL research scientist who was a coauthor of the study.
3) Tropical Forests:
Tropical forests are carbon storage heavyweights. The Amazon in South America alone absorbs a quarter of all carbon dioxide that ends up on land. Forests in Asia and Africa also do their part in "breathing in" as much carbon dioxide as possible and using it to grow.
However, there is evidence that tropical forests may be reaching some kind of limit to growth. While growth rates in temperate and boreal forests continue to increase, trees in the Amazon have been growing more slowly in recent years. They've also been dying sooner. That's partly because the forest was stressed by two severe droughts in 2005 and 2010 — so severe that the Amazon emitted more carbon overall than it absorbed during those years, due to increased fires and reduced growth. Those unprecedented droughts may have been only a foretaste of what is ahead, because models predict that droughts will increase in frequency and severity in the future.
In the past 40-50 years, the greatest threat to tropical rainforests has been not climate but humans, and here the news from the Amazon is better. Brazil has reduced Amazon deforestation in its territory by 60 to 70 percent since 2004, despite troubling increases in the last three years. According to Doug Morton, a scientist at NASA's Goddard Space Flight Center in Greenbelt, Maryland, further reductions may not make a marked difference in the global carbon budget. "No one wants to abandon efforts to preserve and protect the tropical forests," he said. "But doing that with the expectation that [it] is a meaningful way to address global greenhouse gas emissions has become less defensible."
In the last few years, Brazil's progress has left Indonesia the distinction of being the nation with the highest deforestation rate and also with the largest overall area of forest cleared in the world. Although Indonesia's forests are only a quarter to a fifth the extent of the Amazon, fires there emit massive amounts of carbon, because about half of the Indonesian forests grow on carbon-rich peat. A recent study estimated that this fall, daily greenhouse gas emissions from recent Indonesian fires regularly surpassed daily emissions from the entire United States.
Wildfires are natural and necessary for some forest ecosystems, keeping them healthy by fertilizing soil, clearing ground for young plants, and allowing species to germinate and reproduce. Like the carbon cycle itself, fires are being pushed out of their normal roles by climate change. Shorter winters and higher temperatures during the other seasons lead to drier vegetation and soils. Globally, fire seasons are almost 20 percent longer today, on average, than they were 35 years ago.
Currently, wildfires are estimated to spew 2 to 4 billion tons of carbon into the atmosphere each year on average — about half as much as is emitted by fossil fuel burning. Large as that number is, it's just the beginning of the impact of fires on the carbon cycle. As a burned forest regrows, decades will pass before it reaches its former levels of carbon absorption. If the area is cleared for agriculture, the croplands will never absorb as much carbon as the forest did.
As atmospheric carbon dioxide continues to increase and global temperatures warm, climate models show the threat of wildfires increasing throughout this century. In Earth's more arid regions like the U.S. West, rising temperatures will continue to dry out vegetation so fires start and burn more easily. In Arctic and boreal ecosystems, intense wildfires are burning not just the trees, but also the carbon-rich soil itself, accelerating the thaw of permafrost, and dumping even more carbon dioxide and methane into the atmosphere.
5) North American Forests:
With decades of Landsat satellite imagery at their fingertips, researchers can track changes to North American forests since the mid-1980s. A warming climate is making its presence known.
Through the North American Forest Dynamics project, and a dataset based on Landsat imagery released this earlier this month, researchers can track where tree cover is disappearing through logging, wildfires, windstorms, insect outbreaks, drought, mountaintop mining, and people clearing land for development and agriculture. Equally, they can see where forests are growing back over past logging projects, abandoned croplands and other previously disturbed areas.
"One takeaway from the project is how active U.S. forests are, and how young American forests are," said Jeff Masek of Goddard, one of the project's principal investigators along with researchers from the University of Maryland and the U.S. Forest Service. In the Southeast, fast-growing tree farms illustrate a human influence on the forest life cycle. In the West, however, much of the forest disturbance is directly or indirectly tied to climate. Wildfires stretched across more acres in Alaska this year than they have in any other year in the satellite record. Insects and drought have turned green forests brown in the Rocky Mountains. In the Southwest, pinyon-juniper forests have died back due to drought.
Scientists are studying North American forests and the carbon they store with other remote sensing instruments. With radars and lidars, which measure height of vegetation from satellite or airborne platforms, they can calculate how much biomass — the total amount of plant material, like trunks, stems and leaves — these forests contain. Then, models looking at how fast forests are growing or shrinking can calculate carbon uptake and release into the atmosphere. An instrument planned to fly on the ISS (International Space Station), called the GEDI (Global Ecosystem Dynamics Investigation) lidar, will measure tree height from orbit, and a second ISS mission called the ECOSTRESS (Ecosystem Spaceborne Thermal Radiometer Experiment on Space Station) will monitor how forests are using water, an indicator of their carbon uptake during growth. Two other upcoming radar satellite missions (the NASA-ISRO SAR radar, or NISAR, and the European Space Agency's BIOMASS radar) will provide even more complementary, comprehensive information on vegetation.
6) Ocean Carbon Absorption:
When carbon-dioxide-rich air meets seawater containing less carbon dioxide, the greenhouse gas diffuses from the atmosphere into the ocean as irresistibly as a ball rolls downhill. Today, about a quarter of human-produced carbon dioxide emissions get absorbed into the ocean. Once the carbon is in the water, it can stay there for hundreds of years.
Warm, CO2-rich surface water flows in ocean currents to colder parts of the globe, releasing its heat along the way. In the polar regions, the now-cool water sinks several miles deep, carrying its carbon burden to the depths. Eventually, that same water wells up far away and returns carbon to the surface; but the entire trip is thought to take about a thousand years. In other words, water upwelling today dates from the Middle Ages - long before fossil fuel emissions.
That's good for the atmosphere, but the ocean pays a heavy price for absorbing so much carbon: acidification. Carbon dioxide reacts chemically with seawater to make the water more acidic. This fundamental change threatens many marine creatures. The chain of chemical reactions ends up reducing the amount of a particular form of carbon — the carbonate ion — that these organisms need to make shells and skeletons. Dubbed the "other carbon dioxide problem," ocean acidification has potential impacts on millions of people who depend on the ocean for food and resources.
Microscopic, aquatic plants called phytoplankton are another way that ocean ecosystems absorb carbon dioxide emissions. Phytoplankton float with currents, consuming carbon dioxide as they grow. They are at the base of the ocean's food chain, eaten by tiny animals called zooplankton that are then consumed by larger species. When phytoplankton and zooplankton die, they may sink to the ocean floor, taking the carbon stored in their bodies with them.
Satellite instruments like MODIS (Moderate resolution Imaging Spectroradiometer) on NASA's Terra and Aqua spacecraft let us observe ocean color, which researchers can use to estimate abundance — more green equals more phytoplankton. But not all phytoplankton are equal. Some bigger species, like diatoms, need more nutrients in the surface waters. The bigger species also are generally heavier so more readily sink to the ocean floor.
As ocean currents change, however, the layers of surface water that have the right mix of sunlight, temperature and nutrients for phytoplankton to thrive are changing as well. "In the Northern Hemisphere, there's a declining trend in phytoplankton," said Cecile Rousseaux, an oceanographer with the Global Modeling and Assimilation Office at Goddard. She used models to determine that the decline at the highest latitudes was due to a decrease in abundance of diatoms. One future mission, the PACE (Pre-Aerosol, Clouds, and ocean Ecosystem) satellite, will use instruments designed to see shades of color in the ocean — and through that, allow scientists to better quantify different phytoplankton species.
In the Arctic, however, phytoplankton may be increasing due to climate change. The NASA-sponsored ICESCAPE (Impacts of Climate on the Eco-Systems and Chemistry of the Arctic Pacific Environment) expedition on a U.S. Coast Guard icebreaker in 2010 and 2011 found unprecedented phytoplankton blooms under about three feet (a meter) of sea ice off Alaska. Scientists think this unusually thin ice allows sunlight to filter down to the water, catalyzing plant blooms where they had never been observed before.
Mass Gains of Antarctic Ice Sheet Greater than Losses
• In October 2015, a new NASA study says that an increase in Antarctic snow accumulation that began 10,000 years ago is currently adding enough ice to the continent to outweigh the increased losses from its thinning glaciers. The research challenges the conclusions of other studies, including the IPCC (Intergovernmental Panel on Climate Change) 2013 report, which says that Antarctica is overall losing land ice. 90) 91)
According to the new analysis of satellite data, the Antarctic ice sheet showed a net gain of 112 billion tons of ice a year from 1992 to 2001. That net gain slowed to 82 billion tons of ice per year between 2003 and 2008.
