Forecasters are predicting a “” this year. This will be the third winter in a row that the Pacific Ocean has been in a La Niña cycle, something that’s happened only twice before in records going back to 1950.

New research led by the 91̽�� offers a possible explanation. The , recently published in Geophysical Research Letters, suggests that climate change is, in the short term, favoring La Niñas.

“The Pacific Ocean naturally cycles between El Niño and La Niña conditions, but our work suggests that climate change could currently be weighing the dice toward La Niña,” said lead author , a 91̽��research scientist in atmospheric sciences. “At some point, we expect anthropogenic, or human-caused, influences to reverse these trends and give El Niño the upper hand.”

Scientists hope to predict the direction of these longer-term El Niño-like or La Niña-like climate trends in order to protect human life and property.

“This is an important question over the next century for regions that are strongly influenced by El Niño, which includes western North America, South America, East and Southeast Asia and Australia,” Wills said.

El Niño and La Niña events have , affecting patterns of rainfall, flooding and drought around the Pacific Rim. A winter tends to be cooler and wetter in the Pacific Northwest and hotter and drier in the U.S. Southwest. Other worldwide effects include drier conditions in East Africa, and rainier weather in Australia, Indonesia, Malaysia and the Philippines.

Knowing what to expect in the future helps communities prepare for potential weather in the coming season and in years to come.

Global warming is widely expected to favor El Niños. The reason is that the cold, deep water rising to the sea surface off South America will meet warmer air. Anyone who’s sweated knows that evaporation has a cooling effect, so the chillier ocean off South America, which has less evaporation, will warm faster than the warmer ocean off Asia. This decreases the temperature difference across the tropical Pacific and lightens the surface winds blowing toward Indonesia, the same as occurs during El Niño. Past climate records confirm that the climate was more El Niño-like during warmer periods.

But while Earth’s atmosphere has warmed in recent decades, the new study shows a surprising trend in the tropical ocean. The authors looked at temperatures at the surface of the ocean recorded by ship-based measurements and ocean buoys from 1979 to 2020. The Pacific Ocean off South America has actually cooled slightly, along with ocean regions farther south. Meanwhile, the western Pacific Ocean and nearby eastern Indian Ocean have warmed more than elsewhere. Neither phenomenon can be explained by the natural cycles simulated by climate models. This suggests that some process missing in current models could be responsible.

The upshot of these changes on either side of the tropical Pacific is that the temperature difference between the eastern and western Pacific has grown, surface winds blowing toward Indonesia have strengthened, and people are experiencing conditions typical of La Niña winters. The study focuses on temperature patterns at the ocean’s surface. Thirty years of data is too short to study the frequency of El Niño and La Niña events.

“The climate models are still getting reasonable answers for the average warming, but there’s something about the regional variation, the spatial pattern of warming in the tropical oceans, that is off,” Wills said.

The researchers aren’t sure why this pattern is happening. Their current work is exploring tropical climate processes and possible links to the ocean around Antarctica. Once they know what’s responsible, they may be able to predict when it will eventually switch to favor El Niños.

“If it turns out to be natural long-term cycles, maybe we can expect it to switch in the next five to 10 years, but if it is a long-term trend due to some processes that are not well represented in the climate models, then it would be longer. Some mechanisms have a switch that would happen over the next few decades, but others could be a century or longer,” Wills said.

The study was conducted before this year’s potential triple La Niña was announced. But Wills is cautious about declaring victory.

“These year-to-year changes are very unpredictable and it’s important not to get too hung up on any individual year — it doesn’t add a lot of statistical weight,” Wills said. “But I think it’s something that we should watch for in the next few years.”

Co-authors of the study are and at the UW; , a postdoctoral researcher at the Lamont-Doherty Earth Observatory who did the work as part of her 91̽��doctoral research; and at the University of Illinois at Urbana-Champaign. The study was funded by the National Science Foundation, the National Oceanic and Atmospheric Administration and the Alfred P. Sloan Foundation.

For more information, contact Wills at rcwills@uw.edu. Note: Wills is currently based in Colorado.

