Clouds come in myriad shapes, sizes and types, which control their effects on climate. New research led by the 91Ě˝»¨ shows that splintering of frozen liquid droplets to form ice shards inside Southern Ocean clouds dramatically affects the clouds’ ability to reflect sunlight back to space.

The , published March 4 in the open-access journal AGU Advances, shows that including this ice-splintering process improves the ability of high-resolution global models to simulate clouds over the Southern Ocean – and thus the models’ ability to simulate Earth’s climate.

“Southern Ocean low clouds shouldn’t be treated as liquid clouds,” said lead author , a 91Ě˝»¨doctoral student in atmospheric sciences. “Ice formation in Southern Ocean low clouds has a substantial effect on the cloud properties and needs to be accounted for in global models.”

Results show that it’s important to include the process whereby icy particles collide with supercooled droplets of water causing them to freeze and then shatter, forming many more shards of ice. Doing so makes the clouds dimmer, or decreases their reflectance, allowing more sunlight to reach the ocean’s surface.

The difference between including the details of ice formation inside the clouds versus not including them was 10 Watts per square meter between 45 degrees south and 65 degrees south in the summer, which is enough energy to have a significant effect on temperature.

The study used observations from a 2018 field campaign that flew through Southern Ocean clouds, as well as data from NASA’s CERES satellite and the Japanese satellite .

Ice formation reduces clouds’ reflectance because the ice particles form, grow and fall out of the cloud very efficiently.

“The ice crystals deplete much of the thinner cloud entirely, therefore reducing the horizontal coverage,” Atlas said. “Ice crystals also deplete some of the liquid in the thick cores of the cloud. So the ice particles both reduce the cloud cover and dim the remaining cloud.”

In February, which is summer in the Southern Ocean, about 90% of the skies are covered with clouds, and at least 25% of those clouds are affected by the type of ice formation that was the focus of the study. Getting clouds right, especially in the new models that use smaller grid spacing to include clouds and storms, is important for calculating how much solar radiation reaches Earth.

“The Southern Ocean is a massive global heat sink, but its ability to take heat from the atmosphere depends on the temperature structure of the upper ocean, which relates to the cloud cover,” Atlas said.

Co-authors of the study are , a 91Ě˝»¨professor emeritus of atmospheric sciences now at the Allen Institute for AI in Seattle; at Stony Brook University in New York; and , a 91Ě˝»¨research scientist in atmospheric sciences. The research was funded by the National Science Foundation.

For more information contact Atlas at ratlas@uw.edu.

NSF grants: GS-1660604, AGS-1660609, OISE-1743753

In all, 91Ě˝»¨professors make up one-third of the 24 new members, who will be formally inducted in September during an annual meeting at the Museum of Flight in Seattle.

Elected by current members of the Washington State Academy of Sciences:

• , professor of environmental and occupational health sciences
• , associate dean for faculty affairs and professor in the Evans School of Public Policy & Governance
• , professor of chemistry
• , professor of electrical and computer engineering and associate vice provost of research
• , professor and chair of mechanical engineering
• , professor of physics at the 91Ě˝»¨Institute for Nuclear Theory
• , professor of pharmacology and of psychiatry and behavioral sciences

Additionally, , professor of atmospheric sciences and of applied mathematics, was elected to the state academy by virtue of his election into the National Academy of Sciences.

The newly elected members bring the total number of active members to 2,347 and the total number of nonvoting foreign associates to 487.

Bretherton, a 91Ě˝»¨professor jointly appointed in the departments of Atmospheric Sciences and Applied Mathematics, works on clouds and climate. He earned his undergraduate degree from the California Institute of Technology and his doctorate in 1984 from the Massachusetts Institute of Technology. He then did postdoctoral research at the National Center for Atmospheric Research before joining the 91Ě˝»¨faculty in 1985.

Bretherton studies how clouds form and change over time and how to better represent these processes in global climate and weather-forecasting models. His research also looks at the role that clouds may play in climate change.

Bretherton is a fellow of the American Geophysical Union and the American Meteorological Society and a recipient of the Jule G. Charney Award, a career research award from the American Meteorological Society. He was a lead author of the chapter on clouds and aerosols for the from the Intergovernmental Panel on Climate Change, and he is a former director of the UW’s Program on Climate Change.

The National Academy of Sciences is a private, nonprofit institution that was established under a congressional charter signed by President Abraham Lincoln in 1863. It recognizes achievement in science by election to membership, and — along with the National Academy of Engineering and the National Academy of Medicine — provides science, engineering and health policy advice to the federal government and other organizations.

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What they discover will be used to improve climate models, which routinely underestimate how much solar energy bounces off clouds in that region. Simulating how much solar energy is absorbed or reflected on Earth is key to calculating the future of the planet under climate change.

The Southern Ocean Clouds, Radiation, Aerosol Transport Experimental Study, or , could also help scientists understand the very nature of how clouds interact with aerosols — natural or human-made particles that are suspended in the atmosphere. Aerosols can cause clouds to form, change their structure and affect precipitation, all of which affect the amount of energy that reaches the surface.

During the mission, which runs from mid-January through Feb. 25, the scientists are collecting data from air and sea. Observations are being taken from the High-performance Instrumented Airborne Platform for Environmental Research, or HIAPER, a operated by the NSF and the National Center for Atmospheric Research, and the , an Australian deep-ocean research vessel.

“Much of what we currently know about Southern Ocean cloud, aerosol and precipitation properties comes from satellite-based estimates, which are uncertain, and have undergone few comparisons against independent data,” said team member , a 91Ě˝»¨research associate professor of atmospheric sciences. “The data collected during SOCRATES will also enable us to evaluate current satellite data over the Southern Ocean, as well as potentially help in the design of better satellite-based techniques.”

