Arctic ice more vulnerable to sunny weather, new s...( BOULDER--The shrinking expanse of Ar...)

BOULDER--The shrinking expanse of Arctic sea ice is increasingly vulnerable to summer sunshine, new research concludes. The study, by scientists at the National Center for Atmospheric Research (NCAR) and Colorado State University (CSU), finds that unusually sunny weather contributed to last summer's record loss of Arctic ice, while similar weather conditions in past summers do not appear to have had comparable impacts.

The study, which draws on observations from instruments on a new group of NASA satellites known as the "A-Train," will be published tomorrow in Geophysical Research Letters. It was funded by NASA and the National Science Foundation, which is NCAR's principal sponsor.

"In a warmer world, the thinner sea ice is becoming increasingly sensitive to year-to-year variations in weather and cloud patterns," says NCAR's Jennifer Kay, the lead author. "A single unusually clear summer can now have a dramatic impact."

The findings indicate that summer sunshine in the Arctic produces more pronounced melting than in the past, largely because there is now less ice to reflect solar radiation back into space. As a result, the presence or absence of clouds now has greater implications for sea ice loss.

-----Satellite data offer clues to record-shattering 2007 melt-----

Last summer's loss of Arctic sea ice set a modern-day record, with the ice extent shrinking to a minimum of about 1.6 million square miles (4.1 million square kilometers) in September. That was 43 percent less ice coverage than in 1979, when accurate satellite observations began.

Looking at the first two years of data from radar and lidar on the A-Train satellites, Kay and her colleagues found that total summertime cloud cover in the Western Arctic was 16 percent less in 2007 than the year before. A strong high-pressure system centered north of Alaska kept skies relatively clear. Over a three-month period in the summer, the increased sunshin
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