Sunday, March 4, 2012

Less sea ice brings more snow

Devin Powell in Science News: Global warming may be responsible for the Northern Hemisphere's recent bout of severe winters. As Arctic sea ice melts, it funnels cold air toward the equator and sets the stage for snow, a new study finds.

“When we have a dramatic reduction in sea ice, we end up with more snow,” says climate scientist Jiping Liu of the Georgia Institute of Technology in Atlanta and coauthor of the study, published online February 27 in the Proceedings of the National Academy of Sciences.

Despite rising global temperatures, extreme winters have blasted much of the Northern Hemisphere during the last decade. Unusually large snowstorms pummeled the United States’ east coast during the winters of 2009 to 2010 and 2010 to 2011. Parts of Japan saw record levels of snow this winter, while in Europe both the Danube and Venice's canals froze over, a rare sight.

To explain this bitter cold and snow, some scientists have turned to natural climate fluctuations — including El Niño, a periodic warming of the eastern Pacific Ocean thought to portend warmer and drier winter conditions. But since some severe winters coincided with El Niño years, Liu's team looked instead to sea ice floating in the Arctic, a region that has been warming twice as quickly as the average rate for the Northern Hemisphere.

...Computer simulations published in 2009 in Geophysical Research Letters found that such a pressure system can push cold air out of the Arctic and into Eurasia. A case study of Europe’s 2005-2006 winter, reported in 2010 in the Journal of Geophysical Research, suggested that cold air blowing in from the Arctic increases by threefold the chance of cold winter extremes in Europe.

Disappearing sea ice may also provide more moisture for forming snow, says Liu. In further simulations by his team, open water no longer covered by ice released vapor that traveled to parts of Europe and Asia....

Loss of Arctic sea ice cover between 1979 and 2010 coincided with more winter snow in parts of the United States, China and Europe (redder areas indicate more snowfall attributable to sea ice loss). Credit: Google Maps/Jiping Liu

No comments: