31. Arctic Melt Accelerates

By Douglas FoxJan 22, 2013 6:00 AM
Satellites show the extent of Arctic sea ice on Sept. 16, 2012 as compared to the average minimum from the past 30 years (yellow line). | NASA/Goddard Scientific Visualization Studio


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Arctic sea ice, in retreat for years, shrank to its lowest extent in recorded history this past summer. At its minimum on September 16, the ice covered an area about the size of India; that is 18 percent smaller than the previous record low, set in 2007. The past year’s Arctic melting may have excited shipping companies with the prospect of new ice-free maritime routes, but it is having climate repercussions far from the North Pole.

“The intervals between the records are shorter and shorter. The changes are accelerating,” says Ronald Kwok, a polar scientist at the NASA Jet Propulsion Laboratory in Pasadena. Satellite data show that the annual minimum for Arctic sea ice area fell 7 percent per decade between 1980 and 2000—but since 2000 it has fallen 14 percent per decade. Rapid thinning of the ice is driving that acceleration, says Julienne Stroeve, a climatologist at the National Snow and Ice Data Center in Boulder, Colorado. Rising polar temperatures caused the average thickness of winter Arctic sea ice to decrease from about 12 feet to 6 feet between 1978 and 2008, and thinner ice melts more readily.

The changes produce a feedback loop. Less sea ice contributes to an even warmer Arctic, since dark ocean water absorbs more solar radiation than white, reflective ice. That warming, in turn, is leading to slower east-west winds in the jet stream and slower-moving weather systems across the Northern Hemisphere. Even moderate storm systems can cause extreme flooding if they travel slowly, as residents of southern Spain experienced last September, when heavy rains triggered flash floods that killed 10. The recurring message from climate science: It’s a small world after all.

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