Category Archives: Nature

How Will the Biggest Tropical Trees Respond to Climate Change? (Botany / Nature)

Giant trees in tropical forests, witnesses to centuries of civilization, may be trapped in a dangerous feedback loop according to a new report in Nature Plants from researchers at the Smithsonian Tropical Research Institute (STRI) in Panama and the University of Birmingham, U.K. The biggest trees store half of the carbon in mature tropical forests, but they could be at risk of death as a result of climate change—releasing massive amounts of carbon back into the atmosphere.

Evan Gora, STRI Tupper postdoctoral fellow, studies the role of lightning in tropical forests. Adriane Esquivel-Muelbert, lecturer at the University of Birmingham, studies the effects of climate change in the Amazon. The two teamed up to find out what kills big tropical trees. But as they sleuthed through hundreds of papers, they discovered that nearly nothing is known about the biggest trees and how they die because they are extremely rare in field surveys.

“Big trees are hard to measure,” said Esquivel-Muelbert. “They are the pain in a field campaign because we always have to go back with a ladder to climb up to find a place to measure the circumference above the buttresses. It takes a long time. Studies focusing on the reasons trees die don’t have enough information for the biggest trees and often end up excluding them from their analysis.”

 “Because we generally lack the data necessary to tell us what kills trees that are above approximately 50 centimeters in diameter, that leaves out half of the forest biomass in most forests,” Gora said.

Only about 1% of trees in mature tropical forests make it to this size. Others wait their turn in the shade below.

The other thing that makes tropical forests so special—high biodiversity—also makes it difficult to study big trees: There are so many different species, and many of them are extremely rare.

“Because only 1–2% of big trees in a forest die every year, researchers need to sample hundreds of individuals of a given species to understand why they are dying,” Gora said. “That may involve looking for trees across a huge area.”

Imagine a study of blood pressure in people who have lived to be 103. One would have to locate and test seniors from cities and towns around the world: a time-consuming, logistically complex and expensive proposition.

A large body of evidence shows that trees are dying faster in tropical forests than ever before. This is affecting the ability of forests to function and in particular, to capture and store carbon dioxide.

“We know the deaths of largest and oldest trees are more consequential than the death of smaller trees,” Gora said. “Big trees may be at particular risk because the factors that kill them appear to be increasing more rapidly than the factors that seem to be important for smaller-tree mortality.”

In large parts of the tropics, climate change is resulting in more severe storms and more frequent and intense droughts. Because big trees tower above the rest, they may be more likely to be hit by lightning, or damaged by wind. Because they have to pull ground water higher than other trees, they are most likely to be affected by drought.

Hoping to better understand what is happening to big trees, Gora and Esquivel-Muelbert identified three glaring knowledge gaps. First, almost nothing is known about disease, insects and other biological causes of death in big trees. Second, because big trees are often left out of analyses, the relationship between cause of death and size is not clear. And, finally, almost all of the detailed studies of big tropical trees are from a few locations like Manaus in Brazil and Barro Colorado Island in Panama.

To understand how big trees die, there is a trade-off between putting effort into measuring large numbers of trees and measuring them often enough to identify the cause of death. Gora and Esquivel-Muelbert agree that a combination of drone technology and satellite views of the forest will help to find out how these big trees die, but this approach will only work if it is combined with intense, standardized, on-the-ground observations, such as those used by the Smithsonian’s international ForestGEO network of study sites.

Esquivel-Muelbert hopes that the impetus for this research will come from a shared appreciation for these mysterious living monuments:

“I think they are fascinating to everyone,” she said. “When you see one of those giants in the forest, they are so big. My colleague and Amazonian researcher, Carolina Levis, says that they are the monuments we have in the Amazon where we don’t have big pyramids or old buildings.…That is the feeling, that they have been through so much. They are fascinating, not just in the scientific sense but also in another way. It moves you somehow.”

Funding for this study was from STRI, the U.S. National Science Foundation and the TreeMort project as part of the EU Framework Programme for Research and Innovation.

The Smithsonian Tropical Research Institute, headquartered in Panama City, Panama, is a unit of the Smithsonian Institution. The institute furthers the understanding of tropical biodiversity and its importance to human welfare, trains students to conduct research in the tropics and promotes conservation by increasing public awareness of the beauty and importance of tropical ecosystems. Promo video.

