Study Links Arctic Sea Ice Loss With Changes in Atmospheric Circulation

By Emily Shenk

National Geographic

A skier crosses the Arctic Ocean, where the extent of summer sea ice has declined by about 30 percent during the last three decades. Photo by Dan Westergren

study published in the International Journal of Climatology in May adds to the growing research linking melting sea ice in the Arctic to possible changes in atmospheric circulation and extreme weather.

Elizabeth Cassano, lead author of the study, and her team conducted climate model simulations to see how an increase in open water may be affecting the Earth’s atmosphere.

Cassano and her colleagues ran two 30-year simulations, one using climatological sea ice (the average sea ice extent over a period of 51 years), and the other using sea ice extent in 2007, the second lowest year on record.

“We are seeing reduced sea ice extent all year, but it’s quite dramatic at the end of the melt season in September,” Cassano said. Using a computer model known as CAM3, which monitors atmospheric changes using ocean and land data, they compared how the atmosphere responded to additional areas of open water, as seen in 2007.

Previous studies have looked at the effects of reduced sea ice and atmospheric circulation for shorter time periods, however Cassano wanted to see what happened throughout an entire year. She found the most significant atmospheric changes were during autumn and winter, the seasons following the greatest sea ice loss.

There was “an increase in near surface temperature and heat being transported from the areas of open water to the atmosphere,” Cassano said. “This was most dramatic when the season started turning colder.”

Cassano, an associate scientist at the University of Colorado’s Cooperative Institute for Research in Environmental Sciences, said how these impacts will be felt beyond the Arctic is an area of ongoing research. “There’s a possibility of a weaker jet stream,” Cassano said. “What that means is weather systems would move more slowly and there’s a potential for more extreme weather.”

A more meandering jet stream—meaning one that dips north to south rather than taking a straight west to east path—could contribute to temperature extremes in certain areas, Cassano said.

Jennifer Francis, a research professor at Rutgers University’s Institute of Marine and Coastal Sciences, also has studied the impacts of reduced sea ice in the Arctic. “A novel aspect of this study is the comparison of modeled atmospheric response to the actual observed sea-level pressure patterns during 2007,” she said. “Differences between these two help distinguish the changes that are due to sea ice loss from those due to other factors.”

This kind of research is becoming increasingly important as Arctic sea ice melts at alarming rates. According to a 2011 National Geographic magazine article, the extent of summer ice has declined about 30 percent over a period of three decades. Since Cassano’s study was done, 2012 had even lower levels of sea ice than 2007.

Francis, who was not involved in the study, said that these kinds of simulations only tell part of the story when it comes to weather predictions. “These modeling experiments do not include the effects of snow loss or increased water vapor, and thus are missing important influences—perhaps the most important influences—of the warming Arctic on weather patterns,” she said.

Cassano and her colleagues plan to look more closely at the relationship between reduced sea ice extent and weather in the midlatitudes, the temperate zones that include the lower 48 states.

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Christy Ullrich Barcus, National Geographic magazine staff, covers natural history and culture topics for National Geographic News. She is the editor of Polar Bear Watch. She holds a master's degree in nonfiction writing from Johns Hopkins University and a bachelor's degree from the University of Virginia.