Record-breaking heat waves have occurred recently from Delhi to the Pacific Northwest, and the number of these deadly events is expected to increase. New research from the 91̽�� and Harvard University gives a range of heat impacts worldwide by the end of this century, depending on future emissions of greenhouse gases.

The was published Aug. 25 in the open-access journal Communications Earth & Environment.

“The record-breaking heat events of recent summers will become much more common in places like North America and Europe,” said lead author , who did the research as a doctoral student at the 91̽��and is now a postdoctoral researcher at Harvard. “For many places close to the equator, by 2100 more than half the year will be a challenge to work outside, even if we begin to curb emissions.”

“Our study shows a broad range of possible scenarios for 2100,” he added. “This shows that the emissions choices we make now still matter for creating a habitable future.”

The study looks at a combination of air temperature and humidity known as the “” that measures impact on the human body. A “dangerous” heat index is defined by the National Weather Service as 103 F (39.4 C). An “extremely dangerous” heat index is 124 F (51 C), deemed unsafe to humans for any amount of time.

“These standards were first created for people working indoors in places like boiler rooms — they were not thought of as conditions that would happen in outdoor, ambient environments. But we are seeing them now,” Vargas Zeppetello said.

The study finds that even if countries manage to meet the Paris Agreement goal of keeping warming to 2 C, crossing the “dangerous” threshold will be three to 10 times more common by 2100 in the U.S., Western Europe, China and Japan. In that same scenario, dangerous days could double by 2100 in the tropics, covering half the year.

In a worst-case scenario in which emissions remain unchecked until 2100, “extremely dangerous” conditions, in which humans should not be outdoors for any amount of time, could become common in countries closer to the equator — notably in India and sub-Saharan Africa.

“It’s extremely frightening to think what would happen if 30 to 40 days a year were exceeding the extremely dangerous threshold,” Vargas Zeppetello said. “These are frightening scenarios that we still have the capacity to prevent. This study shows you the abyss, but it also shows you that we have some agency to prevent these scenarios from happening.”

The study uses a probability-based method to calculate the range of future conditions. Instead of using the four future emissions pathways included in the Intergovernmental Panel on Climate Change reports, the authors use a statistical approach that combines historical data with population projections, economic growth and carbon intensity — the amount of carbon emitted for each dollar of economic activity — to predict the likely range of future CO2 concentrations.

The statistical approach “gives plausible ranges for carbon emissions and future temperature and has been estimated statistically from and validated against historical data,” said co-author , a 91̽��professor of statistics and of sociology with an adjunct appointment in atmospheric sciences.

The authors translated the higher carbon dioxide levels into a range of global temperature increases, then looked at how that would affect global monthly weather patterns.

“The number of days with dangerous levels of heat in the mid-latitudes — including the southeastern and central U.S. — will more than double by 2050,” said co-author , a professor of atmospheric sciences at the UW. “Even for the very low-end estimates of carbon emissions and climate response, by 2100 much of the tropics will experience ‘dangerous’ levels of heat stress for nearly half the year.”

The results underline the need to both reduce future greenhouse gas emissions and to protect populations, especially outdoor workers, against dangerous heat. The research was funded by the National Institutes of Health, the James S. McDonnell Foundation and the Tamaki Foundation.

For more information, contact Vargas Zeppetello at lzeppetello@fas.harvard.edu or Battisti at battisti@uw.edu.

Farmers struggling to adapt to rising temperatures in tropical regions can unleash the benefits of natural cooling, alongside a host of other wins, simply by dotting more trees across their pasturelands. For the first time, a study led by the 91̽�� puts tangible numbers to the cooling effects of this practice.

Researchers at the 91̽��and The Nature Conservancy, along with Duke University, the University of California San Diego and Stony Brook University Hospital, find that adding trees to pastureland, technically known as , can cool local temperatures by up to 2.4 C (4.3 F) for every 10 metric tons of woody material added per hectare (about 4 tons per acre) depending on the density of trees, while also delivering a range of other benefits for humans and wildlife.

The was published Feb. 4 in Nature Communications.

