PULLMAN, Wash. – Clouds can increase warming in the changing Arctic region more than scientists expected, according to a new study published Dec. 10 in the journal Nature Communications.
Read the study at http://www.nature.com/ncomms/2015/151210/ncomms10117/full/ncomms10117.html.
“As the Arctic atmosphere warms and moistens, it better insulates the surface,” said Christopher Cox, lead author of the paper. “While we expected this to reduce the influence from clouds, we find that clouds forming in the Arctic appear to further warm the surface, especially in the fall and winter.”
“The effect of clouds is very important for the future of the Arctic,” said Von P. Walden, a co-author and Washington State University professor of civil and environmental engineering. “As the Arctic warms due to global climate change, we’re already experiencing a rapid decrease in snow and ice. Clouds are a big contributor to the balance of energy at the surface and, therefore, have a big impact.”
In the Arctic, the impact of clouds on climate is particularly difficult to understand, said Cox, a research scientist with the Cooperative Institute for Research in Environmental Sciences (CIRES) and the National Oceanic and Atmospheric Administration’s Earth System Research Laboratory. Their role in warming the surface is determined primarily by humidity, temperature and the properties of the clouds.
“The roles that temperature and humidity play is different in the Arctic, where the air is colder and drier than at lower latitudes,” he said.
Cox and colleagues from CIRES, WSU and the University of Idaho analyzed measurements from three science research stations in the far north: Barrow, Alaska; Eureka, Canada; and Summit, Greenland. They assessed temperature, relative humidity and cloud insulating properties and looked at how those factors interacted with one another in different parts of the infrared spectrum.
Previous work suggested that as the atmosphere warms and becomes moister, it becomes a better insulator, so the clouds themselves have a diminishing contribution to warming. This is likely true on a global scale.
However, the team found a different behavior as temperature and humidity increase in the cold Arctic. There, clouds retain their ability to warm the surface and actually amplify regional warming.
The effect – strongest in autumn and winter – is related to the way that temperature and moisture are changing relative to each other, according to the new analysis. The team relied on climate modeling as well as observations to show that the effect is already occurring in the Arctic and is expected to increase in the future as the climate warms.
“We’re seeing what climate change in the Arctic looks like,” said Walden. “As we go forward in time, it is essential to better understand how the humidity changes in a warmer atmosphere. This is key to understanding how clouds warm the surface,” he said.
The study is an example of interdisciplinary work emphasized by WSU’s Grand Challenges, areas of research addressing some of society’s most complex issues.
Because there is little sunlight in the Arctic in autumn and winter, the insulating properties of clouds far outweigh their shading properties, making this result all the more important, said co-author Matthew Shupe, also a CIRES researcher who works at NOAA.
He and his colleagues said their findings call for better monitoring of changes in the Arctic atmosphere, including temperature and moisture levels as well as cloud properties, and continued work to improve the representation of clouds in computer models designed to understand the rapidly evolving Arctic region.
The research was partially funded by the National Science Foundation’s Integrated Characterization of Energy, Clouds, Atmospheric State and Precipitation at Summit (ICECAPS) project.