"We're essentially in agreement with other studies that show an increase in ice discharge in the Antarctic Peninsula and the Thwaites and Pine Island region of West Antarctica," said Jay Zwally, a glaciologist with NASA Goddard Space Flight Center in Greenbelt, Maryland, and lead author of the study, which was published on Oct. 30 in the Journal of Glaciology. "Our main disagreement is for East Antarctica and the interior of West Antarctica – there, we see an ice gain that exceeds the losses in the other areas." Zwally added that his team "measured small height changes over large areas, as well as the large changes observed over smaller areas."
Scientists calculate how much the ice sheet is growing or shrinking from the changes in surface height that are measured by the satellite altimeters. In locations where the amount of new snowfall accumulating on an ice sheet is not equal to the ice flow downward and outward to the ocean, the surface height changes and the ice-sheet mass grows or shrinks.
But it might only take a few decades for Antarctica's growth to reverse, according to Zwally. "If the losses of the Antarctic Peninsula and parts of West Antarctica continue to increase at the same rate they've been increasing for the last two decades, the losses will catch up with the long-term gain in East Antarctica in 20 or 30 years — I don't think there will be enough snowfall increase to offset these losses."
The study analyzed changes in the surface height of the Antarctic ice sheet measured by radar altimeters on two ESA (European Space Agency) ERS-1 and -2 (European Remote Sensing) satellites, spanning from 1992 to 2001, and by the laser altimeter on NASA's ICESat (Ice, Cloud, and land Elevation Satellite) from 2003 to 2008.
Zwally said that while other scientists have assumed that the gains in elevation seen in East Antarctica are due to recent increases in snow accumulation, his team used meteorological data beginning in 1979 to show that the snowfall in East Antarctica actually decreased by 11 billion tons per year during both the ERS and ICESat periods. They also used information on snow accumulation for tens of thousands of years, derived by other scientists from ice cores, to conclude that East Antarctica has been thickening for a very long time. "At the end of the last Ice Age, the air became warmer and carried more moisture across the continent, doubling the amount of snow dropped on the ice sheet," Zwally said.
The extra snowfall that began 10,000 years ago has been slowly accumulating on the ice sheet and compacting into solid ice over millennia, thickening the ice in East Antarctica and the interior of West Antarctica by an average of 1.7 cm per year. This small thickening, sustained over thousands of years and spread over the vast expanse of these sectors of Antarctica, corresponds to a very large gain of ice – enough to outweigh the losses from fast-flowing glaciers in other parts of the continent and reduce global sea level rise.
To help accurately measure changes in Antarctica, NASA is developing the successor to the ICESat mission, ICESat-2, which is scheduled to launch in 2018. "ICESat-2 will measure changes in the ice sheet within the thickness of a No. 2 pencil," said Tom Neumann, a glaciologist at Goddard and deputy project scientist for ICESat-2. "It will contribute to solving the problem of Antarctica's mass balance by providing a long-term record of elevation changes."
Figure 71: The map is showing the rates of mass changes from ICESat 2003-2008 over Antarctica. Sums are for all of Antarctica: East Antarctica (EA, 2-17); interior West Antarctica (WA2, 1, 18, 19, and 23); coastal West Antarctica (WA1, 20-21); and the Antarctic Peninsula (24-27). A gigaton (Gt) corresponds to a billion metric tons (image credit:Jay Zwally, Journal of Glaciology)
Antarctic ozone hole nears record size again in 2015
• In October 2015, the ozone hole over Antarctica currently extends over 26 million km2 – an area larger than the North American continent. Currently, it is approximately 2.5 millionkm2 larger than at the same time in 2014. In 2006 it was larger than now, at 27 million km2. Researchers from the German Aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt; DLR) Earth Observation Center (EOC) have discovered this trend using Earth observation satellites. They continuously monitor the protective ozone layer and analyze the changes they observe. 92)
Figure 72: The Antarctic ozone hole (false color view), as observed by the GOME-2 instrument on the MetOp spacecraft of EUMETSAT on October 2, 2015, appears as a nearly circular area (image credit: DLR)
Legend to Figure 72: The ozone concentrations are measured in Dobson units. If all the ozone molecules in the atmosphere were brought to the ground level, for example, an ozone concentration of 200 Dobson units would correspond to a layer thickness of only 2 mm. This shows that ozone is ,in fact, found only in trace amounts in the atmosphere - that is, it is a 'trace gas'. Small amounts of this trace gas can have a large impact, in the same way that a little salt in a soup can significantly affect the flavor.
Intense ozone depletion over Antarctica is a phenomenon that recurs annually. In the stratosphere, at an altitude of between 10 - 50 km, the concentration of chlorofluorocarbons (CFCs) becomes enriched while low temperatures prevail during the southern hemisphere winter. Currently, in the southern hemisphere is springtime, additional sunlight causes these substances to exert their ozone-depleting effect. For this reason, the ozone hole reaches its maximum annual expansion during the spring months in the southern hemisphere and then reduces in size again in the local late spring. In recent years, the ozone hole appeared to have stabilized, suggesting a very gradual recovery of the ozone layer. This year, however, the ozone hole has formed one month later and is now almost as large as it was nine years ago.
Figure 73: This image shows the areal extent of the ozone hole as detected by the DLR WDC-RSAT (World Data Center-Remote Sensing of the Atmosphere) in Oberpfaffenhofen, using daily satellite measurements. The ozone hole formed remarkably late in 2015 - during the last third of August (bold red line). Then in September, it reached an area the size of the North American continent. The magnitude of this expansion is the second largest measured until now. Only in 2006, the ozone hole was larger by about 1 million km2 than this year (image credit: DLR)
The 2015 Arctic Sea Ice Summertime Minimum Is Fourth Lowest on Record
• September 2015: According to a NASA analysis of satellite data, the 2015 Arctic sea ice minimum extent is the fourth lowest on record since observations from space began. The analysis by NASA and the NASA-supported NSIDC (National Snow and Ice Data Center) at the University of Colorado in Boulder showed the annual minimum extent was 4.41 million km2 on Sept. 11,2015. This year's minimum is 1.81 million km2 lower, than the 1981-2010 average. 93)
The Arctic sea ice cover, made of frozen seawater that floats on top of the ocean, helps regulate the planet's temperature by reflecting solar energy back to space. The sea ice cap grows and shrinks cyclically with the seasons. Its minimum summertime extent, which occurs at the end of the melt season, has been decreasing since the late 1970s in response to warming temperatures.
In some recent years, low sea-ice minimum extent has been at least in part exacerbated by meteorological factors, but that was not the case this year. "This year is the fourth lowest, and yet we haven't seen any major weather event or persistent weather pattern in the Arctic this summer that helped push the extent lower as often happens," said Walt Meier, a sea ice scientist with NASA's Goddard Space Flight Center in Greenbelt, Maryland. "It was a bit warmer in some areas than last year, but it was cooler in other places, too."
Figure 74: The 2015 Arctic sea ice summertime minimum is 1.81 million km2 below the 1981-2010 average, shown here as a gold line (image credit: NASA/GSFC Scientific Visualization Studio)
In contrast, the lowest year on record, 2012, saw a powerful August cyclone that fractured the ice cover, accelerating its decline. — The sea ice decline has accelerated since 1996. The 10 lowest minimum extents in the satellite record have occurred in the last 11 years. The 2014 minimum was 5.03 million km2, the seventh lowest on record. Although the 2015 minimum appears to have been reached, there is a chance that changing winds or late-season melt could reduce the Arctic extent even further in the next few days.
This year, the Arctic sea ice cover experienced relatively slow rates of melt in June, which is the month the Arctic receives the most solar energy. However, the rate of ice loss picked up during July, when the sun is still strong. Faster than normal ice loss rates continued through August, a transition month when ice loss typically begins to slow. A big "hole" appeared in August in the ice pack in the Beaufort and Chukchi seas, north of Alaska, when thinner seasonal ice surrounded by thicker, older ice melted. The huge opening allowed for the ocean to absorb more solar energy, accelerating the melt.
It's unclear whether this year's strong El Niño event, which is a naturally occurring phenomenon that typically occurs every two to seven years where the surface water of the eastern equatorial Pacific Ocean warms, has had any impact on the Arctic sea ice minimum extent.
Figure 75: Different projection of the minimum Arctic sea ice extend on Sept. 11, 2015, using data from the AMSR-2 instrument on GCOM-W1. The yellow outline on the map shows the median sea ice extent observed in September from 1981 through 2010 (image credit: NASA Earth Observatory, Jesse Allen) 94)
Long-term trend (14 years) of Carbon Monoxide Measurements from MOPITT on Terra
• June 2, 2015: Carbon monoxide is perhaps best known for the lethal effects it can have in homes with faulty appliances and poor ventilation. In the United States, the colorless, odorless gas kills about 430 people each year. However, the importance of carbon monoxide (CO) extends well beyond the indoor environment. Indoors or outdoors, the gas can disrupt the transport of oxygen by the blood, leading to heart and health problems. CO also contributes to the formation of tropospheric ozone, another air pollutant with unhealthy effects. And though carbon monoxide does not cause climate change directly, its presence affects the abundance of greenhouse gases such as methane and carbon dioxide. 95)
- Carbon monoxide forms whenever carbon-based fuels — including coal, oil, natural gas, and wood — are burned. As a result, many human activities and inventions emit carbon monoxide, including: the combustion engines in cars, trucks, planes, ships, and other vehicles; the fires lit by farmers to clear forests or fields; and industrial processes that involve the combustion of fossil fuels. In addition, wildfires and volcanoes are natural sources of the gas.
- Little was known about the global distribution of carbon monoxide until the launch of the Terra satellite in 1999. Terra carries a sensor MOPITT (Measurements of Pollution in the Troposphere) that can measure carbon monoxide in a consistent fashion on a global scale. With a swath width of 640 km, MOPITT scans the entire atmosphere of Earth every three days.
- Since CO has a lifetime in the troposphere of about one month, it persists long enough to be transported long distances by winds, but not long enough to mix evenly throughout the atmosphere. As a result, MOPITT's maps show significant geographic variability and seasonality. To view month by month maps of carbon monoxide, visit the carbon monoxide page in Earth Observatory's global maps section.
- In Africa, for example, agricultural burning shifts north and south of the equator with the seasons, leading to seasonal shifts in carbon monoxide. Fires are also the dominant source of carbon monoxide pollution in South America and Australia. In the United States, Europe, and eastern Asia, the highest carbon monoxide concentrations occur around urban areas and tend to be a result of vehicle and industrial emissions. However, wildfires burning over large areas in North America, Russia, and China also can be an important source.
- Terra has been in orbit long enough to observe significant changes over time. To illustrate how global carbon monoxide concentrations have changed, maps of the mission's first (2000) and most recent full year (2014) of data are shown in Figure 76. The maps depict yearly average concentrations of tropospheric carbon monoxide at an altitude of 3,700 meters (12,000 feet). Concentrations are expressed in parts per billion by volume (ppbv). A concentration of 1 ppbv means that for every billion molecules of gas in a measured volume, one of them is a carbon monoxide molecule. Yellow areas have little or no carbon monoxide, while progressively higher concentrations are shown in orange and red. Places where data was not available are gray. For both years, the data has been averaged, which eliminates seasonal variations.
- According to MOPITT, carbon monoxide concentrations have declined since 2000 (Figure 76). The decrease is particularly noticeable in the Northern Hemisphere. Most air quality experts attribute the decline to technological and regulatory innovations that mean vehicles and industries are polluting less than they once did. Interestingly, while MOPITT observed slight decreases of carbon monoxide over China and India, satellites and emissions inventories have shown that other pollutants like sulfur dioxide and nitrogen dioxide have risen during the same period.
- "For China, nitrogen dioxide emissions are mostly from the power and transportation sectors and have grown significantly since 2000 with the increase in demand for electricity," explained Helen Worden, an atmospheric scientist from the National Center for Atmospheric Research (NCAR). "Carbon monoxide emissions, however, have a relatively small contribution (less than 2 percent) from the power sector, so vehicle emissions standards and improved combustion efficiency for newer cars have lowered carbon monoxide in the atmosphere despite the fact that there are more vehicles on the road burning more fossil fuel."
- As illustrated by the maps, the news is also generally positive for the Southern Hemisphere, where deforestation and agricultural fires are the primary source of carbon monoxide. In South America, MOPITT observed a slight decrease in carbon monoxide; other satellites have observed decreases in the number of small fires and areas burned, suggesting a decrease in deforestation fires since 2005. Likewise, MOPITT has observed decreases in the amount of carbon monoxide over Africa. "There have been fewer fires in Africa, so that is a big part of the story there," explained Worden. "However, growing cities might be increasing of the amount of CO in some areas of equatorial Africa."
- The line graph of Figure 77 shows the long-term trend as well as monthly variations in carbon monoxide concentrations. While the overall trend is downward, several peaks and valleys are visible. For instance, some researchers attribute the peak from around 2002 to 2003 to an unusually active fire season in the boreal forests of Russia. The dip in carbon monoxide emissions from 2007 to 2009 also matches a decline in global fire emissions. In addition, researchers have noted that this dip overlaps with a global financial crisis that started in late 2008 and caused global manufacturing output to decline.
Figure 76: Earth's CO concentration acquired with MOPITT on Terra in 2000 (top) and in 2014 (bottom), image credit: NASA Earth Observatory, Jesse Allen and Joshua Stevens
Figure 77: Long-term CO concentration trend and monthly variations as measured by MOPITT (image credit: NASA Earth Observatory, Jesse Allen and Joshua Stevens)
2014 — Warmest Year in Modern Record
The year 2014 ranks as Earth's warmest since 1880, according to two separate analyses by NASA and NOAA (National Oceanic and Atmospheric Administration) scientists. 96)
The 10 warmest years in the instrumental record, with the exception of 1998, have now occurred since 2000. This trend continues a long-term warming of the planet, according to an analysis of surface temperature measurements by scientists at NASA's GISS (Goddard Institute of Space Studies) in New York. In an independent analysis of the raw data, also released on Jan. 16, 2015, NOAA scientists also found 2014 to be the warmest on record.
Since 1880, Earth's average surface temperature has warmed by about 0.8º Celsius, a trend that is largely driven by the increase in carbon dioxide (CO2) and other human emissions into the planet's atmosphere. The majority of that warming has occurred in the past three decades.
Figure 78: This color-coded map displays the global temperature anomaly data from 2014 (image credit: NASA/GSFC)
For understanding climate change, the long-term trend of rising temperatures across the planet is more important than any year's individual ranking. These rankings can be sensitive to analysis methods and sampling. While 2014 ranks as the warmest year in NASA's global temperature record, it is statistically close to the values from 2010 and 2005, the next warmest years.
While 2014 temperatures continue the planet's long-term warming trend, scientists still expect to see year-to-year fluctuations in average global temperature caused by phenomena such as El Niño or La Niña. These phenomena warm or cool the tropical Pacific and are thought to have played a role in the flattening of the long-term warming trend over the past 15 years. However, 2014's record warmth occurred during an El Niño-neutral year.
Regional differences in temperature are more strongly affected by weather dynamics than the global mean. For example, in the U.S. in 2014, parts of the Midwest and East Coast were unusually cool, while Alaska and three western states – California, Arizona and Nevada – experienced their warmest year on record, according to NOAA.
GISS (Goddard Institute of Space Studies) is a NASA laboratory managed by the Earth Sciences Division of the agency's Goddard Space Flight Center, in Greenbelt, Maryland. The laboratory is affiliated with Columbia University's Earth Institute and School of Engineering and Applied Science in New York. 97)
The GISS analysis incorporates surface temperature measurements from 6,300 weather stations, ship- and buoy-based observations of sea surface temperatures, and temperature measurements from Antarctic research stations. This raw data is analyzed using an algorithm that takes into account the varied spacing of temperature stations around the globe and urban heating effects that could skew the calculation. The result is an estimate of the global average temperature difference from a baseline period of 1951 to 1980.
• June 9, 2015: NASA has released data showing how temperature and rainfall patterns worldwide may change through the year 2100 because of growing concentrations of greenhouse gases in Earth's atmosphere. The dataset, which is available to the public, shows projected changes worldwide on a regional level in response to different scenarios of increasing carbon dioxide simulated by 21 climate models. The high-resolution data, which can be viewed on a daily timescale at the scale of individual cities and towns, will help scientists and planners conduct climate risk assessments to better understand local and global effects of hazards, such as severe drought, floods, heat waves and losses in agriculture productivity. 98)
- "NASA is in the business of taking what we've learned about our planet from space and creating new products that help us all safeguard our future," said Ellen Stofan, NASA chief scientist. "With this new global dataset, people around the world have a valuable new tool to use in planning how to cope with a warming planet."
