Ice age climate analysis reduces worst-case warming expected from rising CO2

As carbon dioxide accumulates in the atmosphere, the Earth will get hotter. But exactly how much warming will result from a certain increase in CO2 is under study. The relationship between CO2 and warming, known as climate sensitivity, determines what future we should expect as CO2 levels continue to climb.

New research led by the University of Washington analyzes the most recent ice age, when a large swath of North America was covered in ice, to better understand the relationship between CO2 and global temperature. It finds that while most future warming estimates remain unchanged, the absolute worst-case scenario is unlikely.

The open-access study was published April 17 in Science Advances.

"The main contribution from our study is narrowing the estimate of climate sensitivity, improving our ability to make future warming projections," said lead author Vince Cooper, a UW doctoral student in atmospheric sciences. "By looking at how much colder Earth was in the ancient past with lower levels of greenhouse gases, we can estimate how much warmer the current climate will get with higher levels of greenhouse gases."

The new paper doesn't change the best-case warming scenario from doubling CO2 -- about 2 degrees Celsius average temperature increase worldwide -- or the most likely estimate, which is about 3 degrees Celsius. But it reduces the worst-case scenario for doubling of CO2 by a full degree, from 5 degrees Celsius to 4 degrees Celsius. (For reference, CO2 is currently at 425 ppm, or about 1.5 times preindustrial levels, and unless emissions drop is headed toward double preindustrial levels before the end of this century.)

As our planet heads toward a doubling of CO2, the authors caution that the recent decades are not a good predictor of the future under global warming. Shorter-term climate cycles and atmospheric pollution's effects are just some reasons that recent trends can't reliably predict the rest of this century.

"The spatial pattern of global warming in the most recent 40 years doesn't look like the long-term pattern we expect in the future -- the recent past is a bad analog for future global warming," said senior author Kyle Armour, a UW associate professor of atmospheric sciences and of oceanography.

Instead, the new study focused on a period 21,000 years ago, known as the Last Glacial Maximum, when Earth was on average 6 degrees Celsius cooler than today. Ice core records show that atmospheric CO2 then was less than half of today's levels, at about 190 parts per million.

"The paleoclimate record includes long periods that were on average much warmer or colder than the current climate, and we know that there were big climate forcings from ice sheets and greenhouse gases during those periods," Cooper said. "If we know roughly what the past temperature changes were and what caused them, then we know what to expect in the future."

Researchers including co-author Gregory Hakim, a UW professor of atmospheric sciences, have created new statistical modeling techniques that allow paleoclimate records to be assimilated into computer models of Earth's climate, similar to today's weather forecasting models. The result is more realistic temperature maps from previous millennia.

For the new study the authors combined prehistoric climate records -- including ocean sediments, ice cores, and preserved pollen -- with computer models of Earth's climate to simulate the weather of the Last Glacial Maximum. When much of North America was covered with ice, the ice sheet didn't just cool the planet by reflecting summer sunlight off the continents, as previous studies had considered.

By altering wind patterns and ocean currents, the ice sheet also caused the northern Pacific and Atlantic oceans to become especially cold and cloudy. Analysis in the new study shows that these cloud changes over the oceans compounded the glacier's global cooling effects by reflecting even more sunlight.

In short, the study shows that CO2 played a smaller role in setting ice age temperatures than previously estimated. The flipside is that the most dire predictions for warming from rising CO2 are less likely over coming decades.

"This paper allows us to produce more confident predictions because it really brings down the upper end of future warming, and says that the most extreme scenario is less likely," Armour said. "It doesn't really change the lower end, or the average estimate, which remain consistent with all the other lines of evidence."

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Tropical birds could tolerate warming better than expected, study suggests

Consider the globe, spinning silently in space. Its poles and its middle, the equator, remain relatively stable, thermally speaking, for the duration of Earth's annual circuit around the sun. The spaces between -- Earth's temperate zones -- experience seasons, with their characteristic temperature extremes.

It would follow that animals that evolved in each of these zones should match them, physiologically. We expect tropical animals to handle a certain degree of heat, but not wild swings in temperature. That seems to be the case for tropical ectotherms, or "cold-blooded" animals such as amphibians, reptiles, and insects. However, in a first-of-its-kind study of "warm-blooded" endotherms, a University of Illinois Urbana-Champaign team found tropical birds can handle thermal variation just fine.

"We tested the climate variability hypothesis, which predicts that organisms can't handle variation because they haven't seen it over evolutionary time," said study co-author Jeff Brawn, professor emeritus in the Department of Natural Resources and Environmental Sciences (NRES), part of the College of Agricultural, Consumer and Environmental Sciences (ACES) at Illinois. "That may be true for ectotherms, but the evidence is just not there yet for birds in the Neotropics. Now we know they're able to handle it."

Climate change may increase the average annual temperature in the tropics, as well as in microclimates like forest edges or tree canopies. The study provides some reassurance that, at least when looking at temperature alone, tropical birds should be okay. Why does that matter?

"The Neotropics alone are home to 40% of the world's bird species. Anyone who cares about birds should care about what's happening in the tropics," Brawn said. "Also, birds are important for the overall integrity of tropical forest systems, holding down insect populations that could damage trees."

Brawn and co-author Henry Pollock, who did postdoctoral research in NRES, already showed that both temperate and tropical birds can withstand temperature extremes, disproving the climate variability hypothesis across latitudes. Their new study explains whether variation within habitats matters for specific groups of tropical birds.

Many tropical birds spend their lives deep in the forest understory. Their large eyes suggest they're well adapted to the dark, where temperatures stay relatively cool and stable. Conversely, other bird groups zip between the forest canopy and its floor, or in and out of forest gaps and edges. These birds, Pollock reasoned, might have more tolerance to temperature fluctuations than their understory counterparts.

He captured birds from 89 species in Panama and, using a technique called respirometry, measured their metabolic rates across a range of temperatures. The birds were safely cooled and returned to their habitats after testing. He also took advantage of long-term weather station data provided by the Smithsonian Tropical Research Institute to document temperature differences across forest microclimates.

"If you measure temperature in an open area versus in the forest, there are large differences," said Pollock, now the executive director of the Southern Plains Land Trust. "But we did not find any evidence that those differences translated into greater temperature tolerance among groups of tropical birds."

Long-term observations indicate that when tropical forests become fragmented due to deforestation, an increasing phenomenon, certain groups of birds are more likely to decline. Insect-eating understory birds are among the hardest hit. For decades, tropical ornithologists believed narrow temperature tolerances may have been to blame for the declines of understory birds, but this study suggests otherwise.

Pollock is quick to point out that he only measured one aspect of an organism's thermal environment. In the real world, temperature doesn't increase in isolation; typically, when temperature goes up, so does solar radiation. Humidity and precipitation come into play, as well. And all of these things are part of the equation with habitat loss and climate change.

Still, one aspect of the climate variability and microclimate hypotheses can, for now, be put to rest for tropical birds.

"There's very little good news for tropical birds these days, but it's comforting that we've eliminated one factor as to what may go wrong with climate change. It's actually not a surprise; birds are very adaptable," Brawn said. "Heat tolerance alone presents an incomplete situation, but this is further empirical evidence that, if it does get warmer, tropical birds may be able to tolerate a certain level of that."

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Greenland's ice sheet is melting -- and being replaced by vegetation

An estimated 11,000 sq miles or 28,707 sq kilometres of Greenland's ice sheet and glaciers have melted over the last three decades, according to a major analysis of historic satellite records.

The total area of ice loss is equivalent to the size of Albania, and represents about 1.6 % of Greenland's total ice and glacier cover.

Where there was once ice and snow, there is now barren rock, wetlands and areas of shrub.

A team of scientists from the University of Leeds, who have tracked the changes across Greenland from the 1980s through to the 2010s, say warmer air temperatures are causing the ice to retreat, which in turn is having an impact on the temperature of the land surface, greenhouse gas emissions and the stability of the landscape.

Permafrost -- a permanently frozen layer below the Earth's surface -- is being "degraded" by the warming and in some areas, the scientists warn that it could have an impact on the infrastructure, buildings and communities that exist above it.

Their findings -- "Land cover changes across Greenland dominated by a doubling of vegetation in three decades"- are reported today (13/02) in the journal Scientific Reports.