Featured image: Tropical trees may grow to be more than 250 feet (77 meters) tall. Note person in red on the forest floor, below. Credit: Evan Gora, STRI

Reference: Gora, E.M. and Esquivel-Muelbert, A. 2021. Implications of size-dependent tree mortality for tropical forest carbon dynamics. Nature Plants. doi: 10.1038/s41477-021-00879-0

Provided by Smithsonian

How Bushfire Smoke Traveled Around the World? (Nature)

A study uncovers how some Australian fires produced a spreading stratospheric haze rivaling that of a volcanic eruption

It’s not just how hot the fires burn – it’s also where they burn that matters. During the recent extreme fire season in Australia, which began in 2019 and burned into 2020, millions of tons of smoke particles were released into the atmosphere. Most of those particles followed a typical pattern, settling to the ground after a day or week; yet the ones created in fires burning in one corner of the country managed to blanket the entire Southern hemisphere for months. A pair of Israeli scientists managed to track puzzling January and February 2020 spikes in a measure of particle-laden haze to those fires, and then, in a paper recently published in Science, they uncovered the “perfect storm” of circumstances that swept the particles emitted from those fires into the upper atmosphere and spread them over the entire Southern Hemisphere.

Particles reaching the stratosphere – the upper layer of the atmosphere – most often get there through volcanic eruptions. The ash emitted in the more extreme eruptions dims the sun and cools the planet, as well as producing spectacular sunsets. Prof. Ilan Koren of the Weizmann Institute of Science’s Earth and Planetary Science Department, who conducted the study together with his former student, Dr. Eitan Hirsch, now the Head of the Environmental Sciences Division at the Israel Institute for Biological Research in Ness Tziona, had noticed an extreme increase in a satellite-based measure of particle loading in the atmosphere called AOD – or aerosol optical depth. In January 2020, those measurements, plotted in standard deviations, showed a deviation three times the normal – some of the highest readings ever obtained, higher even than those from Mt. Pinatubo in 1991. But the timing did not coincide with any volcanic activity. They wondered if fires might be to blame, even though it is rare for the smoke from fires to escape the lower layer of atmosphere known as the troposphere in significant amounts. The troposphere extends from the ground to a height of several kilometers, and if smoke particles manage to rise that high, they hit an inversion layer called the tropopause that acts as a sort of ceiling between the troposphere and the stratosphere.

Up in the stratosphere, the particles found themselves in a different world than the one they had just left

Working backwards and using data from several satellites, including, in addition to AOD, LIDAR readings that revealed how the particles were distributed vertically in “slices” of atmosphere, the two were able to prove that the source of the spikes was bushfires – specifically those burning in Southeastern Australia. Further analysis of satellite data revealed the broad band of haze in the stratosphere spreading to cover the Southern hemisphere, peaking from January to March and persisting through July; reaching all the way around and back to Australia’s west coast.

How did these smoke particles penetrate through the tropopause ceiling and why did they come from these fires and not the others? One clue, says Hirsch, lay in another, distant forest fire that had occurred several years ago in Canada. Then, too, high AOD levels had been recorded. Both of these fires occurred in high latitudes, away from the equator.

The height of the troposphere shrinks at these latitudes: Over the tropics its upper ceiling can reach up to 18 km above the surface, while somewhere above the 45th parallel – North and South, it takes a sudden step down to around 8-10 km in height. So the first element enabling the particles’ trans-layer flight was simply having less atmosphere to cross.

Video: Images from Suomi National Polar-orbiting Partnership show Australian bushfire smoke heading east. Images show half the Pacific Ocean

Pyrocumulus clouds – clouds fueled by the fires’ energy – were considered as a means of transporting smoke to the stratosphere. However, when inspecting the satellite data, Hirsch and Koren noticed that pyrocumulus clouds formed only over a small fraction of the fires’ duration, and they were mostly seen over fires burning on the central part of the coast. In other words, these clouds could not explain the large amounts found to be transported to the stratosphere, and an additional mechanism for lifting smoke downwind from the sources was missing.   

This brings up the second element: the weather patterns in the strip known as the mid-latitude cyclone belt that runs through the southern end of Australia, one of the stormiest regions on the planet. The smoke was first advected (moved horizontally) by the prevailing winds in the lower atmosphere to the Pacific Ocean, and then some of it converged into the deep convective clouds there and was lifted in the clouds’ core into the stratosphere. An interesting feedback mechanism known as “cloud invigoration by aerosols” can further deepen the clouds. In a previous study, the authors had shown that in conditions such as the pristine environment over the Southern Ocean, the convective clouds are “aerosol limited.” The elevated smoke levels could thus act as cloud condensation nuclei, allowing the clouds to develop deeper and thus increasing the number of clouds that able to penetrate the tropopause and inject the smoke in the stratosphere.

