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Warm summer means cold winter

Warmer climate, spurred by climate change, can cause colder winters. This is the result of a new study by Jodah Cohen, released this week.

The study explains the Rube Goldberg-machine of climatic processes that can link warmer-than-average summers to harsh winter weather in some parts of the Northern Hemisphere.

Average temperatures have risen for over 200 years, most rapidly for the past 40 years. And average temperatures in the Arctic have been rising at nearly twice the global rate, says Cohen, a climate modeler at the consulting firm Atmospheric and Environmental Research in Lexington, Massachusetts.

A close look at climate data from 1988 through 2010, including the extent of land and sea respectively covered by snow and ice, helps explain how global warming drives regional cooling, Cohen and his colleagues report.

The strong warming in the Arctic in recent decades, among other factors, has triggered widespread melting of sea ice. More open water in the Arctic Ocean has led to more evaporation, which moisturizes the overlying atmosphere, the researchers say. Previous studies have linked warmer-than-average summer months to increased cloudiness over the ocean during the following autumn.

That, in turn, triggers increased snow coverage in Siberia as winter approaches. As it turns out, the researchers found, snow cover in October has the largest effect on climate in subsequent months.