Impact of global warming

Greenland is part of the Arctic region. It is the world's biggest island, around 836,330 sq miles in size (2.1 million sq km). Most of the land is covered by ice and glaciers and it is home to almost 57,000 people.

Since the 1970s, the region has been warming at double the global mean rate. On Greenland, average annual air temperatures between 2007 and 2012 were 3 degrees C warmer, compared with the 1979 to 2000 average.

And the researchers warn that more extreme temperatures are likely in the future.

Jonathan Carrivick, an Earth scientist based in the Faculty of Environment at Leeds and one of the authors of the study, said: "Warmer temperatures are linked to the land cover changes that we are seeing on Greenland.

"By analysing high resolution satellite images, we have been able to produce a detailed record of the land cover changes that are taking place."

Ice disappears to be replaced by bare rock and shrubs

Ice loss was concentrated around the edges of present-day glaciers but also in the north and south- west of Greenland. There were also high-levels of ice loss in localised areas in the west, mid-north-west and south-east.

Over the three decades, the amount of land with vegetation growing on it increased by 33,774 sq miles (87,475 sq km), more than doubling over the study period.

A pronounced increase in vegetation was seen across the south-west, east and north-east. The greatest increase in dense wetland vegetation occurred in the vicinity of Kangerlussuaq in the south-west and in isolated areas in the north-east.

Analysis by the researchers revealed that vegetation had increased along a latitudinal gradient between 63 degrees North and 69 degrees North and declined north of this.

Jonathan Carrivick said: "We have seen signs that the loss of ice is triggering other reactions which will result in further loss of ice and further 'greening' of Greenland, where shrinking ice exposes bare rock that is then colonised by tundra and eventually shrub.

"At the same time, water released from the melting ice is moving sediment and silt, and that eventually forms wetlands and fenlands."

Loss of ice triggers further warming

The loss of ice affects land surface temperatures because of albedo, which is the measure of how reflective a surface is.

Snow and ice are good reflectors of the sun's energy hitting the Earth's surface and this helps to keep the Earth cooler. As the ice retreats, it exposes bedrock which absorbs more solar energy, raising the temperature of the land surface.

Similarly, as ice melts it increases the quantity of water in lakes. Water absorbs more solar energy than snow and this also increases the temperature of the land surface.

Greenhouse gas emitter

The analysis shows a near quadrupling of wetlands across Greenland, particularly in the east and north-east. The wetlands are a source of methane emissions.

Writing in the paper, the researchers noted: "Expansion of vegetation and especially in wetland areas indicates but also exacerbates permafrost thaw, active layer thickening and thus emissions of greenhouse gasespreviously stored in these Arctic soils."

The researchers also developed a model to predict those areas on Greenland that are likely to see "marked and accelerated" change in the future.

Dr Michael Grimes, the lead author of the report who conducted the research as part of their PhD, added: "The expansion of vegetation, occurring in tandem with the retreat of glaciers and the ice sheet, is significantly altering the flow of sediments and nutrients into coastal waters.

"These changes are critical, particularly for the indigenous populations whose traditional subsistence hunting practices rely on the stability of these delicate ecosystems.

Read more at Science Daily

Predicting saltwater intrusion into groundwater using Plymouth, Mass. as test case

As the world warms and ice sheets melt, the ocean continually rises. The greater Boston area can expect to see between one and six feet of sea level rise by 2100, according to recent estimates. To find out what this rise might mean for freshwater supplies, a team of hydrogeologists from the University of Massachusetts Amherst, led by David Boutt, professor of Earth, geographic and climate sciences, partnered with the Southeastern Massachusetts Pine Barrens Alliance (SEMPBA) and 13 other grassroots environmental organizations to develop an innovative new model that can not only predict saltwater intrusion over the next 75 years, but also pinpoint the main sources of salt contamination today -- road salt and human development. The team released the results of their study in the recent report, Saltwater Intrusion Vulnerability Assessment in Plymouth, MA.

"For many years now, I've been working with citizen stakeholders in the southeastern corner of Massachusetts," says Boutt, "and in 2021, the Pine Barrens Alliance, an environmental group interested in preserving the area's unique environmental character, approached me with an idea for a project to help assess how communities along the coast could best prepare for climate change."

Boutt and his colleagues, including recent UMass graduate and research assistant Alexander Kirshen, undergraduates Rachel King and Carly Lombardo, graduate student Daniel Corkran and postdoctoral researcher Brendan Moran, jumped at the opportunity to apply their academic research to an urgent, real-world problem close to home.

Plymouth sits on top of a freshwater aquifer -- the town's sole source of water. Because Plymouth extends to the ocean's edge, it is extremely susceptible to rising sea levels. For their study, Boutt, Kirshen and colleagues peeked underground to see what was happening.

Groundwater, flowing beneath the surface of the land, and the ocean's water, which, likewise, flows subterraneanly, push against each other and reach an equilibrium state. A well sunk on the freshwater side will flow with sweet water, but one that drills down into the brackish meeting point between fresh and salt will come up briny. As the oceans rise, that sub-surface saltwater pushes farther inland, and wells that have delivered pure water for generations can suddenly turn salty.

While the theory might seem intuitive enough, actually mapping, to say nothing of predicting, the flows and interactions of both fresh and salt water is an enormously complex task.

To start, the team built a salinity database that gathered all the available data from groundwater wells and surface water, such as ponds and streams, in the Plymouth area and measured them for salinity. This gave them a baseline understanding of the current locations and likely sources of elevated water salinity.

Next, Boutt and Kirshen adopted an existing U.S. Geological Survey hydrogeological model, which only focused on the onshore half of the hydrogeology equation, by extending its reach five kilometers offshore. The model includes ponds, streams, terrestrial recharge -- or the rate and amount of precipitation that seeps down into the aquifer -- as well the various wells that draw from the aquifer and the wastewater that is returned to the aquifer via re-infiltration or septic systems.

Finally, they conducted a series of model runs that took into consideration various scenarios in terms of future precipitation, sea-level rise, groundwater usage and changes in water returned to the aquifer.

"We found that, under the high sea-level rise scenario, areas of the aquifer will increase in salinity by up to 17,000 milligrams per liter by 2100," says Kirshen, "and the mixing zone between the ocean and freshwater will migrate inland by up to 200 meters." While a few ponds might see significant rise in water elevation, by up to 1.8 meters, most ponds would not see their salinity increase from this source of salinization.

The team also learned that water returned to the aquifer by septic systems plays a major role in helping to limit saltwater intrusion. "About 66% of the water that gets pumped out of the aquifer ends up returning to it," says Kirshen.

Perhaps the biggest surprise is that the highest levels of salinity today aren't near the coast, but inland, and especially around the roads. "This surprised me," says Boutt, "and it looks like road salt is one of the main sources of elevated salinity today."

"In partnering with UMass Amherst, we were always thinking beyond the municipal boundaries of Plymouth," says SEMPBA Vice President Frank Mand. "We share an aquifer and a geological foundation with over 30 communities in our ecoregion. So, though the news for Plymouth is good, more importantly we now have a scientific foundation -- and new methods for evaluating susceptibility to saltwater intrusion -- that are transferrable to those other communities and will help inform Plymouth's and other communities' planning for years to come."

"We were not looking to science to help us recover from our mistakes," Mand adds. "We were seeking to avoid problems in the future. That, in and of itself, was a worthy goal."

Read more at Science Daily

Window to avoid 1.5°C of warming will close before 2030 if emissions are not reduced

Without rapid carbon dioxide emission reductions, the world has a 50% chance of locking in 1.5°C of warming before 2030, according to a study led by Imperial College London researchers.

The study, published today in Nature Climate Change, is the most up-to-date and comprehensive analysis of the global carbon budget. The carbon budget is an estimate of the amount of carbon dioxide emissions that can be emitted while keeping global warming below certain temperature limits.

The Paris Agreement aims to limit global temperature increase to well below 2°C above preindustrial levels and pursue efforts to limit it to 1.5°C. The remaining carbon budget is commonly used to assess global progress against these targets.

The new study estimates that for a 50% chance of limiting warming to 1.5°C, there are less than 250 gigatonnes of carbon dioxide left in the global carbon budget.

The researchers warn that if carbon dioxide emissions remain at 2022 levels of about 40 gigatonnes per year, the carbon budget will be exhausted by around 2029, committing the world to warming of 1.5°C above preindustrial levels.