Up in the stratosphere, the particles found themselves in a different world than the one they had just left. If below they were at the mercy of mixing and churning air currents, up on top the air moves in a steady, linear fashion. That is, there was one strong current, and it was moving them eastwards over the ocean to South America and back over the Indian Ocean toward Australia, and slowly settling around the entire hemisphere. “People in Chile were breathing particles from the Australian fires,” says Hirsch. By sailing on an endless air current, these particles remained airborne for much longer than lower atmosphere smoke particles.

“For people on the ground, the air may have just seemed a bit hazier or the sunsets a bit redder. But such a high AOD – much, much higher than normal – means sunlight was getting blocked, just as it does after volcanic eruptions,” says Koren. “So the ultimate effect of that smoke on the atmosphere was cooling, though we still do not know how much influence that cooling and dimming may have had on the marine environment or weather patterns.

“There are always fires burning in California, in Australia and in the tropics,” he adds. “We might not be able to stop all of the burning, but we do need an understanding that the precise locations of those fires may grant them very different effects on our atmosphere.”

Prof. Ilan Koren’s research is supported by the de Botton Center for Marine Science; the Sussman Family Center for the Study of Environmental Sciences; the Dr. Scholl Foundation Center for Water and Climate Research; the Ben May Center for Chemical Theory and Computation; Scott Eric Jordan; the Yotam Project; the estate of Emile Mimran; and the European Research Council. Prof. Koren is the incumbent of the Beck / Lebovic Chair for Research in Climate Change.

Featured image: On Jan. 3, 2020, the smoke from bushfires in SE Australia were caught in satellite images beginning to move eastward. Image: Suomi National Polar-orbiting Partnership

Reference: Eitan Hirsch, Ilan Koren, “Record-breaking aerosol levels explained by smoke injection into the stratosphere”, Science  19 Mar 2021: Vol. 371, Issue 6535, pp. 1269-1274 DOI: 10.1126/science.abe1415

Provided by Weizmann Institute of Science

Human Borders Threaten Wildlife As Climate Changes (Nature)

Human-made borders like the USA-Mexico border wall could make it difficult for almost 700 mammal species to adapt to climate change.

Our scientists have identified 32,000km of borders fortified with fences and walls that could potentially stop large numbers of animals from reaching more suitable environments.

Ecologically damaging

Borders between the USA and Mexico, China and Russia and India and Myanmar could be the most ecologically damaging.

The USA-Mexico border wall alone could obstruct the movement of 122 mammal species displaced by climate change including the Mexican wolf, jaguar and jaguarundi.

Mammals that could be obstructed by human-made borders across the world include leopards, tigers, the critically endangered Saiga antelope, and cheetah.

Suitable habitats

According to our researchers, a third of mammals and birds will need to find suitable habitats in other countries by 2070 due to climate change.

This movement is most likely to happen between the Amazon rainforest and tropical Andes, around the Himalayas, and in parts of Central and Eastern Africa.

Our researchers are calling for more cross-border conservation initiatives and habitat corridors to reduce the problem.

COP 26

As well as political borders, our researchers also looked at likely impacts of ongoing climate change on species within countries.

They found that biodiversity loss is likely to be most severe in countries that are less responsible for the emissions that are driving climate change.

They are urging world leaders to reduce the risk to biodiversity by committing to ambitious reductions in greenhouse gases when they meet at the UN Climate Change Conference (COP 26) in Glasgow this November.

Featured image: Border barriers, such as this along the USA-Mexico border, present an obstacle for many species whose ranges are shifting under climate change. © Durham University

Find out more

Reference: Mark A. Titley, Stuart H. M. Butchart, Victoria R. Jones, Mark J. Whittingham, Stephen G. Willis, “Global inequities and political borders challenge nature conservation under climate change”, Proceedings of the National Academy of Sciences Feb 2021, 118 (7) e2011204118; DOI: 10.1073/pnas.2011204118

Provided by Durham University

Generating Electricity: The Price of Carbon Certificates Must Increase (Nature)

Economist at FAU has calculated which strategy is most effective for reducing CO2 emissions

Energy market researchers at FAU, the Vienna University of Economics and Business in Austria and the University of Applied Sciences of the Grisons, Switzerland, have been investigating which methods are most effective for reducing the carbon dioxide emissions created when generating electricity. They have come to the conclusion that increasing the price of carbon credits is currently considerably more effective than subsidising renewable energy from wind and solar power. The results of the study have now been published in the Journal of Environmental Economics and Management, one of the leading journals for environmental economics.