- The new dataset is the latest product from NEX (NASA Earth Exchange), a big-data research platform within the NASA Advanced Supercomputing Center at the agency's ARC (Ames Research Center) in Moffett Field, California. In 2013, NEX released similar climate projection data for the continental United States that is being used to quantify climate risks to the nation's agriculture, forests, rivers and cities.
- "This is a fundamental dataset for climate research and assessment with a wide range of applications," said Ramakrishna Nemani, NEX project scientist at Ames. "NASA continues to produce valuable community-based data products on the NEX platform to promote scientific collaboration, knowledge sharing, and research and development."
- This NASA dataset integrates actual measurements from around the world with data from climate simulations created by the international Fifth Coupled Model Intercomparison Project. These climate simulations used the best physical models of the climate system available to provide forecasts of what the global climate might look like under two different greenhouse gas emissions scenarios: a "business as usual" scenario based on current trends and an "extreme case" with a significant increase in emissions.
- The NASA climate projections provide a detailed view of future temperature and precipitation patterns around the world at a 25 km resolution, covering the time period from 1950 to 2100. The 11 TB dataset provides daily estimates of maximum and minimum temperatures and precipitation over the entire globe.
- NEX is a collaboration and analytical platform that combines state-of-the-art supercomputing, Earth system modeling, workflow management and NASA remote-sensing data. Through NEX, users can explore and analyze large Earth science data sets, run and share modeling algorithms and workflows, collaborate on new or existing projects and exchange workflows and results within and among other science communities.
- NEX data and analysis tools are available to the public through the OpenNEX project on Amazon Web Services. OpenNEX is a partnership between NASA and Amazon, Inc., to enhance public access to climate data, and support planning to increase climate resilience in the U.S. and internationally. OpenNEX is an extension of the NASA Earth Exchange in a public cloud-computing environment.
- NASA uses the vantage point of space to increase our understanding of our home planet, improve lives, and safeguard our future. NASA develops new ways to observe and study Earth's interconnected natural systems with long-term data records. The agency freely shares this unique knowledge and works with institutions around the world to gain new insights into how our planet is changing.
Figure 79: The new NASA global data set combines historical measurements with data from climate simulations using the best available computer models to provide forecasts of how global temperature (shown here) and precipitation might change up to 2100 under different greenhouse gas emissions scenarios (image credit: NASA)
• October 2014: Sunlight is the primary driver of Earth's climate and weather. Averaged over the entire planet, roughly 340 W/m2 of energy from the Sun reach Earth. About one-third of that energy is reflected back into space, and the remaining 240 W/m2 is absorbed by land, ocean, and atmosphere. Exactly how much sunlight is absorbed depends on the reflectivity of the atmosphere and the surface.99)
As scientists work to understand why global temperatures are rising and how carbon dioxide and other greenhouse gases are changing the climate system, they have been auditing Earth's energy budget. Is more energy being absorbed by Earth than is being lost to space? If so, what happens to the excess energy?
For seventeen years, scientists have been examining this balance sheet with a series of space-based sensors known as CERES (Clouds and the Earth's Radiant Energy System). The instruments use scanning radiometers to measure both the shortwave solar energy reflected by the planet (albedo) and the longwave thermal energy emitted by it. The first CERES went into space in 1997 on the TRMM (Tropical Rainfall Measuring Mission), and three more have gone up on Terra, Aqua, and Suomi-NPP. The last remaining CERES instrument will fly on the JPSS-1 (Joint Polar Satellite System-1) satellite (launch in 2017), and a follow-on, the RBI (Radiation Budget Instrument), will fly on JPSS-2 (launch in 2022).
Figure 80: Earth's albedo measured with CERES on Terra over the period March 1, 2000 to December 31, 2011 (image credit: NASA, Robert Simon, Mike Carlowicz)
If Earth was completely covered in ice, its albedo would be about 0.84, meaning it would reflect most (84%) of the sunlight that hit it. On the other hand, if Earth was covered by a dark green forest canopy, the albedo would be about 0.14 (most of the sunlight would get absorbed). Changes in ice cover, cloudiness, airborne pollution, or land cover (from forest to farmland, for instance) all have subtle effects on global albedo. Using satellite measurements accumulated since the late 1970s, scientists estimate Earth's average albedo is about about 0.30.
The maps of Figure 80 show how the reflectivity of Earth—the amount of sunlight reflected back into space—changed between March 1, 2000, and December 31, 2011. This global picture of reflectivity (also called albedo) appears to be a muddle, with different areas reflecting more or less sunlight over the 12-year record. Shades of blue mark areas that reflected more sunlight over time (increasing albedo), and orange areas denote less reflection (lower albedo).
Taken across the planet, no significant global trend appears. As noted in the anomaly plot of Figure 81, the global albedo rose and fell in different years, but did not necessarily head in either direction for long.
Figure 81: Albedo anomaly plot over a 12 year period (image credit: NASA)
In the maps of Figure 80, however, some regional patterns emerge. At the North Pole, reflectivity decreased markedly, a result of the declining sea ice on the Arctic Ocean and increasing dust and soot on top of the ice. Around the South Pole, reflectivity is down around West Antarctica and up slightly in parts of East Antarctica, but there is no net gain or loss. At the same time, Antarctic sea ice there has been increasing slightly each year.
One of the most compelling parts of the global map is the signature of the ENSO (El Niño–Southern Oscillation) pattern in the Pacific Ocean (right and left ends of the global map in Figure 80). The first seven years of the CERES data record were characterized by relatively weak El Niño events, but this soon gave way to some moderate-to-strong La Niña events in the latter part of the record. La Niña tends to bring more convection and cloudiness over the western Pacific Ocean, while El Niño brings those rain clouds to the central Pacific. In very strong El Niños, the convection can even travel to the eastern Pacific. The map of CERES reflectivity changes shows an increase in reflectivity in the western tropical Pacific (blue patches in the figure) and reduced reflectivity (orange colors) in the central Pacific—patterns consistent with a shift from El Niño to La Niña during the CERES period.
In the early 2000s, after the first few years of Terra-CERES measurements, it appeared that Earth's albedo was declining, a phenomenon that was widely reported in scientific journals and on NASA Earth Observatory. But as more years of data accumulated, and as scientists began to better understand the data, they found that albedo was neither increasing nor declining over time. It was fluctuating a lot by year, though.
"What the results show is that even at global scales, Earth's albedo fluctuates markedly over short time periods due to natural variations in the climate system," said Norman Loeb, CERES principal investigator at NASA/LaRC ( Langley Research Center). Ice cover, cloud cover, and the amount of airborne particles—aerosols from pollution, volcanoes, and dust storms—can change reflectivity on scales from days to years. "We should not get fooled by short-term fluctuations in the data, as a longer record may reverse any short-term trend."
"The results also suggest that in order to confidently detect changes in Earth's albedo above natural variability, a much longer record is needed," Loeb added. "It is paramount that we continue the CERES Terra, Aqua, and Suomi-NPP observations as long as possible, and launch follow-on Earth radiation budget instruments to ensure continued coverage of this fundamental property of the climate system."
Sea ice retreat in the Arctic and sea ice advancement in the Antarctic as of 2014:
• September 2014: Arctic sea ice coverage continued its below-average trend this year as the ice declined to its annual minimum on Sept. 17, according to the NASA-supported NSIDC (National Snow and Ice Data Center) at the University of Colorado, Boulder, CO. Over the 2014 summer, arctic sea ice melted back from its maximum extent reached in March 2014 to a coverage area of 5.02 million km2 , according to analysis from NASA and NSIDC scientists. This year's minimum extent is similar to last year's and below the 1981-2010 average of 6.22 million km2). 100) 101) 102)
Arctic sea ice coverage in 2014 is the sixth lowest recorded since 1978. The summer started off relatively cool, and lacked the big storms or persistent winds that can break up ice and increase melting. This summer, the Northwest Passage above Canada and Alaska remained ice-bound. A finger of open water stretched north of Siberia in the Laptev Sea, reaching beyond 85 degrees north, which is the farthest north open ocean has reached since the late 1970s.
While summer sea ice has covered more of the Arctic in the last two years than in 2012's record low summer, this is not an indication that the Arctic is returning to average conditions. This year's minimum extent remains in line with a downward trend; the Arctic Ocean is losing about 13% of its sea ice per decade.
To measure sea ice extent, scientists include areas that are at least 15% ice-covered. The NASA-developed computer analysis, which is one of several methods scientists use to calculate extent, is based on data from NASA's Nimbus 7 satellite, which operated from 1978 to 1987, and the U.S. Department of Defense's DMSP (Defense Meteorological Satellite Program), which has provided information since 1987.
