Klimaatverandering 113

Science, October 2007

'IS BATTERED ARCTIC SEA ICE DOWN FOR THE COUNT?

[Rachel's introduction: "This [arctic] ice is more vulnerable than we thought." And that vulnerability seems to be growing from year to year, inspiring concern that Arctic ice could be in an abrupt, irreversible decline.]
By Richard A. Kerr

A few years ago, researchers modeling the fate of Arctic sea ice under global warming saw a good chance that the ice could disappear, in summertime at least, by the end of the 21st century. Then talk swung to summer ice not making it past mid-century. Now, after watching Arctic sea ice shrink back last month to a startling record-low area, scientists are worried that 2050 may be overoptimistic."This year has been such a quantum leap downward, it has surprised many scientists," says polar researcher John Walsh of the University of Alaska, Fairbanks. "This ice is more vulnerable than we thought." And that vulnerability seems to be growing from year to year, inspiring concern that Arctic ice could be in an abrupt, irreversible decline. "Maybe we are reaching the tipping point," says Walsh.There's no doubt that 2007 was a special summer melt season. The ice area remaining in September--the year's low point--had been shrinking since satellite monitoring began in 1979. Some years it recovered a bit, others it declined further, but overall it shrank 8.6% per decade. In 2005, it hit a record low of 5.6 million square kilometers, down 20% from 1979. But last month, "we completely blew 2005 out of the water," says sea ice specialist Mark Serreze of the University of Colorado, Boulder. Ice area plummeted to 4.13 million square kilometers, down 43% from 1979. That's a loss equivalent to more than two Alaskas. The new low is more than one Alaska below the trend line. Nothing else like that appears in the satellite record or, for that matter, in monitoring from ships and planes during the rest of the 20th century, says Walsh. An immediate cause of the record-breaking year is clear enough. As Serreze explains, an unusually strong high- pressure center sat over the central Arctic Ocean while a strong low hovered over Siberia. This weather pattern allowed more solar heat through the clear skies beneath the high-pressure center and pumped warm air up from the south between the high and the low.'

lees verder: http://www.precaution.org/lib/07/prn_can_arctic_sea-ice_recover.071005.htm