Germany aims to cut its greenhouse gas emissions by 55% by 2030, and by 2050, it hopes to be largely greenhouse gas neutral. To achieve these ambitious goals, the Federal Government is mainly using subsidies for regenerative energy sources, above all for wind and solar power. Germany uses the European Union Emissions Trading System (EU ETS) for pricing emissions, where the price for carbon certificates was significantly less than 10 euros per tonne of CO2 for several years. Even though Germany has increased the price of CO2 for heating oil and fuels to 25 euros per tonne at the beginning of the year, this does not apply to electricity generation.

Britain is following a different approach from Germany

Image: FAU

‘Less than 10 euros per tonne of carbon dioxide is simply not enough to significantly reduce emissions,’ says economist Prof. Dr. Mario Liebensteiner, Professorship of Energy Markets and Energy Systems Analysis at the School of Business, Economics and Society at FAU. In collaboration with Prof. Dr. Klaus Gugler from the Vienna University of Economics and Business and Dr. Adhurim Haxhimusa from the University of Applied Sciences of the Grisons, Prof. Liebensteiner has investigated which control instruments are most effective for cutting greenhouse gas emissions during electricity production by using Germany and Great Britain as an example. ‘Both countries are pursuing different strategies,’ says Liebensteiner. ‘Whilst Germany is offering significant subsidies for renewable energy sources, Britain has introduced a CO2 tax for the electricity market. This means that the effective price of CO2 has been increased to over 35 euros per tonne.’

Which of these measures is most effective? For their comparison, the researchers evaluated data from both countries from the last few years: daily CO2 emissions from the electricity sector, CO2 prices, electricity fed into the grid from renewable energy sources and other variables such as the demand for electricity, the price of coal and gas, and seasonal effects. The results were clear. While Germany only achieved a moderate reduction in emissions in the electricity sector, Great Britain has cut its emissions by 55 percent after introducing the tax on electricity in 2013.

Gas is replacing coal

Image: FAU

The researchers say that this difference is caused by two central aspects. On the one hand, subsidies for renewable energies are not achieving the desired effect. When prices for CO2 are low, wind and solar power initially replace only the relatively ‘clean’ gas power stations, while ‘dirty’ coal, and mainly very dirty brown coal, can retain their share of the market to a significant extent. Electricity produced using coal is only pushed out of the market when a very high amount of renewable energy is fed into the grid. On the other hand, as is the case in Great Britain, higher taxation of carbon dioxide emissions leads to coal increasingly being replaced by gas as an energy source. ‘Gas emits about half as much CO2 as coal when producing electricity,’ explains Mario Liebensteiner. ‘A moderately high price for CO2 makes coal unprofitable and we see a drop in emissions.’

A sample calculation: What can you achieve with a billion euros?

Image: FAU

The model is very well suited for calculating the costs of approaches to climate policy. The economists calculated the extent to which governments can cut emissions with one billion euros. ‘In Germany, you can save around 20 million tonnes of CO2 due to the low carbon certificate price of eight euros per tonne,’ explains Liebensteiner. ‘If the money is invested in feed-in tariffs for wind or solar power, CO2 emissions can only be reduced by five million or one million tonnes respectively.’ The effect would be far greater in Britain. At a moderately high price of 36 euros per tonne, it would be possible to cut CO2 emissions by 33 million tonnes with one billion euros and around 18.5 million tonnes using current feed-in tariffs for wind power.

Market-based incentives require technologies to bridge the gap

According to the researchers, the decisive advantage of the British strategy is that a CO2 price produces market-based incentives and does not dictate which technology is used. This allows relatively clean gas to push coal, which is considerably more problematic, off the market to a significant extent. In contrast, considerable subsidies for renewable energies combined with a low price for CO2 leads to gas being pushed off the market first, while coal power stations remain in operation. ‘Our results demonstrate that even a moderately high price for CO2 can help to reduce large amounts of CO2 quickly and cheaply if gas power stations are available to bridge the gap,’ says Liebensteiner. ‘We ought to bear in mind, however, that gas is also a fossil fuel and should be replaced by alternative sources in the long term, of course.’