In addition to monitoring sea ice from space, NASA is conducting airborne field campaigns to track changes in Arctic sea ice and its impact on climate. Operation IceBridge flights have been measuring Arctic sea ice and ice sheets for the past several years during the spring. A new field experiment, ARISE (Arctic Radiation – IceBridge Sea and Ice Experiment), started in September 2014 to explore the relationship between retreating sea ice and the Arctic climate.
Figure 82: Arctic sea ice hit its annual minimum on Sept. 17, 2014. The red line in this image shows the 1981-2010 average minimum extent. The map is based from data of the AMSR2 instrument on the GCOM-W1 satellite of JAXA (Japan Aerospace Exploration Agency), image credit: NASA, NSIDC
Figure 83: Different projection of the minimum Arctic sea ice extend on Sept. 19, 2014. The yellow outline on the map shows the median sea ice extent observed in September from 1981 through 2010 (image credit: NASA Earth Observatory,, Jesse Allen, Ref. 102)
Antarctic sea ice extend:
Meanwhile, sea ice on the other side of the planet was headed in the opposite direction. Figure 84, also based on data from the AMSR2 (Advanced Microwave Scanning Radiometer -2) sensor, shows the Antarctic sea ice on September 17, 2014. While it was not yet possible to determine if the ice had reached its maximum extent for the year, the five-day average had already surpassed 20 million km2.
Figure 84: Antarctic sea ice extend on September 19, 2014. Sea ice around Antarctica has been increasing, but not by much. The overall trend of sea ice expansion in the Antarctic is only one-third of the magnitude of the decrease in arctic sea ice. The yellow outline on the map shows the median sea ice extent observed in September from 1981 through 2010 (image credit: NASA Earth Observatory,, Jesse Allen)
Antarctic sea ice develops and evolves under vastly different circumstances than Arctic sea ice. In the north, sea ice sits in a nearly land-locked ocean, while sea ice in the southern hemisphere exists in the open ocean surrounding an extensive land mass (the Antarctic continent). This geography affects how the ice expands and retreats in response to climate, leading in part to the differing sea ice scenarios at the two poles (Ref. 102).
Another study of long-term sea ice extend was published in December 2014 by Claire Parkinson of NASA/GSFC to create a global picture of sea ice extents and their changes over the 35-yr period 1979–2013. The results yield a global annual sea ice cycle more in line with the high-amplitude Antarctic annual cycle than the lower-amplitude Arctic annual cycle but trends more in line with the high-magnitude negative Arctic trends than the lower-magnitude positive Antarctic trends. 103)
Globally,the monthly sea ice extent reaches a minimum February and a maximum generally in October or November. All 12 months show negative trends over the 35-yr period, with the largest magnitude monthly trend being the September trend, at -68,200 ± 10,500 km2 yr-1 (2..62% ± 0.40%decade-1), and the yearly average trend being -35,000 ± 5,900 km2 yr-1 (-1.47% ± 0.25%decade-1).
Data sources: The data used for this study are from the SMMR (Scanning Multichannel Microwave Radiometer) on the Nimbus-7 satellite of NASA, the SSM/I (Special Sensor Microwave Imager), flown on the DMSP (Defense Meteorological Satellite Program) spacecraft F8, F11 and F13 of DoD, and SSM/IS (SSM/I Sounder) on the DMSP F17 satellite. These datasets begin shortly after the launch of the Nimbus 7 satellite in late October 1978 and continue to the present time (2014). The data from each sensor are mapped onto rectangular grids overlaid on polar stereographic projections with grid squares (or pixels) sized at approximately 25 km x 25 km. Ice concentration, defined as the percent areal coverage of ice, is calculated at each grid square through the NASA Team algorithm, and ice extent is calculated as the sum of the area of grid squares with ice concentration at least 15%.
The passive-microwave data have undergone rigorous intercalibration, first between the SMMR and SSM/I sensors in 1999 and then between the SSM/I and SSM/IS sensors in 2012, to create a homogeneous dataset for long-term trend studies. The resulting intercalibrated datasets are available from the NSIDC (National Snow and Ice Data Center) in Boulder, Colorado, and have been widely used. Most pertinently, Cavalieri and Parkinson (2012) have used the data for hemispheric studies of the Arctic and Antarctic sea ice extents, respectively, for the period November 1978–December 2010.
Results: Adding Arctic and Antarctic sea ice extents month by month for the period November 1978–December 2013 yields a global time series that shows a strong seasonal cycle with minimum global ice extent occurring in February of each year, maximum ice extent occurring in October or November of each year except 1979, and a minor secondary maximum often occurring in the June–July time frame (Figure 85). In the anomalous year 1979, the customary June/July secondary maximum is instead the primary maximum.
Figure 85: Monthly average global sea ice extents, November 1978–December 2013, as derived from satellite passive-microwave data. The February ice extents are marked by crosses, October ice extents by diamonds, November ice extents by squares aligned with the axes, and ice extents for all other months by circles. The x-axis tick marks are at January of each year, and the year labels are centered at the middle of the year (image credit: NASA, Claire Parkinson)
Examining 35 years of sea ice data, Parkinson has shown that increases around Antarctica do not make up for the accelerated Arctic sea ice loss of the last decades. Earth has been shedding sea ice at an average annual rate of 35,000 km2 since 1979 — the equivalent of losing an area of sea ice larger than the state of Maryland every year.
Even though Antarctic sea ice reached a new record maximum in September 2014, global sea ice is still decreasing. That's because the decreases in Arctic sea ice far exceed the increases in Antarctic sea ice. The line graphs of Figure 86 plot the monthly deviations and overall trends in polar sea ice from 1979 to 2013 as measured by satellites. The top line shows the Arctic, the middle shows Antarctica, and the third line shows the global, combined total. The sparklines at the bottom of the graphs show each year separately, enabling month-to-month comparisons across each year. The thickness of each sparkline indicates the overall growth or loss in sea ice globally. The thinning of the sparklines is indicative of the downward trend in total polar sea ice.
Furthermore, the global sea ice loss has accelerated. From 1979 to 1996, the ice loss was 21,500 km2 per year. This rate from 1996 to 2013 was 50,000 km2 lost per year. Annual losses were larger than the states of Vermont and New Hampshire combined.
• March 19, 2015: The sea ice cap of the Arctic appeared to reach its annual maximum winter extent on Feb. 25, according to data from the NASA-supported National Snow and Ice Data Center (NSIDC) at the University of Colorado, Boulder. At 14.54 million km2, this year's maximum extent was the smallest on the satellite record and also one of the earliest. 105)
Arctic sea ice, frozen seawater floating on top of the Arctic Ocean and its neighboring seas, is in constant change: it grows in the fall and winter, reaching its annual maximum between late February and early April, and then it shrinks in the spring and summer until it hits its annual minimum extent in September. The past decades have seen a downward trend in Arctic sea ice extent during both the growing and melting season, though the decline is steeper in the latter.
Figure 87: The 2015 maximum is compared to the 1979-2014 average maximum shown in yellow. A distance indicator shows the difference between the two in the Sea of Okhotsk north of Japan (image credit: NASA)
The main player in the wintertime maximum extent is the seasonal ice at the edges of the ice pack. This type of ice is thin and at the mercy of which direction the wind blows: warm winds from the south compact the ice northward and also bring heat that makes the ice melt, while cold winds from the north allow more sea ice to form and spread the ice edge southward.
Scientifically, the yearly maximum extent is not as interesting as the minimum. It is highly influenced by weather and we're looking at the loss of thin, seasonal ice that is going to melt anyway in the summer and won't become part of the permanent ice cover, according to Walt Meier of NASA/GSFC. With the summertime minimum, when the extent decreases it's because we're losing the thick ice component, and that is a better indicator of warming temperatures.
Global carbon dioxide emissions:
• September 2014: World leaders face multiple barriers in their efforts to reach agreement on greenhouse gas emission policies. And, according to Arizona State University researchers, without globally consistent, independent emissions assessments, climate agreements will remain burdened by errors, self-reporting and the inability to verify emissions progress.
An international research team led by ASU (Arizona State University) scientists has developed a new approach to estimate CO2 emissions from burning fossil fuels – one that provides crucial information to policymakers. Called the FFDAS (Fossil Fuel Data Assimilation System), this new system was used to quantify 15 years of CO2 emissions, every hour, for the entire planet – down to the city scale. Until now, scientists have estimated greenhouse gas emissions at coarser scales or used less reliable techniques. 106) 107) 108)
Figure 88: Global fossil fuel CO2 emissions as represented by the FFDAS (Fossil Fuel Data Assimilation System), image credit: FFDAS research team
The FFDAS uses information from satellite feeds, national fuel accounts and a new global database on power plants to create high-resolution planetary maps. These maps provide a scientific, independent assessment of the planet's greenhouse gas emissions – something policymakers can use and the public can understand.