“The way in which lands are used has implications for human health and safety,” said first author , who did this work as a 91̽��doctoral student in atmospheric sciences. “Our past studies demonstrated how deforestation can increase local temperatures to unsafe levels. Here, we show that planting additional trees on low-latitude pasturelands can provide substantial cooling benefits, highlighting one pathway for adding further resilience to the rising heat being experienced in these settings.”

The researchers analyzed satellite data from 2018 to compare the annual average temperature at each location across the American and African tropics with an existing data set of bare pastureland and pastureland with different amounts of tree cover, in order to quantify the local cooling effect of the trees.

Using projections for rising global temperatures for the year 2050, the authors then identified where rural communities could gain most from practicing silvopasture in the future. The authors note that the cooling effect works on all spatial scales — even smallholder farmers could access these cooling benefits, they said, by intensifying tree-planting on their own pasturelands.

“We already have plenty of peer-reviewed evidence for the multiple socioeconomic and ecological benefits agroforestry systems like silvopasture can provide — from increased food security and farmer incomes, to greater biodiversity and better access to traditional (and affordable) medicines in remote rural communities,” said corresponding author , a senior scientist at The Nature Conservancy.

“Adding our findings on the localized cooling potential of silvopasture to the mix only serves to underline the huge spectrum of advantages that come from trees in pastureland, ultimately benefiting not only vulnerable rural communities in tropical hotspots, but people and wildlife in general.”

Several of this study’s co-authors also collaborated on another recent paper that revealed the extent to which localized temperature rises, driven by a deadly combination of global warming and tropical deforestation, are making outdoor work increasingly perilous for vulnerable communities across the tropics.

Other co-authors are and Dr. at the UW; , who did the work at the 91̽��and is now at Duke University; Susan Cook-Patton, Nicholas Wolff and Timm Kroeger at TNC; Joseph Bettles at the University of California, San Diego; and Dr. Arjun Balakumar at Stony Brook University Hospital. Vargas Zeppetello is now a postdoctoral researcher at Harvard University.

The research was funded by The Nature Conservancy, the Bezos Earth Fund, the Tamaki Foundation, the government of Norway and NASA.

For more information, contact Vargas Zeppetello at lvz7@uw.edu  In the TNC press office, contact Ciaran Clayton, ciaran.clayton@tnc.org (U.S.) and Tom Jennings, tom.jennings@tnc.org (U.K./Europe).

This article was adapted from a The Nature Conservancy .

Outdoor workers in the world’s lower-latitude tropical forests may face a greater risk of heat-related deaths and unsafe working conditions because of deforestation and climate warming, according to a led by The Nature Conservancy, the 91̽�� and Indonesia’s Mulawarman University.

In the study, researchers found that increased temperatures of 0.95 C (1.7 F) in the deforested areas of Berau Regency, Indonesia, between 2002 and 2018 were linked to roughly 118 additional deaths in 2018, and 20 additional minutes of daily conditions too hot for humans to work in safely. Future climate warming of 2 C (3.6 F) above 2018’s levels could increase deaths in Berau by 20% (approximately 282 additional annual deaths) and another five unsafe work hours per day — even without greater deforestation.

“Ambient heat exposure and internal body heat from heavy physical work can increase the risk of heat-related illnesses, including heat exhaustion and heat stroke — which can be fatal — as well as acute kidney injury and traumatic injuries,” said  co-author , associate professor and assistant chair of environmental and occupational health sciences in the 91̽��School of Public Health.

Researchers point out that the increase in heat-related deaths with a 2 C rise in global temperatures would be comparable to mortality from other long-term public health challenges in Asia, such as tobacco smoking. In addition, they write, “workers in Berau are already adapting to hotter temperatures due to deforestation, suggesting those engaged in outdoor work may already be approaching their adaptive capacity through behavioral adaptations.”

The study in Lancet Planetary Health used publicly available and secondary data such as satellite monitoring of forest cover, temperatures, climate models, population densities, and the report published annually in The Lancet by the 91̽��Institute for Health Metrics and Evaluation. Researchers focused on Berau as an area emblematic of tropical forest regions facing rapid deforestation.