Further information

Klaus Gugler, Adhurim Haxhimusa, Mario Liebensteiner, “Effectiveness of climate policies: Carbon pricing vs. subsidizing renewables”, Journal of Environmental Economics and Management, Volume 106, 2021, 102405,
ISSN 0095-0696,

Provided by FAU

Modeling Rainfall Drop By Drop (Nature)

A high-frequency model developed using data from new high-precision rain gauges gives fresh insight into the dynamics of rain and runoff events.

Using a network of a newly introduced type of rain gauge that can measure rainfall with drop-by-drop precision, KAUST researchers have developed a high-frequency rainfall model to improve understanding of rainfall/runoff dynamics, such as flash flooding and hydrodynamics in small watersheds.

A high-frequency rainfall model has been developed to improve understanding of rainfall dynamics. © Tetra Images/ Getty Images

Rainfall modeling is one of the core aspects of weather forecasting and is often used to predict other weather parameters, such as wind and solar irradiance. Yet the power and insight of such models are limited by the data used to construct them. When it comes to precipitation, this means that modelers have to rely on sparse recordings of rainfall at 6-15-minute intervals at best, but more often hourly intervals. This leads to a “smoothing” of rainfall over time and a loss of information about how much rain falls during each rainfall event, which is a problem, according to Ph.D. student Yuxiao Li.

“This assumption is not appropriate for modeling precipitation at high frequency because large quantities of rainfall in the past can result in an unrealistically high probability of rainfall occurrence in such models,” explains Li. “In this study, we used the high-frequency rainfall data collected by new instruments called Pluvimate rain gauges to better reproduce the statistical properties of precipitation occurrence, intensity and dry-spell duration.”

The new acoustic rain gauges, which record each drop of rain caught in a receptacle, can provide precise high-frequency rainfall data, which are impossible to acquire using classical measurement devices such as tipping-bucket rain gauges and radar. These new datasets provide unprecedented insight into the minute-to-minute dynamics of rainfall, which requires a change in the statistical modeling approach.

“High-frequency precipitation data include more zeros and have longer ‘tails’ to high rainfall intensities than common precipitation data,” says Li. “We developed a model that can capture this ‘skewness’ and the heavy tail of the high-frequency precipitation data, allowing us to generate synthetic precipitation data that provides valuable information for water management, especially at unobserved times and locations.”

The model developed by Li and his supervisor Ying Sun also includes meteorological representations of ground and atmospheric layers, which allows direct physical interpretation of the statistical characteristics.

“Precipitation modeling is one of the main research topics in our Environmental Statistics Group,” says Li. “Our model is the first stochastic precipitation generator for high-frequency precipitation and will be valuable for analyzing many short-term phenomena, as well as forming the basis for a ‘digital twin’ model to reproduce physical processes using a virtual replica, which is a hot topic for smart cities and industry 4.0.”

References: Li, Y. & Sun, Y. A multi-site stochastic weather generator for high-frequency precipitation using censored skew-symmetric distribution. Spatial Statistics, 100474 (2020).

Provided by KAUST

New Computer Program Predicts Future Extinctions (Biology / Nature)

A new computer program for predicting future species extinctions has been developed as part of a PhD thesis at the University of Gothenburg.

Tobias Andermann, PhD student at the Department of Biological and Environmental Sciences is part of a research team that works with software development. The team has made it their mission to produce computer programs that enable modern biologists to work with a broad range of new technologies and with large datasets.

Types of data that can be derived from a single specimen. The displayed specimen is a critically endangered (CR) Verreaux’s sifaka (Propithecus verreauxi). Photographed in the Kirindy reserve in Western Madagascar. Photo: Tobias Andermann

Based on public data

Tobias Andermann now presents some of the latest programs in his doctoral dissertation. One of these programs is designed to predict future species extinctions. The program is based on publicly available data.

“It is amazing how much freely available data is stored in online databases and we are only beginning to fully utilize the potential of these data. This can for example be data about where species were sighted and information about how threatened with extinction a species is. All of this information can be used in our evolutionary models to predict the most likely future for a given species,” says Tobias Andermann.

It is important to predict future extinctions

Predicting future extinctions and extinction risks is something that is of the utmost importance, Tobias Andermann believes.

“We are in the middle of an unfolding mass extinction and in order to counteract this trend, it is crucial for us to be able to predict when, where, and which species are likely to go extinct.”