The research team built upon the previously developed FFDAS for estimating global high-resolution fossil fuel CO2 emissions — improving the underlying observationally based data sources, expanding the approach through treatment of separate emitting sectors, including a new pointwise database of global power plants, and extending the results to cover a 1997 to 2010 time series at a spatial resolution of 0.1°. The long-term trend analysis of the resulting global emissions shows subnational spatial structure in large active economies such as the United States, China, and India. These three countries, in particular, show different long-term trends and exploration of the trends in nighttime lights, and population reveal a decoupling of population and emissions at the subnational level. Analysis of shorter-term variations reveals the impact of the 2008–2009 global financial crisis with widespread negative emission anomalies across the U.S. and Europe (Ref. 108).
The team used a center of mass (CM) calculation as a compact metric to express the time evolution of spatial patterns in fossil fuel CO2 emissions. The global emission CM has moved toward the east and somewhat south between 1997 and 2010, driven by the increase in emissions in China and South Asia over this time period. Analysis at the level of individual countries reveals a per capita CO2 emission migration in both Russia and India. The per capita emission CM holds potential as a way to succinctly analyze subnational shifts in carbon intensity over time. Uncertainties are generally lower than the previous version of FFDAS due mainly to an improved nightlight data set.
• In November 2014, NASA released an ultra-high-resolution computer model providing a stunning new look at how carbon dioxide in the atmosphere travels around the globe. Plumes of carbon dioxide in the simulation swirl and shift as winds disperse the greenhouse gas away from its sources. The simulation also illustrates differences in carbon dioxide levels in the northern and southern hemispheres and distinct swings in global carbon dioxide concentrations as the growth cycle of plants and trees changes with the seasons. 109) 110)
- The carbon dioxide visualization was produced by a computer model called GEOS-5, created by scientists at NASA Goddard's Global Modeling and Assimilation Office. In particular, the visualization is part of a simulation called a "Nature Run." The Nature Run ingests real data on atmospheric conditions and the emission of greenhouse gases and both natural and man-made particulates. The model is then is left to run on its own and simulate the natural behavior of the Earth's atmosphere. This Nature Run simulates May 2005 to June 2007.
- In the spring of 2014, for the first time in modern history, atmospheric carbon dioxide – the key driver of global warming – exceeded 400 parts per million across most of the northern hemisphere. Prior to the Industrial Revolution, carbon dioxide concentrations were about 270 parts per million. Concentrations of the greenhouse gas in the atmosphere continue to increase, driven primarily by the burning of fossil fuels.
- Despite carbon dioxide's significance, much remains unknown about the pathways it takes from emission source to the atmosphere or carbon reservoirs such as oceans and forests. Combined with satellite observations such as those from NASA's recently launched OCO-2 (Orbiting Carbon Observatory-2), computer models will help scientists better understand the processes that drive carbon dioxide concentrations.
Figure 89: A still image of CO2 concentrations as of January 1, 2006 (image credit: NASA)
Note, the high-resolution visualization of the video representation (Ref. 109) provide a much better impression of the plumes of carbon dioxide as that swirl and shift with the global winds.
TCCON (Total Carbon Column Observing Network):
TCCON is a network of ground-based FTS (Fourier Transform Spectrometers) that record direct solar spectra in the near-infrared. From these spectra, accurate and precise column-averaged abundances of atmospheric constituents including CO2, CH4, N2O, HF, CO, H2O, and HDO, are retrieved. The TCCON is designed to investigate the flow (or flux) of carbon between the atmosphere, land, and ocean (the so-called carbon budget or carbon cycle). This is achieved by measuring the atmospheric mass of carbon (the airborne fraction). The TCCON measurements have improved the scientific community's understanding of the carbon cycle, and urban greenhouse gas emissions. The TCCON supports several satellite instruments by providing an independent measurement to compare (or validate) the satellite measurements of the atmosphere over the TCCON site locations. 111)
This network currently includes over a dozen stations, distributed over a range of latitudes spanning Lauder, New Zealand and Ny Alesund, Norway, and is continuing to grow. To relate TCCON measurements to the WMO CO2 standard, aircraft observations have been collected over several stations, using the same in situ CO2 measurement approaches used to define that standard. OCO-2 will target a TCCON site as often as once each day, acquiring thousands of measurements as it flies overhead. These measurements will be analyzed to reduce biases below 0.1% (0.3 ppm) at these sites. The spaceborne CO2 estimates will be further validated through comparisons with CO2 and surface pressure measurements from ground based sites with the aid of data assimilation models to provide a more complete global assessment of measurement accuracy 112).
In May 2004 a new approach for studying greenhouse gases in our atmosphere came from an unlikely source: a lone trailer in Park Falls, WI, USA. That site became the first station of the TCCON, a ground-based network of instruments providing measurements and data to help better understand the sources and sinks of carbon dioxide (CO2) and methane (CH4) to and from Earth's atmosphere. Now, a decade after the first site became operational, TCCON has expanded and provides important information about regional and global atmospheric levels of carbon-containing gases from many stations, worldwide (Figure 90). 113)
Each of the TCCON stations accommodates a FTS (Fourier Transform Spectrometer) that provides precise measurements of the amount of direct sunlight absorbed by atmospheric gases. At each site, the FTS produces a spectrum of sunlight; from that spectrum, researchers determine the abundance of CO2, CH4, carbon monoxide (CO), and other gases in the atmospheric column extending from the surface of the Earth to the top of the atmosphere. In the absence of clouds, one measurement is made approximately every two minutes.
Data from the individual stations provide information about regional carbon sources and carbon sinks. Furthermore, by combining the data from all the stations, researchers can monitor carbon as it is exchanged—"circulates"—between the atmosphere, the land, and the ocean, explains atmospheric chemist Paul Wennberg at Caltech, who is the elected chair of TCCON.
The TCCON is a partnership arrangement. Although the TCCON stations are scattered around the globe and are overseen by numerous investigators, every partner has agreed on what instruments are used and how they are operated; everyone is using a common analysis software so that the measurements are comparable across the whole network.
Originally, data from each of these stations were intended to help validate measurements obtained from NASA's OCO (Orbiting Carbon Observatory) satellite, which failed upon launch in 2009 due to a faulty fairing separation. OCO and TCCON [were to] provide a new type of data—a type of CO2 measure that had never been used before, called the column average mixing ratio. Measurements from TCCON provide the precise column average mixing ratio of CO2 at discrete locations around the world, and OCO would have provided a similar measurement from space; comparing the two at coincident times and locations were to provide an important evaluation of the satellite data.
Despite the loss of OCO, TCCON continued to expand in recognition of its importance in carbon cycle science and for validation of other remote sensing projects. TCCON provided the very first key observations regarding column average data, long before there were spaceborne estimates.
Table 3: TCCON station locations, lead investigators, and institutions
Figure 90: TCCON has expanded rapidly over the last decade and data have been obtained from 22 locations (red dots) spread around the globe. Blue squares indicate future stations (image credit: Caltech)
Ten Years of Data: Discoveries and Contributions: Over the years, studies using data from TCCON stations have revealed new information about the sources and sinks of CO2 and CH4. These include the discovery of elevated CH4 emissions from Los Angeles, CA, and Four Corners, NM, as well as regional enhancements of CO2 from fossil fuel emissions. Furthermore, TCCON has provided key observations on how uptake of CO2 by the boreal forest—northern forests that span the range from Alaska to Siberia—depends on surface temperature. More broadly, data from TCCON are also being used to evaluate large-scale carbon models and improve global estimates of the sources and sinks of CO2 and CH4 (Figure 91). Understanding the interactions between climate and carbon dynamics is critical for predicting future levels of atmospheric CO2.
The network's ability to collect very precise data has also proved to be very useful for validating the European Space Agency's SCIAMACHY (SCanning Imaging Absorption spectroMeter for Atmospheric CHartographY), which flew on Envisat, launched in 2002, and was the first instrument to yield global measurements of CO2 and CH4 from space. John Burrows, PI of SCIAMACHY remarks, that the creation of TCCON filled a key missing element in the observational system required to meet the challenge [of quantifying] greenhouse gases. In fact, the combination of the SCIAMACHY and TCCON datasets became a milestone in remote sensing, revealing important carbon sources and sinks in Europe, North America, and Siberia. The unprecedented combination of ground-based and spaceborne measurements helped to underscore the importance of wet-land sources of CH4 and the impact of increased CH4 from fracking and oil fields. TCCON has pioneered a key element of the ground segment measurements required to provide the evidence base for policy making for the next 100 years.
