EO (Earth Observation) Topics on Climate Change
EO (Earth Observation) Topics on Climate Change
Sea Ice Record Lows 2016 - Warmest year Changing rainfall patterns Ozone Hole 2016
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.
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. 4) 5) 6)
Figure 1: 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 2: 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 3: 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 4: 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. 7)
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 5: 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 6: 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. 8) 9)
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 7: 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. 10)
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 8 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 9 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.
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. 11)
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. 12)
"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 10) 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 10: 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. 13)
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 11). 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. 14)
Figure 11: 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 12), 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 12a,b).
Figure 12: 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. 15) 16)
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 13. 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 13). There are several theories to explain this variability, but here we present an additional explanation, with important implications for anticipated near-future acceleration.
Legend to Figure 13: 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 14. 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.
Legend to Figure 14: 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 15 and 16). 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 16).
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.
Legend to Figure 15: 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 16: 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 16: 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. 17)
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. 18)
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. 19) 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? 20)
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 17: 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. 21)
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. 22)
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 18 and 19 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.
Legend to Figure 18: Each colored circle represents a colonies' current population trend. The black dashed line separates West Antarctic Peninsula (WAP) from continental Adélie penguin colonies.
Figure 19: 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. 23)
- 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 20 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 20: 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. 24)
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. 25) 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 21: 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 22: 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)
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. 26)
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. 27) The atmospheric data products are available through the GHG-CCI website.28)
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 23: 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 24: 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. 29) 30)
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 25: 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. 31) 32)
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 26) 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. 32).
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.
Legend to Figure 26: (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; http://odv.awi.de/en/data/ ocean/world_ocean_atlas_2013/). (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 27) 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 27).
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 28a). 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 28a). 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.
Legend to Figure 27: (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 28 a,b are indicated.
Legend to Figure 28: (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 28 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 28 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 28 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 28 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 29).
Legend to Figure 29: (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 26). PIP25 values are used to identify low (0–20%), common (20–50%), ice-edge (50–70%) and extended (>70%) sea-ice concentrations (see Figure 26). 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 29). 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 26). 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 29) 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 29). 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 26 and 30). 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 30).
Legend to Figure 30: 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 26). 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. 33)
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 31 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 31: 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.
Legend to Figure 32: 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 33, 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.
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: 34)
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 34: 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. 35) 36) 37)
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.
Legend to Figure 35: 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 36: Storage trends partitioned into hydrologic gains and losses. Left: As in Figure 35, 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 37: 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. 38) 39) 40) 41) 42) 43)
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. 44) 45)
Figure 38: 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 39: 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. 46)
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. 47)
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 40: 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 41: 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 42: 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. 48)
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 43, 45, 46 and 47), 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 48 and 50), 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. 49)
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 43: 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 45: 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 49: Color bar for the trend in nitrogen dioxide concentrations changes across the United Sates
Figure 51: 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. 50) 51) 52)
- 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 52: 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 52: 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 52 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.