“Our program can also be used to simulate the effects of specific conservation strategies and the results give us hope. We can make a huge positive impact if we act now.”

Another program for large DNA datasets

A program that helps evolutionary biologists to analyze the enormous amounts of data produced with new DNA sequencing technologies is also presented in Tobias Andermann’s PhD thesis.

“The amount of data you receive from modern DNA sequencing machines is simply overwhelming. We are talking about billions of DNA nucleotides that these machines can produce for a single sample, all scattered across millions of short sequences. Researchers then need to put this gigantic puzzle back together to be able to work with these data. That’s exactly where our new program comes in,” says Tobias Andermann.

The program has been downloaded more than 19,000 times within a short time frame by researchers and students from around the world.

References: Ander mann, Tobias, “Advancing Evolutionary Biology: Genomics, Bayesian Statistics, and Machine Learning”, 2020. ISBN: 978-91-8009-136-7 978-91-8009-137-4

Provided by University of Gothenburg

The Melting Of the Greenland Ice Sheet Could Lead To a Sea Level Rise of 18 cm In 2100! (Nature)

A new study, headed by researchers from the Universities of Liège and Oslo, applying the latest climate models, of which the MAR predicts a 60% greater melting of the Greenland ice sheet than previously predicted. Data that will be included in the next IPCC report. This study is published in Nature Communications.

Evolution of the surface mass balance (snowfall – melting) with the old (cmip5) and new (cmip6) scenarios. The blue colour indicates a mass loss in mm/year ©Université de Liège / X.Fettweis

The Greenland ice sheet, the second largest after the Antarctic’s, covers an area of 1.7 million square kilometres. Its total melting could lead to a significant rise in ocean levels, up to 7 metres. Although we are not there yet, the previous scenarios predicted by climate models have just been revised upwards, predicting a rise in sea levels of up to 18 cm by 2100 (compared to the 10 cm announced previously) just because of the increase in surface melting. Within the framework of the next IPCC report (AR6) which will appear in 2022, the University of Liège Laboratory of climatology has been led to apply, within the framework of the ISMIP6 project, the MAR climate model which it is developing to downscale the old and new IPCC scenarios. The results obtained showed that for the same evolution of greenhouse gas concentrations till 2100, these new scenarios predict a 60% greater surface melting of the Greenland ice cap than previously estimated for the previous IPCC report (AR5, 2013).

The MAR model was the first to demonstrate that the Greenland ice sheet would melt further with a warming of the Arctic in summer. While our MAR model suggested that in 2100 the surface melting of the Greenland ice sheet would contribute to a rise in the oceans of around ten centimetres in the worst-case scenario (i.e. if we do not change our habits),” explains Stefan Hofer, post-doc researcher at the University of Oslo, “our new projections now suggest a rise of 18 cm”. As the new IPCC scenarios are based on models whose physics have been improved – in particular by incorporating a better representation of cloudiness – and whose spatial resolution has been increased, these new projections should in theory be more robust and reliable.

The team of the Laboratory of Climatology was the first to downscale these scenarios on the Greenland ice cap. “It would now be interesting, says Xavier Fettweis, researcher and director of the Laboratory, to analyse how these future projections are sensitive to the MAR model that we are developing by downscalling these scenarios with other models than MAR as we have done on the present climate (GrSMBMIP)”. This study will be carried out within the framework of the European project PROTECT (H2020). The objective of this project is to assess and project changes in the terrestrial cryosphere, with fully quantified uncertainties, in order to produce robust global, regional and local projections of sea level rise over a range of time scales. https://protect-slreu/

The data collected as part of the Katabata project, launched last September by Xavier Fettweis and his colleague Damien Ernst, will also help to refine the models, particularly the wind model-ling in the MAR climate model. “Knowing that the wind influences the melting of the ice sheet, it is important to have the most reliable models possible, concludes Xavier Fettweis.”

References: (1) Stefan Hofer et al.: Greater Greenland Ice Sheet contribution to global sea level rise in CMIP6, Nature Communications, 15 December 2020. (2) Fettweis et al.: GrSMBMIP: intercomparison of the modelled 1980-2012 surface mass balance over the Greenland Ice Sheet, The Cryosphere, 14, 3935-3958,, 2020.

Provided by University of Liege

Pandemic Brings Record Fall in Global CO2 Emissions (Nature)

The Global Carbon Project, of which LMU geographer Julia Pongratz is a leading member, reports an unprecedented drop in the level of carbon emissions since the onset of the coronavirus pandemic, although the overall concentration of CO2 in the atmosphere continues to rise.