More recently, TCCON data have been the core of the validation effort for CO2 and CH4 measurements from the Japanese GOSAT (Greenhouse Gases Observing Satellite) that was launched in January 2009. Osamu Uchino of JAXA says that TCCON has been and will [continue to] be a key [player] in the GOSAT product validation, and together, both TCCON and GOSAT data are contributing significantly to carbon-cycle science.
Figure 91: [Top] Observations of CO2 from TCCON stations have shown that over the past decade, the column mole fraction of CO2 (XCO2) has increased by more than 20 parts per million (ppm). In fact, this past winter (2013-14) all sites in the Northern Hemisphere exceeded 400 ppm. [Bottom] TCCON observations indicate the CH4 concentrations have also increased substantially since 2006–07.
Figure 92: Plots of TCCON data over the period 2004-2013 (image credit: TCCON partners)
Figure 93: TCCON network precision and accuracy (image credit: TCCON partners, Ref. 114)
Table 4: Overview of NASA missions observing/contributing to the global Carbon Cycle measurements and Earth's Changing Climate (NASA missions) 116)
Land Cover Change:
Background: The physical surface of the Earth is in constant change: abundant water resources give rise to new growth, cities expand, what was once forest is converted to farmland. Man causes some of these transformations; others are merely the result of the changing of the seasons. Most fundamentally, land cover is a way of portraying the surface of the Earth. Often this is done through a process of classification where regions of the Earth are identified according to some of their more prominent,quantifiable attributes. Researchers are frequently interested in how land cover changes in a given area through time.
The pace, magnitude and spatial reach of human alterations of the Earth's land surface are unprecedented. Land use and land cover change directly impacts biotic diversity worldwide, contributes to climate change, is the primary source of soil degradation, and, by altering ecosystem services, affects the ability of biological systems to support human needs. Such changes also determine, in part, the vulnerability of places and people to climatic, economic or socio-political perturbations. LUCC (Land Use and Cover Change) research, a program of IGBP, addresses the problem of land use dynamics through comparative case study analysis, addresses land cover dynamics through empirical observations and diagnostic models, and extends the understanding of cause-use-cover dynamics through integrated regional and global modeling. 117)
The LUCC objectives are:
• To develop a fundamental understanding of the human and biophysical dynamics of land-use changes ad the impacts of these changes on land cover.
• To develop robust and regionally sensitive global models of land-use/cover change with improved capacities to predict and project use/cover changes.
• To develop an understanding of land-use/cover dynamics through systematic and integrated case studies.
• To assist in the development of a global land-use classification scheme LUCC was completed in 2005.
The use of satellite imagery has made the mapping of land cover much more practical. Currently, it is possible to look at land cover from global to local scales. This type of analysis has proven helpful to a variety of disciplines, from archeology to forestry to hydrology.
The global land cover map of Figure 94 was created using data from ESA's Envisat mission for the 2010 epoch (2008–12). This is the most recent data product from the CCI (Climate Change Initiative) Land Cover team led by the Catholic University of Leuven, Belgium, showing 22 different types of global land cover classes, plus 14 regional land cover classes. 118)
Following the GCOS (Global Climate Observing System) Implementation Plan, the purpose of the CCI Land Cover project is to make the best use of available satellite sensor data to provide an accurate land-cover classification that can serve the climate modelling community. The maps propose a legend based on the FAO/UNEP Land Cover Classification System, in order to be compatible with previous products.
The land-cover maps are currently under validation by regional experts, coordinated by the European Commission's JSC (Joint Research Centre).
Figure 94: Global land cover 2010 - the latest land-cover map for studying the effects of climate change, conserving biodiversity and managing natural resources (image credit: ESA, CCI Land Cover, Catholic University of Leuven)
Naturally, there are also many land cover change maps on a regional basis. An example is the "Land Cover Change in the Eastern United States," provided by the USGS (United States Geological Survey). As part of a national assessment of U.S. land change, the USGS recently completed an analysis of 20 Eastern U.S. eco-regions (Figure 95). The 20 eco-regions spanan area of 1,650,930 km2, as defined by the EPA (Environmental Protection Agency). 119)
Figure 95: Land cover of the 20 Eastern U.S. eco-regions comprising the "forested east" (image credit: USGS)
Ozone layer on the road to recovery in 2014 (UNEP/WMO)
• September 2014: Earth's protective ozone layer is on track for recovery within the next few decades according to a new assessment by 282 scientists from 36 countries. The abundance of most ozone-depleting substances in the atmosphere has dropped since the last assessment in 2010, and stratospheric ozone depletion has leveled off and is showing some signs of recovery. These observations were the headlines of the recent "Assessment for Decision-Makers," part of a larger report to be released in early 2015 by UNEP (United Nations Environment Program) and WMO (World Meteorological Organization). 120) 121) 122) 123)
The stratospheric ozone layer shields us from most of the damaging ultraviolet rays from the Sun. In 1974, scientists discovered that chlorine- and bromine-containing compounds such as chlorofluorocarbons (CFCs) and halons could deplete the ozone layer, and by the mid-1980s, they had observational evidence that it was happening. In 1987, international leaders crafted a treaty to phase out the production and consumption of these ozone-depleting chemicals. The Montreal Protocol was signed on September 16, 1987, and the date is celebrated each year as the International Day for the Preservation of the Ozone Layer.
Stratospheric ozone is typically measured in DU (Dobson Units), the number of molecules required to create a layer of pure ozone 0.01 mm thick at a temperature of 0º Celsius and an air pressure of 1 atmosphere (the pressure at the surface of the Earth). The average amount of ozone in Earth's atmosphere is 300 Dobson Units, equivalent to a layer with the height of 2 pennies stacked together.
According to the UNEP/WMO assessment, total column ozone declined about 2.5% over most of the world during the 1980s and early 1990s, but has remained relatively unchanged since 2000. The amount of ozone-destroying chlorine and bromine compounds in the air has dropped by 10 to 15 % since a peak in the late 1990s. And by some accounts, ozone levels in the upper stratosphere may now be increasing slightly.
However, the road to recovery will be a long one. Ozone-depleting chemicals—which were once used for refrigerants, aerosol spray cans, insulation foam, and fire suppression—persist for decades in the atmosphere. Though CFCs and similar chemicals were phased out years ago, the existing gases in the stratosphere will take many years to decay. If nations continue to follow the guidelines of the Montreal Protocol, the UNEP/WMO report notes, ozone levels over most of the globe should recover to 1980 levels by 2050. The ozone hole over the South Pole will take longer to recover, ending by 2070.
Beyond the positive impact on the ozone layer, the banning of CFCs and similar compounds has had a positive effect on climate because such chemicals are also greenhouse gases. The UNEP/WMO team cautioned that one of the key replacements for CFCs—hydrofluorocarbons (HFCs)—do not harm the ozone layer but they are potent greenhouse gases that could contribute substantially to climate change in the coming decades.
Figure 96: Antarctic ozone hole (false color view) on September 12, 2014, as observed by the OMI (Ozone Monitoring Instrument) on the Aura satellite (image credit: NASA Earth Observatory)
GMSLR (Global Mean Sea Level Rise)
The IPCC (Intergovernmental Panel on Climate Change), set up by WMO and UNEP in 1988, is an international panel to advise policy makers. The IPCC organizes a number of meetings with different objectives and level of participation. They include Plenary sessions of the IPCC and IPCC Working Groups which are attended by representatives from governments and participating organizations, sessions of the IPCC Bureau, the Task Force Bureau and any task group set up by the Panel, as well as workshops, scoping and other expert meetings, and meetings of lead authors involved in preparing an IPCC report. The IPCC co-sponsors also meetings to support the assessment process, to disseminate its results and enhance interaction with scientists and users. Official documents of past and upcoming sessions of the IPCC and IPCC Working Groups, and approved reports of sessions of the IPCC and the IPCC Bureau can be found at the following reference. 124) (currently documents since 2001).