The finding means the budget is less than previously calculated and has approximately halved since 2020 due to the continued increase of global greenhouse gas emissions, caused primarily from the burning of fossil fuels as well as an improved estimate of the cooling effect of aerosols, which are decreasing globally due to measures to improve air quality and reduce emissions.

Dr Robin Lamboll, research fellow at the Centre for Environmental Policy at Imperial College London, and the lead author of the study, said: "Our finding confirms what we already know -- we're not doing nearly enough to keep warming below 1.5°C.

"The remaining budget is now so small that minor changes in our understanding of the world can result in large proportional changes to the budget. However, estimates point to less than a decade of emissions at current levels.

"The lack of progress on emissions reduction means that we can be ever more certain that the window for keeping warming to safe levels is rapidly closing."

Dr Joeri Rogelj, Director of Research at the Grantham Institute and Professor of Climate Science & Policy at the Centre for Environmental Policy at Imperial College London, said: "This carbon budget update is both expected and fully consistent with the latest UN Climate Report.

"That report from 2021 already highlighted that there was a one in three chance that the remaining carbon budget for 1.5°C could be as small as our study now reports.

"This shows the importance of not simply looking at central estimates, but also considering the uncertainty surrounding them."

The study also found that the carbon budget for a 50% chance of limiting warming to 2°C is approximately 1,200 gigatonnes, meaning that if carbon dioxide emissions continue at current levels, the central 2°C budget will be exhausted by 2046.

There has been much uncertainty in calculating the remaining carbon budget, due to the influence of other factors, including warming from gasses other than carbon dioxide and the ongoing effects of emissions that are not accounted for in models.

The new researchused an updated dataset and improved climate modelling compared to other recent estimates, published in June, characterising these uncertainties and increasing confidence around the remaining carbon budget estimates.

The strengthened methodology also gave new insights into the importance of the potential responses of the climate system to achieving net zero.

'Net zero' refers to achieving an overall balance between global emissions produced and emissions removed from the atmosphere.

According to the modelling results in the study, there are still large uncertainties in the way various parts of the climate system will respond in the years just before net zero is achieved.

It is possible that the climate will continue warming due to effects such as melting ice, the release of methane, and changes in ocean circulation.

However, carbon sinks such as increased vegetation growth could also absorb large amounts of carbon dioxide leading to a cooling of global temperatures before net zero is achieved.

Dr Lamboll says these uncertainties further highlight the urgent need to rapidly cut emissions. "At this stage, our best guess is that the opposing warming and cooling will approximately cancel each other out after we reach net zero.

"However, it's only when we only when we cut emissions and get closer to net zero that we will be able to see what the longer-term heating and cooling adjustments will look like.

Read more at Science Daily

Climate-driven extreme heat may make parts of Earth too hot for humans

If global temperatures increase by 1 degree Celsius (C) or more than current levels, each year billions of people will be exposed to heat and humidity so extreme they will be unable to naturally cool themselves, according to interdisciplinary research from the Penn State College of Health and Human Development, Purdue University College of Sciences and Purdue Institute for a Sustainable Future.

Results from a new article published today (Oct. 9) in Proceedings of the National Academy of Sciences indicated that warming of the planet beyond 1.5 C above preindustrial levels will be increasingly devastating for human health across the planet.

Humans can only withstand certain combinations of heat and humidity before their bodies begin to experience heat-related health problems, such as heat stroke or heart attack. As climate change pushes temperatures higher around the world, billions of people could be pushed beyond these limits.

Since the start of the industrial revolution, when humans began to burn fossil fuels in machines and factories, temperatures around the world have increased by about 1 C, or 1.8 degrees Fahrenheit (F). In 2015, 196 nations signed the Paris Agreement which aims to limit worldwide temperature increases to 1.5 C above pre-industrial levels.

The researcher team modeled global temperature increases ranging between 1.5 C and 4 C -- considered the worst-case scenario where warming would begin to accelerate -- to identify areas of the planet where warming would lead to heat and humidity levels that exceed human limits.

"To understand how complex, real-world problems like climate change will affect human health, you need expertise both about the planet and the human body," said co-author W. Larry Kenney, professor of physiology and kinesiology, the Marie Underhill Noll Chair in Human Performance at Penn State and co-author of the new study. "I am not a climate scientist, and my collaborators are not physiologists. Collaboration is the only way to understand the complex ways that the environment will affect people's lives and begin to develop solutions to the problems that we all must face together."

A threat to billions

The ambient wet-bulb temperature limit for young, healthy people is about 31 C, which is equal to 87.8 F at 100% humidity, according to work published last year by Penn State researchers. However, in addition to temperature and humidity, the specific threshold for any individual at a specific moment also depends on their exertion level and other environmental factors, including wind speed and solar radiation. In human history, temperatures and humidity that exceed human limits have been recorded only a limited number of times -- and only for a few hours at a time -- in the Middle East and Southeast Asia, according to the researchers.

Results of the study indicate that if global temperatures increase by 2 C above pre-industrial levels, the 2.2 billion residents of Pakistan and India's Indus River Valley, the one billion people living in eastern China and the 800 million residents of sub-Saharan Africa will annually experience many hours of heat that surpass human tolerance.

These regions would primarily experience high-humidity heatwaves. Heatwaves with higher humidity can be more dangerous because the air cannot absorb excess moisture, which limits sweat evaporates from human bodies and moisture from some infrastructure, like evaporative coolers. Troublingly, researchers said, these regions are also in lower-to-middle income nations, so many of the affected people may not have access to air conditioning or any effective way to mitigate the negative health effects of the heat.

If warming of the planet continues to 3 C above pre-industrial levels, the researchers concluded, heat and humidity levels that surpass human tolerance would begin to affect the Eastern Seaboard and the middle of the United States -- from Florida to New York and from Houston to Chicago. South America and Australia would also experience extreme heat at that level of warming.

At current levels of heating, the researchers said, the United States will experience more heatwaves, but these heatwaves are not predicted to surpass human limits as often as in other regions of the world. Still, the researchers cautioned that these types of models often do not account for the worst, most unusual weather events.

"Models like these are good at predicting trends, but they do not predict specific events like the 2021 heatwave in Oregon that killed more than 700 people or London reaching 40 C last summer," said lead author Daniel Vecellio, a bioclimatologist who completed a postdoctoral fellowship at Penn State with Kenney. "And remember, heat levels then were all below the limits of human tolerance that we identified. So, even though the United States will escape some of the worst direct effects of this warming, we will see deadly and unbearable heat more often. And -- if temperatures continue to rise -- we will live in a world where crops are failing and millions or billions of people are trying to migrate because their native regions are uninhabitable."

Understanding human limits and future warming

Over the last several years, Kenney and his collaborators have conducted 462 separate experiments to document the combined levels of heat, humidity and physical exertion that humans can tolerate before their bodies can no longer maintain a stable core temperature.

"As people get warmer, they sweat, and more blood is pumped to their skin so that they can maintain their core temperatures by losing heat to the environment," Kenney said. "At certain levels of heat and humidity, these adjustments are no longer sufficient, and body core temperature begins to rise. This is not an immediate threat, but it does require some form of relief. If people do not find a way to cool down within hours, it can lead to heat exhaustion, heat stroke and strain on the cardiovascular system that can lead to heart attacks in vulnerable people."

In 2022, Kenney, Vecellio and their collaborators demonstrated that the limits of heat and humidity people can withstand are lower than were previously theorized.

"The data collected by Kenney's team at Penn State provided much needed empirical evidence about the human body's ability to tolerate heat. Those studies were the foundation of these new predictions about where climate change will create conditions that humans cannot tolerate for long," said co-author Matthew Huber, professor of earth, atmospheric and planetary sciences at Purdue University.

When this work was published, Huber, who had already begun work on mapping the impacts of climate change, contacted Vecellio about a potential collaboration. Huber had previously published widely cited work proposing a theoretical limit of humans' heat and humidity limits.

The researchers, along with Huber's graduate student, Qinqin Kong, decided to explore how people would be affected in different regions of the world if the planet warmed by between 1.5 C and 4 C. The researchers said that 3 C is the best estimate of how much the planet will warm by 2100 if no action is taken.

"Around the world, official strategies for adapting to the weather focus on temperature only," Kong said. "But this research shows that humid heat is going to be a much bigger threat than dry heat. Governments and policymakers need to re-evaluate the effectiveness of heat-mitigation strategies to invest in programs that will address the greatest dangers people will face."