In the USA and the EU reductions in the use of coal were complemented by the effects of the restrictions imposed in response to the coronavirus pandemic. Photo: imago images / Sven Simon

According to the latest figures published by the Global Carbon Project (GCP), the current coronavirus pandemic has led to a significant reduction in global CO2 emissions. The GCP is an international collaboration of climate researchers, which includes LMU geographers Julia Pongratz, Selma Bultan and Kerstin Hartung as contributors. The group monitors both the amounts of greenhouse gases released into Earth‘s atmosphere and the quantities absorbed by the world’s oceans and sequestered in vegetation on land.

The latest report issued by the GCP shows that, 5 years after the conclusion of the Paris Agreement, the rate of increase in global CO2 emissions has slowed. In the decade from 2010 to 2019, CO2 emissions from fossil sources decreased significantly in 24 countries whose economies had grown over the same period. This result suggests that policies intended to mitigate climate change may be having an effect. Over the course of this year – in part owing to the measures introduced in response to the coronavirus pandemic – global emissions of fossil carbon are estimated to have fallen to 34 billion tons (34 Gt CO2). This figure represents a decrease of some 2.4 Gt from the previous year. This is a considerably larger drop than previous dips in the emission record for the years 1981 and 2009 (0.5 Gt), 1992 (0.7 Gt) and 1945 (0.9 Gt). In order to achieve the goals set out in the Paris Agreement, CO2 emissions must fall by between 1 and 2 Gt annually between now and 2030.

The decrease was particularly notable in the USA (-12%) and in member states of the EU (-11%). “In both cases, reductions in the use of coal were complemented by the effects of the restrictions imposed in response to the coronavirus pandemic,” says Pongratz. “In 2019, the rate of increase in CO2 emissions was slower than in previous years. As a consequence of the pandemic, emissions have now fallen significantly. This makes 2020 a crucial year, but whether it marks the start of a trend strongly depends on how the measures taken to stimulate the economy unfold around the world. We are already seeing signs that the emission rate is climbing back toward the level observed for 2019.”

The transport sector accounts for most of the fall

Most of the decrease recorded for 2020 can be attributed to a drop in the carbon footprint of the transport sector. In December 2020, emissions due to road and air traffic still were lower by about 10% and 40%, respectively, relative to 2019 values. The authors of the report emphasize that it is not yet possible to assess whether the rate of global emissions will continue to fall in the coming years. Following the decrease in emissions in the aftermath of the global financial crisis in 2008, emissions rebounded a massive 5% in 2010, as the global economy recovered. The fear is that this could happen also in 2021.

Overall, total emissions of CO2 – from fossil sources and land use – for 2020 are estimated to be on the order of 39 Gt, which approximately corresponds to the value recorded for the year 2012. This caused the CO2 concentration of the atmosphere to continue rising, and the average concentration for the current year is expected to set a new record of 412 ppm (parts per million). This corresponds to a rise of 48% relative to the pre-industrial level. The authors of the new report point out that the atmospheric CO2 level, and consequently the world’s climate, will only stabilize when global CO2 emissions are near zero.

The overall amount of CO2 absorbed by carbon sinks on land and in the oceans continues to rise, and in 2020, they sequestered some 54% of all anthropogenic CO2 emissions.

No significant decrease in emissions from land use change

Julia Pongratz is particularly interested in the impact of changes in land use on the global carbon balance. While unusually high level of emissions from these sources were estimated for 2019 – which were exacerbated by extraordinarily dry conditions in Indonesia and the highest rate of deforestation in the Amazon Basin since 2008 – the value for 2020 is lower again and equivalent to the mean level for the decade as a whole.

“For the first time, we were able to estimate the gross CO2 emissions and removals through land use changes on the global carbon budget in 2020,” Pongratz says. She and her colleagues come to the conclusion that this factor – largely attributable to deforestation – accounts for the release of around 16 Gt of CO2 per year during the past decade. On the other hand, removals of CO2 such as through the abandonment of agricultural lands, over the same period resulted in an estimated increase of nearly 11 Gt in CO2 sequestration capacity. The net balance of +6 Gt for 2020 is similar to the values for previous years. “We have not found a reduction in carbon emissions in this sector yet. Deforestation continues at a rapid pace, especially in tropical regions, and public awareness of the impact of agricultural emissions has been muted owing to the influence of Covid,” Pongratz says. “Effective measures to improve land management could not only curb deforestation, they could also contribute to an increase in CO2 uptake from the atmosphere by allowing for the regrowth of natural vegetation.”