“Approximately 800 million people live and work in the world’s tropical forest nations,” Spector said. “These forests can act as natural air conditioners and sequester carbon, thus having implications for both climate change adaptation and mitigation. Information from this modeling study should be considered in discussions about trade-offs between economic welfare, human health, the natural environment and decisions about climate change adaptation and mitigation.”

Other 91̽��authors of the study are , graduate student, and , professor and Tamaki Endowed Chair, in the Department of Atmospheric Science; and , professor of global health and environmental and occupational health sciences in the School of Public Health. For complete list of authors and more about the study see The Nature Conservancy’s .

The study was supported by a pilot research grant from the 91̽��Population Health Initiative.

Four 91̽�� faculty members are among the leaders in academia, business, philanthropy, the humanities and the arts of the , one of the nation’s oldest and most prestigious honorary societies.

The 91̽��fellows are , professor emeritus of education; , professor of atmospheric sciences; , professor of biology; and , professor emeritus of Asian languages and literature. They are among .

“We are honoring the excellence of these individuals, celebrating what they have achieved so far, and imagining what they will continue to accomplish,” said David Oxtoby, president of the academy. “The past year has been replete with evidence of how things can get worse; this is an opportunity to illuminate the importance of art, ideas, knowledge and leadership that can make a better world.”

Honored for his work in education,  is the founding director of the Banks Center for Educational Justice – originally the Center for Multicultural Education – in the 91̽��College of Education. He holds the Kerry and Linda Killinger Endowed Chair in Diversity Studies Emeritus and retired from the UW in 2019, after 50 years.

Widely known as the “father of multicultural education,” Banks specializes in the teaching of social studies, diversity and citizenship education. Banks has written and edited numerous articles and books, including “The Handbook of Research in Multicultural Education,” “The Encyclopedia of Diversity in Education” and the70-plus-volume Multicultural Education Series of books published by Teachers College Press at Columbia University.  Most recently, a collection of his works was published, “Diversity, Transformative Knowledge and Civic Education: Selected Essays.” Banks is a member of the National Academy of Education and a Fellow of the American Educational Research Association.

The Banks Center, established in 1992, is devoted to cultivating partnerships, and developing programs and collaborative research from early childhood through higher education.

, a 91̽��professor of atmospheric sciences who holds the Tamaki Endowed Chair, is recognized for his work on climate variability. Battisti earned his doctorate in atmospheric sciences at the 91̽��in 1988, then went to the University of Wisconsin before returning to the 91̽��as a faculty member in 1990.

Battisti’s research looks at how interactions between the ocean, air, land and sea ice can affect the climate on timescales from seasons to decades. His more recent research has looked at how climate change is likely to affect global food production. Battisti directed the Joint Institute for the Study of the Atmosphere and Ocean, a partnership between the 91̽��and NOAA, from 1997 to 2003, and co-chaired the science steering committee for the U.S. program from 1998 to 2002. He is also a fellow of the American Meteorological Society and of the American Geophysical Union.

, a professor of biology and director of the , earned a doctoral degree in zoology from the Ohio State University in 1974 and joined the 91̽��faculty later that year. She has studied the health, behavior and ecological dynamics of South American penguins for nearly four decades — particularly Magellanic penguins in Argentina and Galápagos penguins in Ecuador.

Boersma advocates for penguins as indicators of ocean health. Her research on Galápagos penguins has focused on their adaptations to El Niño and other events in this “predictably unpredictable” region. Recent Magellanic penguin studies seek to understand how conditions in the ocean — where they feed outside of the breeding season — impact their health, well-being and reproductive success.

Over the years, Boersma has worked with partners such as the Global Penguin Society to protect Magellanic nesting grounds and welcome thousands of ecotourists to view the penguins. She holds the Wadsworth Endowed Chair in Conservation Science at the 91̽��and has thrice been a finalist for the Indianapolis Prize, the highest honor for animal conservation.

is professor emeritus of Asian languages and literature and the William P. and Ruth Gerberding university professor emeritus. He was recognized for his contributions to religious studies. He is the former president of the International Association of Buddhist Studies and of the American Oriental Society, and since 1996 the director of the UW’s Early Buddhist Manuscripts Project, which is charged with the study and publication of the oldest surviving Buddhist manuscripts, dating back to the first century BCE. Salomon earned his doctorate in Sanskrit from the University of Pennsylvania in 1975 and joined the 91̽��in 1981.