The Fourth Assessment Report of the IPCC in 2007 is intended to assess the scientific, technical and socio-economic information concerning climate change, its potential effects, and options for adaptation and mitigation. The report is the largest and most detailed summary of the climate change situation ever undertaken, produced by thousands of authors, editors, and reviewers from dozens of countries, citing over 6,000 peer-reviewed scientific studies. 125)
Some background: The ocean has an important role in climate variability and change. The ocean's heat capacity is about 1,000 times larger than that of the atmosphere, and the oceans net heat uptake since 1960 is around 20 times greater than that of the atmosphere. This large amount of heat, which has been mainly stored in the upper layers of the ocean, plays a crucial role in climate change, in particular variations on seasonal to decadal time scales. The transport of heat and freshwater by ocean currents can have an important effect on regional climates, and the large-scale MOC (Meridional Overturning Circulation); also referred to as thermohaline circulation) influences the climate on a global scale. 126)
Life in the sea is dependent on the biogeochemical status of the ocean and is influenced by changes in the physical state and circulation. Changes in ocean biogeochemistry can directly feed back to the climate system, for example, through changes in the uptake or release of radiatively active gases such as carbon dioxide. Changes in sea level are also important for human society, and are linked to changes in ocean circulation. Finally, oceanic parameters can be useful for detecting climate change, in particular temperature and salinity changes in the deeper layers and in different regions where the short-term variability is smaller and the signal-to-noise ratio is higher.
The large-scale, three-dimensional ocean circulation and the formation of water masses that ventilate the main thermocline together create pathways for the transport of heat, freshwater and dissolved gases such as carbon dioxide from the surface ocean into the density-stratified deeper ocean, thereby isolating them from further interaction with the atmosphere. These pathways are also important for the transport of anomalies in these parameters caused by changes in the surface conditions. Furthermore, changes in the storage of heat and in the distribution
Changes in Sea Level: Present-day sea level change is of considerable interest because of its potential impact on human populations living in coastal regions and on islands. The focus is on global and regional sea level variations, over time spans ranging from the last decade to the past century.
Processes in several nonlinearly coupled components of the Earth system contribute to sea level change, and understanding these processes is therefore a highly interdisciplinary endeavor. On decadal and longer time scales, global mean sea level change results from two major processes, mostly related to recent climate change, that alter the volume of water in the global ocean: i) thermal expansion, and ii) the exchange of water between oceans and other reservoirs (glaciers and ice caps, ice sheets, other land water reservoirs - including through anthropogenic change in land hydrology, and the atmosphere.
All these processes cause geographically nonuniform sea level change as well as changes in the global mean; some oceanographic factors (e.g., changes in ocean circulation or atmospheric pressure) also affect sea level at the regional scale, while contributing negligibly to changes in the global mean. Vertical land movements such as resulting from GIA (Glacial Isostatic Adjustment), tectonics, subsidence and sedimentation influence local sea level measurements but do not alter ocean water volume; nonetheless, they affect global mean sea level through their alteration of the shape and hence, the volume of the ocean basins containing the water.
Measurements of present-day sea level change rely on two different techniques: tide gages and satellite altimetry.
• Tide gages provide sea level variations with respect to the land on which they lie. To extract the signal of sea level change due to ocean water volume and other oceanographic change, land motions need to be removed from the tide Gage measurement. Land motions related to GIA can be simulated in global geodynamic models. The estimation of other land motions is not generally possible unless there are adequate nearby geodetic or geological data, which is usually not the case. However, careful selection of tide gage sites such that records reflecting major tectonic activity are rejected, and averaging over all selected gages, results in a small uncertainty for global sea level estimates.
• Sea level change based on satellite altimetry is measured with respect to the Earth's center of mass, and thus is not distorted by land motions, except for a small component due to large-scale deformation of ocean basins from GIA.
The global sea level rose by about 120 m during the several millennia that followed the end of the last ice age (approximately 21,000 years ago), and stabilized between 3,000 and 2,000 years ago. Sea level indicators suggest that global sea level did not change significantly from then until the late 19th century. The instrumental record of modern sea level change shows evidence for onset of sea level rise during the 19th century. Estimates for the 20th century show that global average sea level rose at a rate of about 1.7 mm/year.
Satellite observations available since the early 1990s provide more accurate sea level data with nearly global coverage. This decade-long satellite altimetry data set shows that since 1993, the sea level has been rising at a rate of around 3 mm/year, significantly higher than the average during the previous half century. Coastal tide gage measurements confirm this observation, and indicate that similar rates have occurred in some earlier decades.
In agreement with climate models, satellite data and hydrographic observations show that sea level is not rising uniformly around the world. In some regions, rates are up to several times the global mean rise, while in other regions sea level is falling. Substantial spatial variation in rates of sea level change is also inferred from hydrographic observations. Spatial variability of the rates of sea level rise is mostly due to non-uniform changes in temperature and salinity and related to changes in the ocean circulation.
Near-global ocean temperature data sets made available in recent years allow a direct calculation of thermal expansion. It is believed that on average, over the period from 1961 to 2003, thermal expansion contributed about 1/4 of the observed sea level rise, while melting of land ice accounted for less than half. Thus, the full magnitude of the observed sea level rise during that period was not satisfactorily explained by those data sets, as reported in the IPCC Third Assessment Report.
Global sea level is projected to rise during the 21st century at a greater rate than during 1961 to 2003. Under the IPCC Special Report on Emission Scenarios (SRES) A1B scenario by the mid-2090s 127), for instance, global sea level reaches 0.22 to 0.44 m above the 1990 levels, and is rising at about 4 mm/year. As in the past, sea level change in the future will not be geographically uniform, with regional sea level change varying within about ±0.15 m of the mean in a typical model projection. Thermal expansion is projected to contribute more than half of the average rise, but land ice will lose mass increasingly rapidly as the century progresses. An important uncertainty relates to whether discharge of ice from the ice sheets will continue to increase as a consequence of accelerated ice flow, as has been observed in recent years. This would add to the amount of sea level rise, but quantitative projections of how much it would add cannot be made with confidence, owing to limited understanding of the relevant processes.
Figure 97: The evolution of global mean sea level in the past and as projected for the 21st century for the SRES A1B scenario (image credit: IPCC)
Legend to Figure 97: Time series of global mean sea level (deviation from the 1980-1999 mean) in the past and as projected for the future. For the period before 1870, global measurements of sea level are not available. The grey shading shows the uncertainty in the estimated long-term rate of sea level change. - The red line is a reconstruction of global mean sea level from tide gages, and the red shading denotes the range of variations from a smooth curve. - The green line shows global mean sea level observed from satellite altimetry. - The blue shading represents the range of model projections for the SRES A1B scenario for the 21st century, relative to the 1980 to 1999 mean, and has been calculated independently from the observations.
According to NOAA (National Oceanic and Atmospheric Administration), Washington, D.C., the current sea level rise is about 3 mm/year worldwide. This is a significantly larger rate than the sea-level rise averaged over the last several thousand years, and the rate may be increasing. Sea level rises can considerably influence human populations in coastal and island regions and natural environments like marine ecosystems. 128)
Figure 98: Long-term global sea level rise observations of altimetric missions (image credit: NOAA)
Legend to Figure 98: The data record built by the missions T/P, Jason-1, GFO, ERS-1 & -2, Envisat, and Jason-2 represents the first multi-decadal global record for addressing the issue of sea level rise - which has been identified by the 2007 IPCC (Inter-Governmental Panel for Climate Change) assessment as one of the most important consequences and indicators of global climate change.
Between 1870 and 2004, global average sea levels rose a total of 195 mm which is about 1.46 mm/year. From 1950 to 2009, measurements show an average annual rise in sea level of 1.7 ± 0.3 mm/year, with satellite data showing a rise of 3.3 ± 0.4 mm/year from 1993 to 2009.
The global mean sea level rise is caused by an increase in the volume of the global ocean. This in turn is caused by:
• Warming the ocean (thermal expansion)
• Loss of ice by glaciers and ice sheets
• Reduction of liquid water storage on land.
Sea level rise is one of several lines of evidence that support the view that the global climate has recently warmed. The global community of climate scientists confirms that it is very likely human-induced (anthropogenic) warming contributed to the sea level rise observed in the latter half of the 20th century.
Changes in the ocean and on land, including observed decreases in snow cover and Northern Hemisphere sea ice extent, thinner sea ice, shorter freezing seasons of lake and river ice, glacier melt, decreases in permafrost extent, increases in soil temperatures and borehole temperature profiles, and sea level rise, provide additional evidence that the world is warming.
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The information compiled and edited in this article was provided by Herbert J. Kramer from his documentation of: "Observation of the Earth and Its Environment: Survey of Missions and Sensors" (Springer Verlag) as well as many other sources after the publication of the 4th edition in 2002. - Comments and corrections to this article are always welcome for further updates (firstname.lastname@example.org).