The team of 86 climate researchers from all parts of the world publishes its study in the peer-reviewed journal Earth System Science Data. The Global Carbon Budget 2020 is the 15th edition of the annual update that started in 2006. Besides Julia Pongratz, Selma Bultan und Kerstin Hartung, scientists from 7 other German institutions contributed — the Alfred-Wegener-Institut (Bremerhaven), the Max Planck Institute for Meteorology (Hamburg), the Max Planck Institute for Biogeochemistry (Jena), the Karlsruhe Institute of Technology, the GEOMAR Helmholtz Centre for Ocean Research (Kiel) and the Leibniz-Institut für Ostseeforschung (Warnemünde).

Further information
Data and Figures 
Data Atlas 
Estimated Daily Emission Rates 

Provided by LMU Munich

Clean Air Act Saved 1.5 Billion Birds (Nature)

Improved air quality, reduced ozone pollution may have averted bird deaths.

U.S. pollution regulations meant to protect humans from dirty air are also saving birds. So concludes a new continentwide study published today in The Proceedings of the National Academy of Sciences. Study authors found that improved air quality under a federal program to reduce ozone pollution may have averted the loss of 1.5 billion birds during the past 40 years. That’s nearly 20 percent of birdlife in the United States today. The study was conducted by scientists at Cornell University and the University of Oregon.

Great Blue Heron in front of an oil refinery. ©Gerrit Vyn

“Our research shows that the benefits of environmental regulation have likely been underestimated,” says Ivan Rudik, a lead author and Ruth and William Morgan Assistant Professor at Cornell’s Dyson School of Applied Economics and Management. “Reducing pollution has positive impacts in unexpected places and provides an additional policy lever for conservation efforts.”

Ozone is a gas that occurs in nature and is also produced by human activities, including by power plants and cars. It can be good or bad. A layer of ozone in the upper atmosphere protects the Earth from the harmful ultraviolet rays of the sun. But ground-level ozone is hazardous and is the main pollutant in smog.

To examine the relationship between bird abundance and air pollution, the researchers used models that combined bird observations from the Cornell Lab of Ornithology’s eBird program with ground-level pollution data and existing regulations. They tracked monthly changes in bird abundance, air quality, and regulation status for 3,214 U.S. counties over a span of 15 years. The team focused on the NOx (nitrogen oxide) Budget Trading Program, which was implemented by the U.S. Environmental Protection Agency to protect human health by limiting summertime emissions of ozone precursors from large industrial sources.

Blackburnian Warbler. ©Ian Davies

Study results suggest that ozone pollution is most detrimental to the small migratory birds (such as sparrows, warblers, and finches) that make up 86 percent of all North American landbird species. Ozone pollution directly harms birds by damaging their respiratory system, and indirectly affects birds by harming their food sources.

“Not only can ozone cause direct physical damage to birds, but it also can compromise plant health and reduce numbers of the insects that birds consume,” explains study author Amanda Rodewald, Garvin Professor at the Cornell Department of Natural Resources and the Environment and Director of the Center for Avian Population Studies at the Cornell Lab of Ornithology. “Not surprisingly, birds that cannot access high-quality habitat or food resources are less likely to survive or reproduce successfully. The good news here is that environmental policies intended to protect human health return important benefits for birds too.”

Last year, a separate study by the Cornell Lab of Ornithology showed that North American bird populations have declined by nearly 3 billion birds since 1970 (Rosenberg et. al. Science, 2019). This new study shows that without the regulations and ozone-reduction efforts of the Clean Air Act, the loss of birdlife may have been 1.5 billion birds more.

“This is the first large-scale evidence that ozone is associated with declines in bird abundance in the United States and that regulations intended to save human lives also bring significant conservation benefits to birds,” says Catherine Kling, Tisch University Professor at the Cornell Dyson School of Applied Economics and Management and Faculty Director at Cornell’s Atkinson Center for Sustainability. “This work contributes to our ever increasing understanding of the connectedness of environmental health and human health.”

References: Yuanning Liang, Ivan Rudik, Eric Zou, Alison Johnston, Amanda D. Rodewald, Catherine L. Kling. Conservation Co-Benefits from Air Pollution Regulation: Evidence from Birds. The Proceedings of the National Academy of Sciences, November 2020.