Salomon is a leading figure in the field of early Buddhist studies. His specialties include Sanskrit language and literature, Indian Buddhist literature and textual studies, Indian epigraphy and paleography, Gāndhārī language and Gandhāran studies, and the world history of writing. He has published seven books and over 150 articles in these and other fields.

The Academy was established in 1780 to provide guidance to a young nation that would face challenges and need expertise and excellence to emerge stronger. Its founders, including John Adams and John Hancock, believed the new republic should honor exceptionally accomplished individuals and engage them in advancing the public good. The Academy’s dual mission remains essentially the same today with members from increasingly diverse fields working together to share ideas and recommendations in the arts, democracy, education, global affairs and science.

Research led by the 91̽�� looks at what climate change will mean for global yields of this crop. The results show that warmer temperatures by the end of this century will reduce yields throughout the world, confirming previous research. But the study also shows dramatic increases in the variability of corn yields from one year to the next and the likelihood of simultaneous low yields across multiple high-producing regions, which could lead to price hikes and global shortages.

The study was published the week of June 11 in the .

“Previous studies have often focused on just climate and plants, but here we look at climate, food and international markets,” said lead author , a 91̽��postdoctoral researcher in atmospheric sciences. “We find that as the planet warms, it becomes more likely for different countries to simultaneously experience major crop losses, which has big implications for food prices and food security.”

In the wake of a recent 91̽��study looking at the under climate change, this study addressed overall yields and price volatility of corn.

While most rice is used domestically, corn is traded on international markets. Four countries — U.S., Brazil, Argentina and the Ukraine — account for 87 percent of the global corn exports (China mostly produces for domestic use). Today the probability that all four exporters would have a bad year together, with yields at least 10 percent below normal, is virtually zero.

But results show that under 2 degrees Celsius warming, which is projected if we succeed in curbing greenhouse gas emissions, this risk increases to 7 percent. Under 4 degrees Celsius warming, which the world is on track to reach by the end of the century if current greenhouse gas emissions rates continue, there’s an 86 percent chance that all four maize-exporting countries would simultaneously suffer a bad year.

In other words, it suggests cases like the , which devastated crops there, will be more likely to coincide with bad years in other regions.

“Yield variability is important for determining food prices in international markets, which in turn has big implications for food security and the ability of poor consumers to buy food,” Tigchelaar said.

The study used global climate projections with maize growth models to confirm previous research showing that warmer temperatures will negatively affect corn crops.

“When people think about climate change and food, they often initially think about drought,” Tigchelaar said, “but it’s really extreme heat that’s very detrimental for crops. Part of that is because plants grown at a higher temperature demand more water, but it’s also that extreme heat itself negatively affects crucial stages in plant development, starting with the flowering stage and ending with the grain-filling stage.”

The results show that while warmer temperatures will severely decrease average maize yields in the southeastern U.S., Eastern Europe and sub-Saharan Africa, and will increase the variability in the U.S. and other exporting nations.

“Even with optimistic scenarios for reduced emissions of greenhouse gases, results show that the volatility in year-to-year maize production in the U.S. will double by the middle of this century, due to increasing average growing season temperature,” said co-author , a 91̽��professor of atmospheric sciences. “The same will be true in the other major maize-exporting countries. Climate change will cause unprecedented volatility in the price of maize, domestically and internationally.”

The study did not include precipitation changes, since those are harder to predict, and projections show that changes will be small compared to the natural changes in rainfall from one year to the next. It also assumed that temperature swings will stay the same as today, though some models project temperatures will become more variable under climate change.

“We took a conservative approach and assumed the ‘weather’ will be the same, only acting on top of an overall warmer climate,” Battisti said.

The findings support efforts to pursue new agricultural technology to ensure food security for a growing global population. The authors write that their results “underscore the urgency of investments in breeding for heat tolerance.”

The other co-authors are Rosamond Naylor at Stanford University and Deepak Ray at the University of Minnesota. The study was funded by the Tamaki Foundation.

