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ESA-CCI (European Space Agency-Climate Change Initiative)

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• October 19, 2021: While the climate crisis is, unfortunately, a reality, it is all too easy to assume that every aspect of our changing world is a consequence of climate change. Assumptions play no role in key environmental assessments and mitigation strategies such as we will see in the upcoming UN climate change COP-26 conference – it’s the science and hard facts that are critical. New research published this week is a prime example of facts that matter. Using model projections combined with satellite data from ESA’s Climate Change Initiative, this latest research shows that the global rise in the temperature of lake water and dwindling lake-ice cover can only be explained by the increase in greenhouse gas emissions since the industrial revolution – in other words, humans are clearly to blame. 1)

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Figure 1: Lake Ontario temperature. According to a paper published in Nature Geoscience, the influence of human-induced climate change is evident in the fact that lake-water temperatures are rising in the fact that lake ice-cover forms later and melts sooner. At the beginning of the project, the authors observed changes in lakes around the world based on satellite-derived observations from ESA’s Climate Change Initiative lakes project – as depicted in this image of Lake Ontario from 31 August 2019 (image credit: ESA/CCI Lakes project, CC BY-SA 3.0 IGO)

- Luke Grant, from the Vrije Universiteit Brussel (VUB) and lead author, said, “These physical properties are fundamental to lake ecosystems. As impacts continue to increase in the future, we risk severely damaging lake ecosystems, including water quality and populations of native fish species. This would be disastrous for the many ways in which local communities depend on lakes, such as drinking water supply and fishing.” 2)

- The research team also predicted how things are likely to develop in the future under different warming scenarios.

- The graph of Figure 2 shows that in a low-emission scenario, the average warming of lakes is estimated to stabilize at 1.5°C above pre-industrial levels and the duration of ice cover to be 14 days shorter. In a high-emission world, these changes could lead lake temperature to increase by 4.0 °C and have 46 fewer days of ice per year.

- At the beginning of the project, the authors observed changes in lakes around the world, as depicted in the image of Lake Ontario, based on satellite-derived observations from ESA’s Climate Change Initiative lakes project.

- However, the role of climate change in these trends had not yet been demonstrated.

- “In other words, we had to rule out the possibility that these changes were caused by the natural variability of the climate system,” says fellow VUB researcher and study co-author Inne Vanderkelen.

- The team therefore developed multiple computer simulations with models of lakes on a global scale, on which they then ran a series of climate models. Once the team had built up this database, they applied a methodology described by the Intergovernmental Panel on Climate Change. After determining the historical impact of climate change on lakes, they also analyzed various future climate scenarios.

- The results show that it is highly unlikely that the trends in lake temperatures and ice cover in recent decades can be explained solely by natural climate variability.

- Moreover, the researchers found clear similarities between the observed changes in lakes and model simulations of lakes in a climate influenced by greenhouse gas emissions.

- “This is clear evidence that human-induced climate change has an impact on lakes,” says Iestyn Woolway, former ESA Fellow and co-author of the study.

- Projections of lake temperatures and ice cover unanimously indicate increasing trends for the future.

- For every 1°C increase in global air temperature, lakes are estimated to warm by 0.9°C and lose 9.7 days of ice cover. In addition, the analysis revealed significant differences in the impact on lakes at the end of the century, depending on the measures we take to combat climate change.

- “Our results underline the great importance of the Paris Agreement to protect the health of lakes around the world,” said Wim Thiery, VUB climate expert and senior author of the study. “If we manage to drastically reduce our emissions in the coming decades, we can still avoid the worst consequences for lakes worldwide.”

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Figure 2: Projection of future lake surface-water temperature. Historic and future projections of globally averaged lake surface-water temperature anomalies (relative to the global temporal average of the pre-industrial control simulation). The temporal changes in lake-surface temperature anomalies are shown from 1900 to 2100 under historic (1900–2005) and future (2006 –2100) climate forcing (Representative Concentration Pathway [RCP] 2.6, 6.0, 8.5). For comparison the model projections are also shown from 1900 to 2100 for the pre-industrial climate, where the influence of anthropogenic greenhouse gases is omitted. For simplicity, the uncertainties for each dataset are not shown. [map credit: Re-drawn from Grant et al. (2021)]

• August 5, 2021: Forests are not only key to moderating our climate by sequestering atmospheric carbon, but they also create a cooling effect by increasing low-level cloud. A first global assessment using satellite observations has shown that for two-thirds of the world, afforestation increases low-level cloud cover, with the effect being strongest over evergreen needleleaf forest. 3)

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Figure 3: A first global assessment using satellite observations shows that for two-thirds of the world, afforestation increases low-level cloud cover, with the effect being strongest over evergreen needleleaf forest. Because trees sequester carbon dioxide from the atmosphere and convert it into biomass, forests are widely championed for their role in mitigating climate change. However, forests also offer climate benefits through localized cooling by increasing cloud cover and generating rainfall (image credit: Pixabay/jpleno)

Because trees sequester carbon dioxide from the atmosphere and convert it into biomass, forests are widely championed for their role in mitigating climate change. What has been less clear, however, is how forests affect the climate in other ways such as their role in the water cycle and surface energy balance.

