Is declining sea ice changing the atmosphere?

Although Arctic sea ice extent did not set a low record this year, it’s still clear that there is less sea ice than there used to be. Scientists are keeping a close eye not only on the dwindling ice, but also on the ripple effect its loss might have on the rest of the Arctic environment. A big question involves the exchange of heat between ocean and air—and the weather patterns that result.  What does current research say about how floating ice—or the lack of it—might be changing the Arctic atmosphere? The seasons of ice and water
Data image showing the record low Arctic sea ice extent in 2012 This data visualization shows the record low Arctic sea ice extent on August 26, 2012. With less ice to reflect sunlight, larger areas of open water absorb more of the sun’s heat. This heat slowly escapes into the atmosphere, causing atmospheric heating during the Arctic autumn. Image credit: Scientific Visualization Studio, NASA Goddard Space Flight Center

Sea ice acts like a reflective cap on the ocean. When there is a lot of bright, white snow and ice, it reflects sunlight back into the atmosphere, insulating the region and maintaining lower temperatures. But less ice exposes more dark ocean, which absorbs the sun’s energy and raises the ocean temperature. This can disrupt the seasonal heat exchange between the Arctic Ocean and atmosphere, which in turn influences polar weather patterns. Elizabeth Cassano, a researcher at the University of Colorado, was part of a team that examined this connection using two thirty-year computer model simulations. One model used climatological sea ice levels at the end of the 20th century; the other used sea ice levels during 2007, a record-low year for sea ice. The model results showed that during spring and summer there was little correlation between sea ice and atmospheric circulation patterns. But during autumn and winter, lower sea ice levels may be heating things up. Cassano said, “What we found is that in the fall and early winter, you have this open water pushing later into the fall when the air—the atmosphere—is getting colder and colder.” But without a protective coating of sea ice, the open water remains relatively warm. “So you have this large temperature difference between the surface and the atmosphere,” she said. Their findings suggest that in the fall, the heat absorbed by the relatively warm ocean escapes into the cooling air, causing atmospheric heating and shifts in typical Arctic weather patterns. “In the fall and early winter, the models simulated lower pressure over much of the Arctic,” Cassano said. “Lower pressure is associated with stormier weather.” High pressure, on the other hand, often results in calm, clear days. “So this suggests that this additional open water may lead to lower pressure and maybe stronger weather patterns,” she said. Ice and weather
Data image showing loops in the jet stream The jet stream swirls around the Northern Hemisphere, created by the convergence of cold air masses descending from the Arctic and rising warm air from the tropics. Scientists are investigating how declining sea ice might be changing the path and speed of the jet stream and leading to strange weather patterns further south.
Image credit: NASA’s Goddard Space Flight Center

This imbalance may be changing the atmosphere not only in the Arctic, but influencing weather elsewhere on the planet. A previous Icelights post, Arctic sea ice and U.S. weather, examined how decreasing Arctic sea ice extent might be weakening the jet stream, the meandering air current that circles the Northern Hemisphere. In years of low sea ice, the jet stream weakens and slows, sending loops of air currents further south. These loops can produce extreme weather patterns, such as pounding one region with an unusual flurry of blizzards or parching a normally wet area with an extended drought. “Our study only looked at the regional impacts,” Cassano said. “The links between the additional open water in the Arctic and weather in the middle latitudes is still very much an open research question.”  As the Northern Hemisphere heads into another winter, scientists will continue to study whether heating in the Arctic may be changing the North Pole atmosphere, the jet stream, or even the globe’s weather. References Cassano, E. N., J. J. Cassano, M. E. Higgins, and M. C. Serreze. 2013. Atmospheric impacts of an Arctic sea ice minimum as seen in the Community Atmosphere Model. International Journal of Climatology, doi:10.1002/joc.3723. NASA Visualization Explorer: Areal Superhighway Related Icelights post Arctic sea ice and U.S. weather