Washington, April 22 : A new study by scientists at the National Center for Atmospheric Research (NCAR) and Colorado State University (CSU), US, has shown that the shrinking expanse of Arctic sea ice is increasingly vulnerable to summer sunshine.
The study finds that 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.
Drawn on observations from instruments on a new group of NASA satellites known as the "A-Train," the study was funded by NASA and the National Science Foundation.
According to NCAR's Jennifer Kay, the lead author of the study, "In a warmer world, the thinner sea ice is becoming increasingly sensitive to year-to-year variations in weather and cloud patterns."
"A single unusually clear summer can now have a dramatic impact," she added.
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.
Last summer's loss of Arctic sea ice set a modern-day record, with the ice extent shrinking to a minimum of about 4.1 million square kilometers in September, which 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 sunshine was strong enough to melt about a foot of surface ice. Over open water, it was sufficient to increase sea-surface temperatures by 2.4 degrees Celsius.
Warmer ocean waters can contribute to sea ice loss by melting the ice from the bottom, thereby thinning it and making it more susceptible to future melt.
The research suggested that warmth from the Sun will increasingly affect Arctic sea ice loss in the summer.
"Our research indicates that the relative importance of solar radiation in the summer is changing," said Kay. "The sunshine reaching the Arctic is increasingly influential, as there is less ice to reflect it back into space. Dry, sunny conditions in a single summer can now act as a potent force to melt sea ice," she added.