The paper, published recently in Nature Communications, uses global data records of cloud and land-fractional cover produced by ESA’s Climate Change Initiative to examine the effect of the transition of vegetation cover into deciduous and evergreen forest. 4)

“Earth observations are increasingly showing that trees and forests are impacting climate by affecting biophysical surface properties,” says one of the co-authors of the study, Alessandro Cescatti.

The paper describes how cloud generally increased over the whole year in afforested areas in temperate, tropical and arid regions, sometimes by as much as 15%.

However, during the boreal winter and spring across North America, Russia and Eastern Europe, when these regions have prolonged snow cover, the authors found a reduction in cloud cover over forests compared to open land. The boreal summer, on the other hand, has strong and consistent increases in cloud fraction by about 5%.

“Without global cloud and land-cover type observations from satellites this study would not have been possible on a global scale,” says Martin Stengel, who was not involved in the study but leads the Climate Change Initiative Cloud project. “The authors of this study appreciated the high-spatial resolution of the initiative’s products.”

Dr Cescatti added, “Studies like this one, based on robust satellite observations, are fundamental to characterize the complexity of the climate system and provide benchmarks for climate model developments.”

The team emphasizes that land-based climate mitigation through afforestation, forest restoration and avoided deforestation should not be reasoned purely in terms of carbon capture. Instead, policies should include the wider climate benefits that forests offer, including increasing cloud cover for localized cooling and generating rainfall, giving forests additional hydrological value.

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Figure 4: The effect of afforestation on fractional cloud cover for different forest types. A first global assessment using satellite observations shows that for two-thirds of the world, afforestation increases low-level cloud cover, with the effect being strongest over evergreen needleleaf forest (image credit: ESA)

• Earth observation satellites carry a wide variety of instruments using both passive and active sensing techniques. These sensors detect radiation in different parts of the electromagnetic spectrum, depending on the sensor type. 5)

The ESA Climate Change Initiative is unique in merging data from different sensors, on missions flown by different space agencies, to generate climate data records with the longest possible time spans. Here are some of the major ESA missions used to construct long-term records of Essential Climate Variables.

ERS | ENVISAT | CryoSat | SMOS | Sentinel-1 | Sentinel-2 | Sentinel-3 | Sentinel-5P | Future missions for climate (EarthCARE, Biomass, FLEX, FORUM).

• The United Nations Framework Convention on Climate Change leads international efforts to combat climate change and limit global temperature rise to less 2°C above what it was in pre-industrial times, as set out in the Paris Agreement. Robust scientific evidence of change is fundamental this challenging task. 6)

Through its Climate Change Initiative (CCI), ESA develops a suite of satellite data records of key components of the climate system, known as Essential Climate Variables (ECVs). Scientists use ECVs to study climate drivers, interactions and feedbacks, as well as reservoirs, tipping points and fluxes of energy, water, and carbon. These climate-quality datasets are a major contribution to the evidence base used to understand climate change and to predict the future, which drives international action.



1) ”Humans to blame for warming lakes,” ESA Applications, 19 October 2021, URL: https://www.esa.int/Applications/Observing_the_Earth
/Space_for_our_climate/Humans_to_blame_for_warming_lakes

2) Luke Grant, Inne Vanderkelen, Lukas Gudmundsson, Zeli Tan, Marjorie Perroud, Victor M. Stepanenko, Andrey V. Debolskiy, Bram Droppers, Annette B. G. Janssen, R. Iestyn Woolway, Margarita Choulga, Gianpaolo Balsamo, Georgiy Kirillin, Jacob Schewe, Fang Zhao, Iliusi Vega del Valle, Malgorzata Golub, Don Pierson, Rafael Marcé, Sonia I. Seneviratne & Wim Thiery, ”Attribution of global lake systems change to anthropogenic forcing,” Nature Geoscience, Published: 18 October 2021, https://doi.org
/10.1038/s41561-021-00833-x

3) ”Satellites reveal how forests increase cloud and cool climate,” ESA Applications, 5 August 2021, URL: https://www.esa.int/Applications/Observing_the_Earth/
Space_for_our_climate/Satellites_reveal_how_forests_increase_cloud_and_cool_climate

4) Gregory Duveiller, Federico Filipponi, Andrej Ceglar, JÄ™drzej Bojanowski, Ramdane Alkama & Alessandro Cescatti, ”Revealing the widespread potential of forests to increase low level cloud cover,” Nature Communications, Volume 12, Article Nr. 4337, Published: 15 July 2021, https://doi.org
/10.1038/s41467-021-24551-5
, URL: https://www.nature.com/articles/s41467-021-24551-5.pdf

5) ”ESA Missions for Climate,” ESA, URL: https://climate.esa.int/en/evidence/esa-missions-relating-climate/

6) ”ESA’s Climate Change Initiative,” ESA Applications, URL: https://www.esa.int/Applications/
Observing_the_Earth/Space_for_our_climate/ESA_s_Climate_Change_Initiative
....


The information compiled and edited in this article was provided by Herbert J. Kramer from his documentation of: ”Observation of the Earth and Its Environment: Survey of Missions and Sensors” (Springer Verlag) as well as many other sources after the publication of the 4th edition in 2002. - Comments and corrections to this article are always welcome for further updates (herb.kramer@gmx.net).

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