Staying safe in the heat

Regardless of how much the planet warms, the researchers said that people should always be concerned about extreme heat and humidity -- even when they remain below the identified human limits. In preliminary studies of older populations, Kenney found that older adults experience heat stress and the associated health consequences at lower heat and humidity levels than young people.

"Heat is already the weather phenomenon that kills the most people in the United States," Vecellio, now a postdoctoral researcher at George Mason University's Virginia Climate Center, said. "People should care for themselves and their neighbors -- especially the elderly and sick -- when heatwaves hit."

The data used in this study examined the body's core temperatures, but the researchers said that during heatwaves, people experience health problems from other causes as well. For example, Kenney said that most of the 739 people who died during Chicago's 1995 heatwave were over 65 and experienced a combination of high body temperature and cardiovascular problems, leading to heart attacks and other cardiovascular causes of death.

Looking to the future

To stop temperatures from increasing, the researchers cite decades of research indicating that humans must reduce the emission of greenhouse gases, especially the carbon dioxide emitted by burning fossil fuels. If changes are not made, middle-income and low-income countries will suffer the most, Vecellio said.

As one example, the researchers pointed to Al Hudaydah, Yemen, a port city of more than 700,000 people on the Red Sea. Results of the study indicated that if the planet warms by 4 C, this city can expect more than 300 days when temperatures exceed the limits of human tolerance every year, making it almost uninhabitable.

"The worst heat stress will occur in regions that are not wealthy and that are expected to experience rapid population growth in the coming decades," Huber said. "This is true despite the fact that these nations generate far fewer greenhouse gas emissions than wealthy nations. As a result, billions of poor people will suffer, and many could die. But wealthy nations will suffer from this heat as well, and in this interconnected world, everyone can expect to be negatively affected in some way."

Read more at Science Daily

America's wealthiest 10% responsible for 40% of US greenhouse gas emissions

A new study, led by the University of Massachusetts Amherst, reveals that the wealthiest Americans, those whose income places them in the top 10% of earners, are responsible for 40% of the nation's total greenhouse gas emissions. The study, published in  PLOS Climate, is the first to link income, especially income derived from financial investments, to the emissions used in generating that income. The authors suggest that policymakers adopt taxes focused on shareholders and the carbon intensity of investment incomes in order to equitably meet the goal of keeping the global temperature to 1.5 C of warming.

Scientists and environmentalists have long known that consumption -- the amount and kind of food we eat, the vehicles we drive and all the stuff we buy -- is closely linked to greenhouse gas emission. Traditional environmental policy has then sought to either limit consumption or guide it into more environmentally friendly avenues: replacing red meat with plant-based diets or swapping a gas-guzzler for an electric vehicle.

"But," says Jared Starr, a sustainability scientist at UMass Amherst and the lead author of the new study, "consumption-based approaches to limiting greenhouse gas emissions are regressive. They disproportionately punish the poor while having little impact on the extremely wealthy, who tend to save and invest a large share of their income. Consumption-based approaches miss something important: carbon pollution generates income, but when that income is reinvested into stocks, rather than spent on necessities, it isn't subject to a consumption-based carbon tax."

"What happens," Starr asks, "when we focus on how emissions create income, rather than how they enable consumption?"

An answer to that seemingly simple question, however, is fraught with difficulty, because though it's relatively easy to capture a snapshot of wages and salaries -- the main sources of income for 90% of Americans -- it has been very difficult to get a sense of the investment income that makes up a large source of the richest Americans' wealth.

To solve this problem, Starr and his colleagues looked at 30 years' worth of data, drawing first on a database containing over 2.8 billion inter-sectoral financial transfers and following the flow of carbon and income through these transactions. This allowed them to calculate two different values: supplier-based and producer-based greenhouse gas emissions of income.

Supplier-based emissions are those created by industries that supply fossil fuels to the economy. For instance, the operational emissions released by fossil fuel companies are actually quite low, but they make enormous profits by selling oil to others who will burn it.

Producer-based emissions are those directly released by the operation of the business itself -- like a coal-fired power plant.

With these two figures in hand, Starr and his co-authors then linked their emissions data with another database containing detailed demographic and income data for over 5 million Americans. This database parses out income sources differentiating active income -- the wages or salaries earned through employment -- from the passively generated investment income.

Not only did the team find that over 40% of U.S. emissions were attributable with the income flows of the top 10%, they also discovered that the top 1% of earners alone generate 15 -- 17% of the nation's emissions. In general, white, non-Hispanic households had the highest emission-linked income and Black households the lowest. Emissions tended to increase with age, peaking with the 45-54 age group, before declining.

The team also identified "super emitters" with extremely high emissions intensity. These are almost exclusively among the top 0.1% of households, which are overrepresented in the fields of finance, real estate and insurance, manufacturing, and mining and quarrying.

"This research gives us insight into the way that income and investments obscure emissions responsibility," says Starr. "For example, 15 days of income for a top 0.1% household generates as much carbon pollution as a lifetime of income for a household in the bottom 10%. An income-based lens helps us focus in on exactly who is profiting the most from climate-changing carbon pollution, and design policies to shift their behavior."

In particular, Starr and his colleagues point to income and shareholder-based taxation -- rather than taxing consumables.

Read more at Science Daily

Sun 'umbrella' tethered to asteroid might help mitigate climate change

Earth is rapidly warming and scientists are developing a variety of approaches to reduce the effects of climate change. István Szapudi, an astronomer at the University of Hawaiʻi Institute for Astronomy, has proposed a novel approach -- a solar shield to reduce the amount of sunlight hitting Earth, combined with a tethered, captured asteroid as a counterweight. Engineering studies using this approach could start now to create a workable design that could mitigate climate change within decades.

The paper, "Solar radiation management with a tethered sun shield," is published in Proceedings of the National Academy of Sciences.

One of the simplest approaches to reducing the global temperature is to shade the Earth from a fraction of the Sun's light. This idea, called a solar shield, has been proposed before, but the large amount of weight needed to make a shield massive enough to balance gravitational forces and prevent solar radiation pressure from blowing it away makes even the lightest materials prohibitively expensive. Szapudi's creative solution consists of two innovations: a tethered counterweight instead of just a massive shield, resulting in making the total mass more than 100 times less, and the use of a captured asteroid as the counterweight to avoid launching most of the mass from Earth.

"In Hawaiʻi, many use an umbrella to block the sunlight as they walk about during the day. I was thinking, could we do the same for Earth and thereby mitigate the impending catastrophe of climate change?" Szapudi said.

Szapudi began with the goal of reducing solar radiation by 1.7%, an estimate of the amount needed to prevent a catastrophic rise in global temperatures. He found that placing a tethered counterbalance toward the Sun could reduce the weight of the shield and counterweight to approximately 3.5 million tons, about one hundred times lighter than previous estimates for an untethered shield.

While this number is still far beyond current launch capabilities, only 1% of the weight -- about 35,000 tons -- would be the shield itself, and that is the only part that needs to be launched from Earth. With newer, lighter materials, the mass of the shield can be reduced even further. The remaining 99% of the total mass would be asteroids or lunar dust used as a counterweight. Such a tethered structure would be faster and cheaper to build and deploy than other shield designs.

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Shrinking Arctic glaciers are unearthing a new source of methane

As the Arctic warms, shrinking glaciers are exposing bubbling groundwater springs which could provide an underestimated source of the potent greenhouse gas methane, finds new research published today in Nature Geoscience.

The study, led by researchers from the University of Cambridge and the University Centre in Svalbard, Norway, identified large stocks of methane gas leaking from groundwater springs unveiled by melting glaciers.

The research suggests that these methane emissions will likely increase as Arctic glaciers retreat and more springs are exposed. This, and other methane emissions from melting ice and frozen ground in the Arctic, could exacerbate global warming.

"These springs are a considerable, and potentially growing, source of methane emissions -- one that has been missing from our estimations of the global methane budget until now," said Gabrielle Kleber, lead author of the research who is from Cambridge's Department of Earth Sciences.

Scientists are concerned that additional methane emissions released by the Arctic thaw could ramp-up human-induced global warming. The springs the researchers studied hadn't previously been recognized as a potential source of methane emissions.

