"Satellite radar and lidar measurements allow us to observe Arctic clouds in a new way," says CSU scientist Tristan L'Ecuyer, a co-author of the study. "These new instruments not only provide a very precise view of where clouds exist but also tell us their height and thickness, which are key properties that determine the amount of sunlight clouds reflect back to space."
The research team also examined longer-term records of Arctic cloud and weather patterns, including a 62-year-long record of cloudiness from surface observations at Barrow, Alaska. They found that the 2007 weather and cloud pattern was unusual but not unprecedented. At Barrow, five other years--1968, 1971, 1976, 1977, and 1991--had less summertime cloud cover than 2007, but without the same impact on sea ice.
-----A summer feedback cycle-----
The research suggests that warmth from the Sun will increasingly affect Arctic sea ice loss in the summer. As the ice shrinks, incoming sunshine triggers a spiraling effect: the newly exposed dark ocean waters, much darker than the ice, absorb the Sun's radiation instead of reflecting it. This warms the water and melts more ice, which in turn leads to more absorption of radiation and still more warming.
"Our research indicates that the relative importance of solar radiation in the summer is changing," Kay says. "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."
The authors note that, in addition to solar radiation, other factors such
|Contact: David Hosansky, NCAR Media Relations|
National Center for Atmospheric Research/University Corporation for Atmospheric Research