The research aircraft based out of Hobart, Tasmania, will make about 16 flights over the Southern Ocean. Instruments will measure the size and distribution of cloud droplets, ice crystals and aerosols. The data will help test the theory that climate models may not be producing enough water — droplets that stay liquid even when the temperature is below freezing.

Measurements will also provide a look back in time to see how the atmosphere behaved in a time when it contained fewer human pollutants.

“It can be difficult to find truly pristine conditions in the Northern Hemisphere,” said , a 91Ě˝»¨professor of atmospheric sciences. “By studying the more pristine Southern Ocean region, we hope to be able to learn about what conditions may have been like in the Northern Hemisphere in the pre-industrial period.”

The measurements taken from the sky will be complemented by data collected from the R/V Investigator. ĚýThe ship’s team will launch soundings every six hours, and sometimes more often, throughout the campaign.

The U.S. portion of SOCRATES is largely funded by the National Science Foundation.

“The Southern Ocean is famously remote and stormy and it’s hard to imagine a worse place to do a field campaign. But a vast, stormy ocean is a great laboratory for studying clouds, and it’s clear from our models that we have a lot to learn about them,” said Eric DeWeaver, program director in NSF’s geoscience directorate.

SOCRATES investigators will also incorporate other ocean measurements and data from that 91Ě˝»¨scientists installed in 2016.

“SOCRATES will allow for some of the best observations of clouds, aerosols, radiation, and precipitation that have ever been collected over the Southern Ocean,” said principal investigator , at the University of Oklahoma. “These data will provide us with critical insight into the physics of cloud formation in the region, information we can use to improve global climate models.”

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Based on a National Center for Atmospheric Research . For more information, contact Marchand at rojmarch@uw.edu.

The full text of the fifth IPCC report was released today, and 91Ě˝»¨ atmospheric science professors and were among 209 researchers from 39 countries who were lead authors on the 900-page .

“Warming is unequivocal,” Hartmann said Friday at a news conference in Sweden. He was a coordinating lead author for Chapter 2, Observations of Atmosphere and Surface, which reviews the evidence for global warming in temperature records. Hartmann also helped draft the technical summary and the summary for policymakers, and was in Stockholm last week for the final line-by-line reviews of the 36-page .

“For the most part the conclusions of previous IPCC assessments can be given with even more certainty,” Hartmann commented by e-mail. “The surface of Earth is warming and humans are responsible.”

The new report moves from asking whether warming has occurred, he said, to determining exactly how much warming has taken place since 1750, around the beginning of the industrial age. This assessment also makes more forward-looking statements for policymakers.

“Simpler messages with more clarity can be given about how greenhouse gas release is related to future climate change,” Hartmann wrote.

The report recommends that, to keep temperature change within 3.6 degrees F (2 degrees C) of preindustrial levels, carbon emissions should not exceed 1 trillion metric tons. Without changes that level would be reached by 2040, Hartmann said.

While much of the report fills in the details of previous versions, that’s not a bad thing, Bretherton said.

“I think it is important that the basic conclusions of the assessment, about how much warming (will occur) and patterns of rainfall change in a warmer climate, are essentially identical to the previous IPCC assessments,” Bretherton said. He is a lead author on Chapter 7: Clouds and Aerosols, which for the first time was the subject of a separate chapter instead of being discussed in other sections.

“Clouds and aerosols are the single largest source of uncertainty in simulating the climate change of the next 50 to 100 years,” Bretherton said. Models have a hard time simulating clouds, he said, and it’s not well understood how clouds interact with human-produced aerosols such as pollution haze.

Chapter 7 authors also were asked to take a first IPCC look at geoengineering, a controversial idea to start trying to bury carbon dioxide or reflect sunlight by spraying aerosol particles into the top of the atmosphere. The summary text warns of technological limitations and possible side effects from implementing either of these techniques on a global scale.

This IPCC report was an even bigger undertaking than usual, with almost twice as many scientists contributing as last time.

“Maybe the next IPCC assessment, in 2020 or so, will be a much shorter update requiring a lot less effort from the global climate science community,” Bretherton said. “But I won’t bet on it.”

91Ě˝»¨faculty members who were not involved in drafting the report first saw the document Friday, when the summary was released to the public. Most agreed that this assessment reaffirms the science while providing some updates on sea-level rise and ocean changes.

“The biggest difference (between this report and the last one) is our confidence in the results,” said , an oceanography professor and director of the UW’s interdisciplinary . “It contains new information about how ice sheets at the poles are contributing to sea-level rise, changes in the chemistry of the ocean through ocean acidification. Also new are discussions of the long-term changes – of a thousand years or more – that we are already committed to” from long-lived carbon emitted since the beginning of the industrial age.

The full text of Working Group I, on the physical basis for climate change, was released Sept. 30. The reports of the other two IPCC working groups, on the effects of climate change and possible mitigation responses, will follow in 2014.

“The IPCC results emphasize the need to get serious about avoiding dangerous interference with the climate system and on preparing – globally, nationally and locally – for the changes already set in motion,” commented , director of the UW’s and co-author of an upcoming report on climate change impacts on the Pacific Northwest.

A full list of UW-affiliated authors on the report is available .

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For more information, contact Bretherton at 206-685-7414 or breth@atmos.washington.edu, Hartmann atĚý206-543-7460 or dhartm@uw.edu and Snover at 206-221-0222 or aksnover@uw.edu. Hartmann will be in Europe until Oct. 7.