Kleber spent nearly three years monitoring the water chemistry of more than a hundred springs across Svalbard, where air temperatures are rising two times faster than the average for the Arctic. She likens Svalbard to the canary in the coal mine of global warming, "Since it is warming faster than the rest of the Arctic, we can get a preview of the potential methane release that could happen at a larger scale across this region."

Professor Andrew Hodson, study co-author from the University Centre in Svalbard said, "Living in Svalbard exposes you to the front-line of Arctic climate change. I can't think of anything more stark than the sight of methane outgassing in the immediate forefield of a retreating glacier."

Previously, research has centred on methane release from thawing permafrost (frozen ground). "While the focus is often on permafrost, this new finding tells us that there are other pathways for methane emissions which could be even more significant in the global methane budget," said study co-author Professor Alexandra Turchyn, also from Cambridge's Department of Earth Sciences.

Hodson added, "Until this work was conducted, we didn't understand the source and pathways of this gas because we were reading about studies from completely different parts of the Arctic where glaciers are absent."

The methane-delivering springs they identified are fed by a plumbing system hidden beneath most glaciers, which taps into large groundwater reserves within the underlying sediments and surrounding bedrock. Once the glaciers melt and retreat, springs appear where this groundwater network punches through to the surface.

The researchers found that methane emissions from glacial groundwater springs across Svalbard could exceed 2,000 tonnes over the course of a year -- which equates to roughly 10% of the methane emissions resulting from Norway's annual oil and gas energy industry.

This source of methane will likely become more significant as more springs are exposed, said Kleber, "If global warming continues unchecked then methane release from glacial groundwater springs will probably become more extensive."

Glacial groundwater springs aren't always easy to recognize, so Kleber trained her eye to pick them out from satellite images. Zooming in on the areas of land exposed by the retreat of 78 glaciers across Svalbard, Kleber looked for tell-tale blue trickles of ice where groundwater had leaked to the surface and frozen. She then travelled to each of these sites by snowmobile to take samples of the groundwater at locations where the ice had blistered due to pressurized water and gas build up.

When Kleber and the team profiled the chemistry of the water feeding these springs, they found that all bar one of the sites studied were highly concentrated with dissolved methane -- meaning that, when the spring water reaches the surface, there is plenty of excess methane that can escape to the atmosphere.

The researchers also identified localized hotspots of methane emissions, which were closely related to the type of rock from which the groundwater emerges. Certain rocks like shale and coal contain natural gases, including methane, produced by the breakdown of organic matter when the rocks formed. This methane can move upwards through fractures in the rock and into the groundwater.

"In Svalbard we are beginning to understand the complex and cascading feedbacks triggered by glacier melt -- it seems likely that there are more outcomes like this which we have yet to uncover," said Kleber.

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Preserving forests to protect deep soil from warming

A recent study led by scientists at Lawrence Berkeley National Laboratory (Berkeley Lab) and the University of Zurich has revealed that the organic compounds proposed for carbon sequestration in deep soil are highly vulnerable to decomposition under global warming.

The finding has implications for a key strategy in carbon management that relies on soil and forests -- natural carbon "sinks" -- to mitigate global warming.

About 25 percent of global carbon emissions are captured by forests, grasslands, and rangelands. During photosynthesis, plants store carbon in their cell walls and in the soil. Because of rich carbon stores from decades past, soils contain twice as much carbon as the atmosphere does, and deeper subsoils (more than 8 inches or 20 centimeters) account for roughly half of the soil carbon. But as global populations rise, so do our demands for new croplands and timber. Research shows that disturbing the natural world for commerce has a price: the United Nations' Intergovernmental Panel on Climate Change has warned that emissions from deforestation and agriculture account for around a fifth of global greenhouse gases.

"Our study shows that climate change will affect all aspects of soil carbon and nutrient cycling. It also shows that in terms of carbon sequestration, there's no silver bullet. If we want soil to sustain carbon sequestration in a warming world, we will need better soil management practices, which can mean minimal disturbance of soils during forest management and agriculture," said Margaret Torn, a senior scientist in Berkeley Lab's Earth & Environmental Sciences Area and a senior author of the study.

In 2021, Torn and her research team provided the first physical evidence that warmer temperatures lead to a significant drop in the carbon stocks stored in deep forest soils -- a loss of 33% over five years.

In the new study, Torn and first author Cyrill Zosso of the University of Zurich unveil a clearer picture of soil in a warming world. This time, the research team is the first to show that warmer temperatures lead to a significant drop in the soil organic carbon compounds that are created by plants during photosynthesis.

During an experiment at the University of California's Blodgett Forest Research Station in the foothills of California's Sierra Nevada mountains, the researchers used vertical heating rods to continuously warm 1-meter-deep (three-foot-deep) plots of soil by 4 degrees Celsius (7 degrees Fahrenheit). That is the amount of warming projected by the end of the 21st century if greenhouse gas emissions remain high.

They found that just 4.5 years of warming at this temperature led to large changes in carbon stocks at a depth of more than 30 centimeters (or approximately 12 inches) below the soil surface.

During spectroscopic experiments at the University of Zurich, Zosso identified the organic compounds that were affected by the warming.

The results were shocking: a 17% loss in lignin -- the compounds that give plants rigidity -- and a nearly 30% loss in cutin and suberin, the waxy compounds in leaves, stems, and roots that protect plants from pathogens.

Torn and Zosso were also surprised to find a significant difference in the amount of "pyrogenic carbon" in the soil samples that were artificially heated versus the ones that were not. Pyrogenic carbon is a type of soil organic carbon derived from charred vegetation and other organic matter remnants left in the wake of a wildfire.

Many researchers assume that pyrogenic carbon has the most potential to serve as a very stable form of sequestered carbon. "We found much less pyrogenic carbon in the deep soils when they were heated," Torn said.

"Pyrogenic carbon can stay in the soil for decades or even centuries, but we need to understand its vulnerability to warming or to changes in land management. Our study suggests that this material decomposed just as fast as anything else would when the soil was warmed," Torn explained. "This shows that when you put material deep into soil where it's in contact with minerals and microbes, those natural systems will decompose the material over time."

The researchers next plan to resample soil from the study to determine how nine years of warming impact soil composition and health. A new grassland warming experiment at the Point Reyes National Seashore in Northern California is also on the horizon. "We are also organizing all the world's deep-soil warming (or whole-soil warming) experiments to share data and know-how and conducting synthesis of the data to see what we can learn," Torn said.

Read more at Science Daily

Extremely hot days are warming twice as fast as average summer days in North-West Europe

New study analysed data on near-surface air temperatures recorded for North-West Europe over the past 60 years. The findings show that the maximum temperature of the hottest days is increasing at twice the rate of the maximum temperature of average summer days. The results highlight the need for urgent action by policy makers to adapt essential infrastructure to the impacts of climate change.

New research led by the University of Oxford has found that climate change is causing the hottest days in North-West Europe to warm at double the rate of average summer days. The difference in trends is most pronounced for England, Wales, and Northern France. Worryingly, while current climate models accurately predict the rate of warming for average days, they underestimate the rate at which the hottest days are warming compared to observations.

According to lead researcher Dr Matthew Patterson, from the University of Oxford's Department of Physics, the results indicate that extreme heat events -- such as the UK's record-breaking heatwave last summer -- are likely to become more regular. Dr Patterson said: 'These findings underline the fact that the UK and neighbouring countries are already experiencing the effects of climate change, and that last year's heatwave was not a fluke. Policy makers urgently need to adapt their infrastructure and health systems to cope with the impacts of higher temperatures.'

For the study, published today in Geographical Research Letters, Dr Patterson analysed data from the past 60 years (1960-2021) recording the maximum daily temperature, provided by the European Centre for Medium-Range Weather Forecasts.

Although the maximum recorded temperature varied between years, the overall trend clearly showed that the hottest days for North-West Europe had warmed at twice the rate of average summer days. For England and Wales, the average summer day increased by approximately 0.26°C per decade, whilst the hottest day increased by around 0.58°C per decade. However, this faster warming of the hottest days was not observed to this extent elsewhere in the Northern Hemisphere.

The reason causing this faster warming of the hottest days relative to average summer days is not yet understood. According to Dr Patterson, this may be due to the hottest summer days in North-West Europe often being linked to hot air transported north from over Spain. Because Spain is warming faster than North-West Europe, this means that air carried in from this region is ever more extreme relative to the ambient air in North-West Europe. The hottest days of 2022, for instance, were driven by a plume of hot air carried north from Spain and the Sahara. However, further research is needed to verify this.

