Jul 25, 2012
By Deborah Zabarenko
(Reuters)
For a few days this month, NASA's images of the Greenland ice sheet turned red, indicating that for a while, almost the entire surface of the vast frozen island was melting.
The big melt in Greenland is part of an overall picture of an unusually warm season across the Arctic, with much of the sea route from Western Europe to the Pacific as free of ice in July as it normally would be by summer's end, the chief of the U.S. National Snow and Ice Data Center said on Wednesday.
On an average summer, about half of Greenland's surface ice melts, according to NASA. This summer, satellites showed about 97 percent of the ice sheet thawed at some point in mid-July.
The change was swift, as seen in images...
On July 8, there was a big white area in the middle of the image, indicating that 40 percent of Greenland's surface had thawed; by July 12, virtually the whole island was pictured as red, showing widespread defrosting.
For Mark Serreze, director and senior research scientist at the Colorado-based National Snow and Ice Data Center, one interesting aspect of the Greenland event is its relative rarity.
This kind of comprehensive surface melting might happen about every 150 years or so in Greenland, which would make this year unusual but not unprecedented, Serreze said by telephone.
However, he said, most of the previous events were clustered around a period 7,000 years ago known as the Holocene Thermal Maximum, when variations in the sun's tilt on its axis sent more sunshine to extreme northern latitudes, warming them up. There is no such solar tilt going on now, but the melt is occurring just the same...
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