###

For more information, contact Tigchelaar at mtigch@uw.edu or Battisti at battisti@uw.edu.

A finds that a substantial chunk of summer sea ice loss in recent decades was due to natural variability in the atmosphere over the Arctic Ocean. The study, from the 91̽��, the University of California Santa Barbara and federal scientists, is published March 13 in Nature Climate Change.

“Anthropogenic forcing is still dominant — it’s still the key player,” said first author , a climate scientist at the University of California Santa Barbara who holds an affiliate position at the UW, where he began the work as a research scientist in the UW’s Applied Physics Laboratory. “But we found that natural variability has helped to accelerate this melting, especially over the past 20 years.”

The paper builds on previous work by Ding and other 91̽��scientists that found changes in the tropical Pacific Ocean have in recent decades that has boosted warming in that region.

The hot spot is a large region of higher pressure where air is squeezed together so it becomes warmer and can hold more moisture, both of which bring more heat to the sea ice below. The new paper focuses specifically on what this atmospheric circulation means for Arctic sea ice in September, when the ocean reaches its maximum area of open water.

“The idea that natural or internal variability has contributed substantially to the Arctic sea ice loss is not entirely new,” said second author , a 91̽�� polar scientist who tracks Arctic sea ice. “This study provides the mechanism, and uses a new approach to illuminate the processes that are responsible for these changes.”

Ding designed a new sea ice model experiment that combines forcing due to climate change with observed weather in recent decades. The model shows that a shift in wind patterns is responsible for about 60 percent of sea ice loss in the Arctic Ocean since 1979. Some of this shift is related to climate change, but the study finds that 30-50 percent of the observed sea ice loss since 1979 is due to natural variations in this large-scale atmospheric pattern.

“What we’ve found is that a good fraction of the decrease in September sea ice melt in the past several decades is most likely natural variability. That’s not really a surprise,” said co-author , a 91̽��professor of atmospheric sciences.

“The method is really innovative, and it nails down how much of the observed sea ice trend we’ve seen in recent decades in the Arctic is due to natural variability and how much is due to greenhouse gases.”

The long-term natural variability is ultimately thought to be driven by the tropical Pacific Ocean. Conditions in the tropical Pacific set off ripple effects, and atmospheric waves snake around the globe to create areas of higher and lower air pressure.

Teasing apart the natural and human-caused parts of sea ice decline will help to predict future sea ice conditions in Arctic summer. Forecasting sea ice conditions is relevant for shipping, climate science, Arctic biology and even tourism. It also helps to understand why sea ice declines may be faster in some decades than others.

“In the long term, say 50 to 100 years, the natural internal variability will be overwhelmed by increasing greenhouse gases,” Ding said. “But to predict what will happen in the next few decades, we need to understand both parts.”

What will happen next is unknown. The tropical Pacific Ocean could stay in its current phase or it could enter an opposite phase, causing a low-pressure center to develop over Arctic seas that would temporarily slow the long-term loss of sea ice due to increased greenhouse gases.

“We are a long way from having skill in predicting natural variability on decadal time scales,” Ding said.

The research was funded by NOAA, the National Science Foundation, NASA and the Tamaki Foundation. Other co-authors are Stephen Po-Chedley, Edward Blanchard-Wrigglesworth and Ryan Eastman in the UW’s Department of Atmospheric Sciences; Eric Steig in the UW’s Department of Earth and Space Sciences; and Michelle L’Heureux, Kristin Harnos and Qin Zhang at the National Oceanographic and Atmospheric Administration’s Climate Prediction Center.

###

For more information, contact Ding at qinghua@ucsb.edu, Schweiger at 206-543-1312 or axel@apl.uw.edu and Battisti at 206-543-2019 or battisti@uw.edu.

NOAA: NA15OAR4310162; NSF: ARC-1203425; NASA: NNXBAQ35G

A new from the 91̽�� and the Massachusetts Institute of Technology hopes to complete the understanding of what happens to the planet under climate change. Instead of carbon dioxide, or CO2, creating a blanket to slowly warm the planet, a paper this week in the shows the story is a little more complicated – though the ending is, unfortunately, the same.