Dr Patterson added: 'Understanding the warming rate of the hottest days will be important if we are to improve climate model simulation of extreme events and make accurate predictions about the future intensity of such events. If our models underestimate the rise in extreme temperatures over the coming decades, we will underestimate the impacts this will have.'

Extreme heat has significant negative impacts on many different aspects of society, including energy and transport infrastructure, and agriculture. It also exacerbates conditions including respiratory and cardiovascular diseases, putting a strain on health services.

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Wildfires in 2021 emitted a record-breaking amount of carbon dioxide

Carbon dioxide emissions from wildfires, which have been gradually increasing since 2000, spiked drastically to a record high in 2021, according to an international team of researchers led by Earth system scientists at the University of California, Irvine.

Nearly half a gigaton of carbon (or 1.76 billion tons of CO2) was released from burning boreal forests in North America and Eurasia in 2021, 150 percent higher than annual mean CO2 emissions between 2000 and 2020, the scientists reported in a paper in Science.

"According to our measurements, boreal fires in 2021 shattered previous records," said senior co-author Steven Davis, UCI professor of Earth system science. "These fires are two decades of rapid warming and extreme drought in Northern Canada and Siberia coming to roost, and unfortunately even this new record may not stand for long."

The researchers said that the worsening fires are part of a climate-fire feedback in which carbon dioxide emissions warm the planet, creating conditions that lead to more fires and more emissions.

"The escalation of wildfires in the boreal region is anticipated to accelerate the release of the large carbon storage in the permafrost soil layer, as well as contribute to the northward expansion of shrubs," said co-author Yang Chen, a UCI research scientist in Earth system science. "These factors could potentially lead to further warming and create a more favorable climate for the occurrence of wildfires."

Davis added, "Boreal fires released nearly twice as much CO2 as global aviation in 2021. If this scale of emissions from unmanaged lands becomes a new normal, stabilizing Earth's climate will be even more challenging than we thought."

Analyzing the amount of carbon dioxide released during wildfires is difficult for Earth system scientists for a variety of reasons. Rugged, smoke-enshrouded terrain hampers satellite observations during a combustion event, and space-based measurements are not at a sufficiently fine resolution to reveal details of CO2 emissions. Models used to simulate fuel load, fuel consumption and fire efficiency work well under ordinary circumstances but are not robust enough to represent extreme wildfires, according to the researchers.

And there is another roadblock of our own creation. "Earth's atmosphere already contains large amounts of carbon dioxide from human fossil fuel burning, and the existing greenhouse gas is difficult to distinguish from that produced by forest fires," said Chen.

The team found a way around these hurdles by studying carbon monoxide expelled into the atmosphere during blazes. Combining CO readings from MOPITT -- the Measurements Of Pollution In The Troposphere satellite instrument -- with existing fire emissions and wind speed datasets, the team reconstructed changes in global fire CO2 emissions from 2000-2021. Carbon monoxide has a shorter lifespan in the atmosphere than CO2, so if scientists detect an anomalous abundance of CO, that provides evidence of fires.

The researchers independently confirmed the occurrence of extreme fires in 2021 with data sets provided by NASA's Moderate Resolution Imaging Spectroradiometer aboard the Terra and Aqua satellites.

"The inversion approach employed in this study is a complementary method to the conventional bottom-up approach, which is based on estimating the burned area, fuel load, and combustion completeness," Chen said. "Combining these approaches can result in a more comprehensive understanding of wildfire patterns and their impacts."

The researchers said their data analysis revealed links between extensive boreal fires and climate drivers, especially increased annual mean temperatures and short-lived heat waves. They found that higher northern latitudes and areas with larger tree cover fractions were especially vulnerable.

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Wisconsin cave holds tantalizing clues to ancient climate changes, future shifts

Even in their dark isolation from the atmosphere above, caves can hold a rich archive of local climate conditions and how they've shifted over the eons. Formed over tens of thousands of years, speleothems -- rock formations unique to caves better known as stalagmites and stalactites -- hold secrets to the ancient environments from which they formed.

A newly published study of a stalagmite found in a cave in southern Wisconsin reveals previously undetected history of the local climate going back thousands of years. The new findings provide strong evidence that a series of massive and abrupt warming events that punctuated the most recent ice age likely enveloped vast swaths of the Northern Hemisphere.

The research, conducted by a team of scientists at the University of Wisconsin-Madison, appears March 2 in the journal Nature Geoscience. It's the first study to identify a possible link between ice age warm-ups recorded in the Greenland ice sheet -- known as Dansgaard-Oeschger events -- and climate records from deep within the interior of central North America.

"This is the only study in this area of the world that is recording these abrupt climate events during the last glacial period," says Cameron Batchelor, who led the analysis while completing her PhD at UW-Madison. Batchelor is now a postdoctoral fellow with the National Science Foundation working at the Massachusetts Institute of Technology.

The study is based on an exceptionally detailed chemical and physical analysis of a stalagmite that formed in the Cave of the Mounds, a tourist attraction and educational destination.

"At Cave of the Mounds our mission is to interpret this geologic wonder for our many annual visitors," says Joe Klimczak, general manager of the cave, which is a designated national natural landmark. "We are thrilled to deepen our understanding of the cave thanks to this world-class research and very exciting results."

The stalagmite Batchelor and her team analyzed grew extremely slowly -- taking roughly 20,000 years to reach the length of a human pinky finger.

The finger-length subterranean rock formed from a complex process that began in the sky. Water that originally fell as precipitation from the atmosphere soaked into the ground and percolated through soil and cracks in bedrock, dissolving tiny bits of limestone along the way. Some of that dissolved limestone was then left behind as countless drips of water fell from the ceiling of Cave of the Mounds, gradually accumulating into thousands of exceedingly thin layers of a mineral called calcite.

"And because those calcite layers are formed from that original precipitation, they're locking in the oxygen in the H2O originating from that precipitation," says Batchelor.

Therein lies the key to reconstructing an ancient climate record from a small, otherwise unremarkable rock. The oxygen trapped in the calcite exists in a couple varieties -- known as isotopes -- that scientists can use to glean information about the environmental conditions present during the precipitation events that formed it. That includes the temperature and possible sources of rain and snow that fell atop the Cave of the Mounds over thousands of years.

Batchelor's team used a specialized imaging technique that allowed them to identify layers within the stalagmite representing annual growth bands -- much like how tree rings record a season's worth of growth. Using another technique, they identified the isotopes in the tiny layers, revealing that present-day southern Wisconsin experienced a number of very large average temperature swings of up to 10 C (or about 18 F) between 48,000 and 68,000 years ago. Several of the temperature swings occurred over the course of around a decade.

While the dating information is not precise enough to definitively tie the temperature swings to the Dansgaard-Oeschger events recorded in Greenland ice cores, the researchers can say with confidence they occurred within similar timeframes. The team also performed climate simulations that bolstered the hypothesis that warming events occurred tens of thousands of years ago in the region of North America that includes present-day Wisconsin, and that the climate records from Cave of the Mounds and the Greenland ice sheet are indeed linked.

This potential link is exciting for Batchelor because it offers a climate story about central North America that has so far gone untold. Previous research from the mid-continent has not resolved signals of these large temperature swings, also called excursions.

"One theory was that the mid-continent is relatively immune to abrupt climate changes, and that maybe that's because it's surrounded by landmass, and there's some type of buffering happening," says Batchelor. "However, when we went and measured, we saw these really large excursions, and we were like, 'Oh, no, something is definitely happening.'"

That something -- a rapidly changing climate -- is unfolding yet again today, thanks to humans and our use of fossil fuels. Batchelor says she hopes her work in Wisconsin, and now a cave in the Canadian subarctic that she is studying for her postdoc, helps fill a big data gap about the history and potential future of abrupt climate changes in the mid-continent of North America.

Read more at Science Daily

The world will probably warm beyond the 1. 5-degree limit, but peak warming can be curbed

The world's current climate pledges are insufficient to keep the goal of the 2015 Paris Agreement firmly within grasp. Global warming will likely surpass the 1.5-degree Celsius limit. We are going to overshoot.

