February 28, 2012
Diminishing Arctic Sea Ice Linked To Colder, Snowier Winters
Melting Arctic sea ice will mean colder winters with more snow in the Northern Hemisphere, according to a new study published Monday in the Proceedings of the National Academy of Sciences.
The research provides further evidence of a relationship between melting ice in the Arctic regions and extensive cold outbreaks across northern continents.
The levels of Arctic sea ice set a new record low in 2007, which was followed by significantly above-normal winter snow cover in large parts of the northern United States, northwestern and central Europe and northern and central China.
For instance, during the winters of 2009-2010 and 2010-2011 the Northern Hemisphere measured its second and third largest snow cover levels on record.
"Our study demonstrates that the decrease in Arctic sea ice area is linked to changes in the winter Northern Hemisphere atmospheric circulation," said Judith Curry, chair of the School of Earth and Atmospheric Sciences at Georgia Tech.
"The circulation changes result in more frequent episodes of atmospheric blocking patterns, which lead to increased cold surges and snow over large parts of the northern continents,” she said.
The scientists expanded on previous research by combining observational data and model simulations to study the link between unusually large snowfall amounts in the Northern Hemisphere in recent years and diminishing Arctic sea ice.
They analyzed observational data gathered between 1979 and 2010 and found that a decrease in autumn Arctic sea ice of 1 million square kilometers — roughly the surface area of Egypt -- corresponded to significantly above-normal winter snow cover in large parts of the northern U.S., northwestern and central Europe, and northern and central China.
The analysis revealed two primary contributing factors to this link -- changes in atmospheric circulation and changes in atmospheric water vapor content, both of which are linked to diminishing Arctic sea ice.
Strong warming in the Arctic through the late summer and autumn also seems to be enhancing the melting of sea ice, the researchers said.
"We think the recent snowy winters could be caused by the retreating Arctic ice altering atmospheric circulation patterns by weakening westerly winds, increasing the amplitude of the jet stream and increasing the amount of moisture in the atmosphere," said Jiping Liu, senior research scientist in the School of Earth and Atmospheric Sciences at Georgia Tech.
"These pattern changes enhance blocking patterns that favor more frequent movement of cold air masses to middle and lower latitudes, leading to increased heavy snowfall in Europe and the Northeast and Midwest regions of the United States."
Diminishing Arctic sea ice can cause changes in atmospheric circulation that lead to a circulation pattern that is different than the "negative phase" of the Arctic Oscillation.
In addition to analyzing observational data, the researchers assessed the impact of the diminishing Arctic sea ice on atmospheric circulation by comparing the results of model simulations run with different sea ice distribution.
They ran one experiment that assumed seasonally varying Arctic sea ice, using sea ice concentration data collected between 1979 and 2010. A second simulation incorporated prescribed sea ice loss in autumn and winter based on satellite-derived Arctic sea ice concentrations.
The simulations showed that diminishing Arctic sea ice induced a significant surface warming in the Arctic Ocean and Greenland/northeastern Canada, and cooling over northern North America, Europe, Siberia and eastern Asia.
The models also showed above-normal winter snowfall in large parts of the northern United States, central Europe, and northern and central China.
The consistent relationships seen in the model simulations and observational data illustrate that the rapid loss of sea ice in summer and delayed recovery of sea ice in autumn modulates snow cover, winter temperature and the frequency of cold air outbreaks in northern mid-latitudes.
Liu said more research is needed before any determination can be made about whether the link between Arctic sea ice and increased snowfall can be attributed to climate change or natural variability.
The study was published February 27 in the online early edition of the journal Proceedings of the National Academy of Sciences.
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