“This is a neat study in that it changes the way we think about the climate system,” said lead author , a postdoctoral researcher at MIT who is now beginning as a research associate at the UW’s . “We looked at processes that are well captured in the models, but the conceptual understanding of how they work hasn’t been fleshed out before.”

When CO2 is first added, it does act as a blanket, trapping long-wave infrared energy coming off the Earth. The atmosphere then emits less of this long-wave radiation to space because the upper atmosphere is cooler than the Earth’s surface, just as the top of your blanket is cooler than your body. But the Earth gradually heats up under this blanket, and hotter objects emit more long-wave radiation, so within about a decade the effect of adding the thicker blanket has been canceled by the warmer body emitting more energy.

So what keeps the planet warming after the first decade? In the longer term, the study shows that the Earth begins to absorb more shortwave radiation – the high-energy rays coming directly from the sun.

Previously people had shied away from talking about shortwave radiation because clouds can reflect this visible light back to space, and clouds remain one of the big unknowns under climate change.

Regardless of what happens to clouds, these researchers say, the planet is likely to have less ice and the air will become more humid under climate change, both of which will act to absorb more shortwave radiation from the sun. Those effects will be like putting tanning oil on the planet, letting it absorb more of the sun’s incoming rays.

Melting ice creates darker surfaces that can absorb more heat, and the more melting the more heat it can absorb. Likewise, warmer air holds more water vapor, causing it to absorb solar radiation that might otherwise bounce back off clouds, ice or snow.

“While greenhouse gases trap one type of radiation, it’s the other type – visible, shortwave radiation – that is really sustaining global warming over the long term,” said co-author , a postdoctoral researcher at MIT who will join the 91̽��faculty this fall with a joint appointment in oceanography and atmospheric sciences.

The result could help people better conceptualize global warming. It could also help better detect climate change in satellite data, which can measure both shortwave radiation reflected by the Earth and long-wave radiation emitted by the Earth.

Most of the study’s simulations involved a one-time addition of carbon dioxide into the atmosphere. One scenario simulated continuously increasing CO2, as is happening now – in that case, the long-wave radiation effect lasted about 20 years before the shortwave effect took over.

“Our results do not change our overall expectation that the planet will continue to warm due to the burning of fossil fuels, but they do change our fundamental understanding of how that warming comes about,” said co-author , a 91̽��professor of atmospheric sciences.

The study supports what scientists are seeing in models and observations, Battisti added.

Donohoe and Armour began the research as 91̽��graduate students along with co-author , now a postdoctoral researcher at the National Center for Atmospheric Research in Boulder.

The research was funded by the National Science Foundation, the National Oceanic and Atmospheric Administration and the James S. McDonnell Foundation.

###

For more information, contact Donohoe at thedhoe@mit.edu, or Armour at karmour@mit.edu.

NSF grant: AGS-0960497

, a 91̽��professor of atmospheric sciences, was recognized for his work on climate variability. Battisti earned his doctorate in atmospheric sciences at the 91̽��in 1988, then went to the University of Wisconsin before returning to the 91̽��as a faculty member in 1990.

Battisti’s research looks at how interactions between the ocean, air, land and sea ice can affect the climate on timescales from seasons to decades. His more recent research has looked at how climate change is likely to affect global food production. Battisti directed the UW-based from 1997 to 2003, and co-chaired the science steering committee for the U.S. program from 1998 to 2002. He is a fellow of the American Meteorological Society and has twice received distinguished teaching awards.

, a 91̽��professor of atmospheric sciences, was elected for his work on atmospheric radiation and climate change. Fu earned his doctorate at the University of Utah in 1991 and was on the faculty at Canada’s Dalhousie University before joining the 91̽��in 2000.

Fu’s research concerns how the atmosphere and clouds interact with sunlight, and how satellites measure Earth variables. His work on tropospheric temperature trends from satellite observations established in the atmosphere and at Earth’s surface. He also discovered a shift toward the poles of subtropical jets in a warming climate, indicating a widening of the tropics. Fu is a fellow of the American Meteorological Society and holds an affiliate faculty position at China’s Lanzhou University.