But countries can curb time spent in a warmer world by adopting more ambitious climate pledges and decarbonizing faster, according to new research led by scientists at the Department of Energy's Pacific Northwest National Laboratory, the University of Maryland and the U.S. Environmental Protection Agency. Doing so, they warn, is the only way to minimize the overshoot.

While exceeding the 1.5-degree limit appears inevitable, the researchers chart several potential courses in which the overshoot period is shortened, in some cases by decades. The study published today in the journal Nature Climate Change, during the 2022 United Nations Climate Change Conference, also known as COP27, held in Sharm El Sheikh, Egypt.

"Let's face it. We are going to breach the 1.5 degrees limit in the next couple of decades," said corresponding author and PNNL scientist Haewon McJeon. "That means we'll go up to 1.6 or 1.7 degrees or above, and we'll need to bring it back down to 1.5. But how fast we can bring it down is key."

Every second shaved off the overshoot translates to less time courting the most harmful consequences of global warming, from extreme weather to rising sea levels. Forgoing or delaying more ambitious goals could lead to "irreversible and adverse consequences for human and natural systems," said lead author Gokul Iyer, a scientist alongside McJeon at the Joint Global Change Research Institute, a partnership between PNNL and the University of Maryland.

"Moving fast means hitting net-zero pledges sooner, decarbonizing faster, and striking more ambitious emissions targets," said Iyer. "Every little bit helps, and you need a combination of all of it. But our results show that the most important thing is doing it early. Doing it now, really."

During COP26 in 2021, the same research team found that the then updated pledges could substantially increase the chance of limiting warming to 2 degrees Celsius over pre-industrial levels. In their new paper, the authors take an additional step in answering the question of how to move the needle from 2 to 1.5 degrees.

"The 2021 pledges don't add up to anywhere near 1.5 degrees -- we are forced to focus on the overshoot," said PNNL scientist Yang Ou, who co-led the study. "Here, we're trying to provide scientific support to help answer the question: What type of ratcheting mechanism would get us back down and below 1.5 degrees? That's the motivation behind this paper."

The Paths Forward

The authors model scenarios -- 27 emissions pathways in total, each ranging in ambition -- to explore what degree of warming would likely follow which course of action. At a base level, the authors assume that countries will meet their emissions pledges and long-term strategies on schedule.

In more ambitious scenarios, the authors model how much warming is limited when countries decarbonize faster and advance the dates of their net-zero pledges. Their results underscore the significance of "ratcheting near-term ambition," which entails rapid reductions in carbon dioxide emissions from all sectors of the energy system, immediately and through 2030.

If countries uphold their nationally determined contributions through 2030 and follow a two percent minimum decarbonization rate, for example, global carbon dioxide levels would not reach net zero this century.

Taking the most ambitious path outlined, however, could bring net-zero carbon dioxide emissions by 2057. Such a path, the authors write, is marked by "rapid transformations throughout the global energy system" and the scaling up of "low-carbon technologies like renewables, nuclear energy, as well as carbon capture and storage."

"The technologies that help us get to zero emissions include renewables, hydrogen, electric cars, and so on. Of course those are important players," said Iyer. "Another important piece of the puzzle is the technologies that can remove carbon dioxide from the atmosphere, like direct air capture or nature-based solutions."

The most ambitious scenarios outlined in their work are meant to be illustrative of the pathways on offer. But the central takeaway remains clear throughout all modeled scenarios: if 1.5 degrees is to be reattained sooner after we warm past it, more ambitious climate pledges must come.

Read more at Science Daily

Refreezing poles feasible and cheap, new study finds

The poles are warming several times faster than the global average, causing record smashing heatwaves that were reported earlier this year in both the Arctic and Antarctic. Melting ice and collapsing glaciers at high latitudes would accelerate sea level rise around the planet. Fortunately, refreezing the poles by reducing incoming sunlight would be both feasible and remarkably cheap, according to new research published today in IOP Publishing's Environmental Research Communications.

Scientists laid out a possible future program whereby high-flying jets would spray microscopic aerosol particles into the atmosphere at latitudes of 60 degrees north and south -- roughly Anchorage and the southern tip of Patagonia. If injected at a height of 43,000 feet (above airliner cruising altitudes), these aerosols would slowly drift poleward, slightly shading the surface beneath. "There is widespread and sensible trepidation about deploying aerosols to cool the planet," notes lead author Wake Smith, "but if the risk/benefit equation were to pay off anywhere, it would be at the poles."

Particle injections would be performed seasonally in the long days of the local spring and early summer. The same fleet of jets could service both hemispheres, ferrying to the opposite pole with the change of seasons.

Pre-existing military air-to-air refuelling tankers such as the aged KC-135 and the A330 MMRT don't have enough payload at the required altitudes, whereas newly designed high-altitude tankers would prove much more efficient. A fleet of roughly 125 such tankers could loft a payload sufficient to cool the regions poleward of 60°N/S by 2°C per year, which would return them close to their pre-industrial average temperatures. Costs are estimated at $11 billion annually -- less than one-third the cost of cooling the entire planet by the same 2°C magnitude and a tiny fraction of the cost of reaching net zero emissions.

"Game changing though this could be in a rapidly warming world, stratospheric aerosol injections merely treat a symptom of climate change but not the underlying disease. It's aspirin, not penicillin. It's not a substitute for decarbonization," says Smith.

Cooling at the poles would provide direct protection for only a small fraction of the planet, though the mid-latitudes should also experience some temperature reduction. Since less than 1% of the global human population lives in the target deployment zones, a polar deployment would entail much less direct risk to most of humanity than a global program. "Nonetheless, any intentional turning of the global thermostat would be of common interest to all of humanity and not merely the province of Arctic and Patagonian nations," adds Smith.

Read more at Science Daily

A prehistoric climate feedback loop

Against the backdrop of a rapidly warming planet, the need to better understand the nature and long-term impact of positive climatic feedback loops -- processes that accelerate the effects of warming -- becomes critically important.

One way to assess the role and impact of climatic feedback processes is to use modeling studies to look into the likely future based on what we know now. Climate projection models, for instance, are the tools behind the 1.5° C global warming threshold adopted by the Intergovernmental Panel on Climate Change.

Alternatively, you can look into the past to see what happened at a time when the Earth was up to 1-1.5°C warmer than today. That is what UC Santa Barbara's Syee Weldeab did in a paper published in the Proceedings of the National Academy of Sciences. The professor of paleoclimatology found feedback processes that have concerning implications for our modern, ongoing warming.

To get a paleoclimate perspective on global warming, Weldeab and his colleagues went back some 128,000 to 125,000 years ago to the peak Eemian warm episode. Oceans were up to 1-1.5°C warmer than during the Holocene (our current geological epoch). The authors examined marine sediment from the tropical Atlantic and found exceptionally strong warming of the intermediate water column during a brief interval within the peak Eemian warm episode.

"Remarkably, a substantially diminished Greenland Ice Sheet was capable of producing enough meltwater to perturb the density-driven circulation of the Atlantic Ocean," Weldeab said. "This contributed significantly to the large warming of the intermediate waters we reconstructed."

Typically, warm, salty water travels north from the tropics along the surface of the ocean and cools as it reaches northern mid and high latitudes. At this point, the now colder, denser water drops to the deep sea and travels back down toward the tropics. This interplay of density differences results in the currents that we're familiar with today.

"What happens when you put a large amount of fresh water into the North Atlantic is basically it disturbs ocean circulation and reduces the advection of cold water into the intermediate depth of the tropical Atlantic, and as a result warms the waters at this depth," he said.

While previous studies have discussed the disruption that meltwater caused to currents and temperatures at intermediate depths, the new paper reveals that this warming was "larger than previously thought."

"We show a hitherto undocumented and remarkably large warming of water at intermediate depths, exhibiting a temperature increase of 6.7°C from the average background value," Weldeab said.

This exceptionally strong warming has serious consequences. As the warm water impinges on marine sediment that contains abundant methane hydrates -- a mixture of frozen water and methane. These deposits are not far below the surface of the seafloor.

Weldeab explained that at high pressure and low temperatures, the introduction of unusually warm water heats the seafloor sediment, and the ice-encapsulated gases begin to dissolve, releasing methane. Weldeab and colleagues used carbon isotopes (13C/12C) in the shells of microorganisms to uncover the fingerprint of methane release and methane oxidation across the water column.