Also elected this year was , a 91̽��affiliate professor of oceanography and scientist at the National Oceanic and Atmospheric Administration in Seattle. His research concerns ocean circulation near the equator, the frequency of extreme El Niños under greenhouse warming, and the connection between winds and climate change.

###

Now 91̽�� atmospheric scientists have estimated that up to half of the recent warming in Greenland and surrounding areas may be due to climate variations that originate in the tropical Pacific and are not connected with the overall warming of the planet. Still, at least half the warming remains attributable to global warming caused by rising carbon dioxide emissions. The is published May 8 in .

Greenland and parts of neighboring Canada have experienced some of the most extreme warming since 1979, at a rate of about 1 degree Celsius per decade, or several times the global average.

“We need to understand why in the last 30 years global warming is not uniform,” said first author , a 91̽��research scientist in atmospheric sciences. “Superimposed on this global average warming are some regional features that need to be explained.”

The study used observations and advanced computer models to show that a warmer western tropical Pacific Ocean has caused atmospheric changes over the North Atlantic that have warmed the surface by about a half-degree per decade since 1979.

“The pattern of the changes in the tropical Pacific that are responsible for remarkable atmospheric circulation changes and warming in Greenland and the Canadian Arctic are consistent with what we would call natural variability,” said co-author , a 91̽��professor of atmospheric sciences.

Researchers say it’s not surprising to find the imprint of natural variability in an area famous for its melting ice. In many of the fastest-warming areas on Earth, global warming and natural variations both contribute to create a “perfect storm” for warming, said co-author , a 91̽��professor of atmospheric sciences.

The natural variations in the new study related to an unusually warm western tropical Pacific, near Papua New Guinea. Since the mid-1990s the water surface there has been about 0.3 degrees hotter than normal. Computer models show this affects the regional air pressure, setting off a stationary wave in the atmosphere that arcs in a great circle from the tropical Pacific toward Greenland before turning back over the Atlantic.

“Along this wave train there are warm spots where the air has been pushed down, and cold spots where the air has been pulled up,” Wallace said. “And Greenland is in one of the warm spots.”

In previous studies, Wallace and Battisti have documented the existence of decades-long climate variations in the Pacific Ocean that resemble the well-known shorter-range El Niño variations.

This particular location in the tropical Pacific may be a sweet spot for generating global atmospheric waves. A series of led by co-author , a 91̽��professor of Earth and space sciences, working with Ding and Battisti, showed that waves starting in the same place but radiating southward are warming West Antarctica and melting the Pine Island Glacier.

Researchers can’t say for how long the tropical Pacific will remain in this state.

“Our work shows that about half of the warming signal in Greenland comes from the predictable part – forcing of climate by anthropogenic greenhouse gases – but about half comes from the unpredictable part,” Steig said.

This makes shorter-term forecasts difficult, but helps scientists to make more accurate long-range projections.

“Nothing we have found challenges the idea that globally, glaciers are retreating,” Battisti said. “We looked at this place because the warming there is really remarkable. Our findings help us to understand on a regional scale how much of what you see is human-induced by the buildup of CO2, and how much of it is natural variability.”

The dramatic message of “Chasing Ice” remains true, authors say.

“There’s nothing in this paper that negates the message in the movie,” Wallace said. “Ice appears to be exquisitely sensitive to the buildup of greenhouse gases, more than we ever would have thought.” Natural variations could either accelerate or decelerate the melting rate of Greenland’s glaciers in coming decades, he said, but “in the long run, the human-induced component is likely to prevail.”

The research was funded by the National Science Foundation, UW’s Quaternary Research Center, the National Basic Research Program of China and the APEC Climate Center. Other co-authors are at the UW; Ailie Gallant at Australia’s Monash University; and Hyung-Jin Kim at South Korea’s APEC Climate Center.

###

For more information, contact Ding at qinghua@uw.edu, Wallace at 206-543-7390 or wallace@atmos.washington.edu, Battisti at 206-543-2019 or battisti@uw.edu, and Steig at 206-685-3715 or steig@uw.edu.

NSF grant numbers: OPP 1043092, ATM 1122989.