"This is one of several amplifying climatic feedback processes where a warming climate caused accelerated ice sheet melting," he said. "The meltwater weakened the ocean circulation and, as a consequence, the waters at intermediate depth warmed significantly, leading to destabilization of shallow subsurface methane hydrates and release of methane, a potent greenhouse gas."

It is not known for sure whether this feedback cycle will play out in the current round of global warming, though anthropogenic activity has created a higher rate of warming than the one that occurred in the Eemian period. These findings, according to the researchers, "document and connects a sequence of climatic events and climatic feedback processes associated with and triggered by the penultimate peak climate warming that can serve as a paleo-analogue for modern ongoing warming."

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Past events reveal how future warming could harm cold-water corals

How will future warming of the planet impact cold-water corals? A new analysis of ancient evidence from the last major global warming event identifies food and oxygen supply as key environmental factors that influence the vitality of cold-water corals in the North Atlantic Ocean and the Mediterranean Sea. Rodrigo da Costa Portilho-Ramos of the University of Bremen, Germany, and colleagues present these findings in the open-access journal PLOS Biology on May 19th.

Much like tropical corals in shallower waters, cold-water corals serve as crucial "engineers" of deep-sea reefs and mounds that are home to rich, unique ecosystems. As climate change progresses, researchers predict, cold-water corals are likely to face harm from such factors as rising ocean temperatures, decreased food supply, lower oxygen levels, and ocean acidification. However, no extinctions of cold-water coral ecosystems have been documented in real-time, so the precise factors that may determine their fate have been unclear.

To shed new light, Portilho-Ramos and colleagues turned to ancient evidence of past climate change as captured in seafloor sediments. They analyzed sediments collected at or near six sites of cold-water coral ecosystems in the North Atlantic Ocean and the Mediterranean Sea, applying standard techniques to reconstruct ocean conditions and the abundance of the common coral species Lophelia pertusa over the last 20,000 years. This period encompasses Earth's last major global warming event.

The analysis revealed that ancient L. pertusa abundance was most strongly influenced by changes in food supply, delivered either vertically from shallower depths or by lateral water flow along the seafloor. Low oxygen concentration also appeared to be a key stressor for L. pertusa. Meanwhile, changes in ocean temperature and salinity did not appear to be significantly associated with proliferation or disappearance of L. pertusa over time.

These findings suggest that climate change-driven alterations to ocean processes that affect food and oxygen supplies may play key roles in the future health of cold-water coral ecosystems. In some cases, the data suggest, high abundance of food may compensate for low oxygen levels.

Read more at Science Daily

Deep ocean warming as climate changes

Much of the "excess heat" stored in the subtropical North Atlantic is in the deep ocean (below 700m), new research suggests.

Oceans have absorbed about 90% of warming caused by humans. The study found that in the subtropical North Atlantic (25°N), 62% of the warming from 1850-2018 is held in the deep ocean.

The researchers -- from the University of Exeter and the University of Brest -- estimate that the deep ocean will warm by a further 0.2°C in the next 50 years.

Ocean warming can have a range of consequences including sea-level rise, changing ecosystems, currents and chemistry, and deoxygenation.

"As our planet warms, it's vital to understand how the excess heat taken up by the ocean is redistributed in the ocean interior all the way from the surface to the bottom, and it is important to take into account the deep ocean to assess the growth of Earth's 'energy imbalance'," said Dr Marie-José Messias, from the University of Exeter.

"As well as finding that the deep ocean is holding much of this excess heat, our research shows how ocean currents redistribute heat to different regions.

"We found that this redistribution was a key driver of warming in the North Atlantic."

The researchers studied the system of currents known as the Atlantic Meridional Overturning Circulation (AMOC).

AMOC works like a conveyer belt, carrying warm water from the tropics north -- where colder, dense water sinks into the deep ocean and spreads slowly south.

The findings highlight the importance of warming transferring by AMOC from one region to another.

Dr Messias said excess heat from the Southern Hemisphere oceans is becoming important in the North Atlantic -- now accounting for about a quarter of excess heat.

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Critical benefits of snowpack for winter wheat are diminishing

University of Minnesota scientists are partnering with a global team to study the complex effects of climate change on winter crops.

Warming winters may sound like a welcome change for some farmers because the change in temperature could reduce freezing stress on plants and create more ideal conditions for growing overwinter cash crops and winter cover crops. However, when looking at climate change from a cross-seasonal perspective and accounting for declining snowpack, researchers are finding that the whole picture isn't so sunny.

Reduced snow may result in more exposure of winter crops to freeze and could mean greater risks for agricultural drought.

In a new study published in Nature Climate Change, Zhenong Jin, Ph.D., an assistant professor in the Department of Bioproducts and Biosystems Engineering at the University of Minnesota, led an international team in researching the implications that could be associated with warmer winters and declining snowpack, using winter wheat (the largest winter crop in the U.S.) as an example.

"Although the implications of changes in snow for agricultural irrigation are beginning to be understood, the consequences of such for predominantly rainfed winter crops such as winter wheat remain largely unknown. There might be risks for being overoptimistic about growing overwinter crops under climate change," said Jin.

Researchers used panel regression, a powerful statistical method to analyze repeated observations over time, to attribute the interannual variability of winter wheat yield to multiple interactive environmental factors. These factors included cold season freezing degree days, growing degree days, rainfall and snowfall during the growing season and snow cover fraction during frozen days.

The researchers found:
 

• From 1999-2019, snow cover insulation weakened yield losses due to freezing stress by 22%.
• Projections show that future reduced snow cover could offset up to one-third of the yield benefit from reduced frost.

"Our study highlighted the potential freezing risk in winters with decreased snow cover, especially when seedlings were exposed to comparatively warmer conditions that caused loss of winter-hardiness, which can cause significant yield losses of winter crops," said Peng Zhu, Ph.D., a Researcher from the Climate and Environment Sciences Laboratory of the Pierre Simon Laplace Institute, who co-led this study.

This research will help inform breeders as they consider the complex tradeoffs among warming, reduced snowpack and occasional freezing threats when developing climate-smart cultivars.

These results also highlight the necessity of improving the representation of snow associated processes in crop models to better evaluate climate change effects and adaptation potential in cropping systems.

"It is worth noting that in some cropping systems freezing stress is appreciated, since it helps farmers control pests and diseases and snow is even removed or at least made more compact by farmers to increase the freezing of the soil," said Jin. "When data becomes available, future studies might also need to account for the influence of snow on pests and diseases to comprehensively understand what future changes in snowpack mean for the cropping system."

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New link between greenhouse gasses and sea level rise

A new study provides the first evidence that rising greenhouse gases have a long-term warming effect on the Amundsen Sea in West Antarctica. Scientists from British Antarctic Survey (BAS) say that while others have proposed this link, no one has been able to demonstrate it.

Ice loss from the West Antarctic Ice Sheet in the Amundsen Sea is one of the fastest growing and most concerning contributions to global sea level rise. If the West Antarctic Ice Sheet were to melt, global sea levels could rise by up to three metres. The patterns of ice loss suggest that the ocean may have been warming in the Amundsen Sea over the past one hundred years, but scientific observations of the region only began in 1994.

In the study -- published in the journal Geophysical Research Letters -- oceanographers used advanced computer modelling to simulate the response of the ocean to a range of possible changes in the atmosphere between 1920-2013.

The simulations show the Amundsen Sea generally became warmer over the century. This warming corresponds with simulated trends in wind patterns in the region which increase temperatures by driving warm water currents towards and beneath the ice. Rising greenhouse gases are known to make these wind patterns more likely, and so the trend in winds is thought to be caused in part by human activity.

This study supports theories that ocean temperatures in the Amundsen Sea have been rising since before records began. It also provides the missing link between ocean warming and wind trends which are known to be partly driven by greenhouse gasses. Ocean temperatures around the West Antarctic Ice Sheet will probably continue to rise if greenhouse gas emissions increase, with consequences for ice melt and global sea levels. These findings suggest, however, that this trend could be curbed if emissions are sufficiently reduced and wind patterns in the region are stabilised.

Dr Kaitlin Naughten, ocean-ice modeller at BAS and lead author of this study, says,

"Our simulations show how the Amundsen Sea responds to long-term trends in the atmosphere, specifically the Southern Hemisphere westerly winds. This raises concerns for the future because we know these winds are affected by greenhouse gases. However, it should also give us hope, because it shows that sea level rise is not out of our control."

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