The new measurements by CU-Boulder's NSIDC show the maximum sea ice extent for 2008-09 reached on Feb. 28 was 5.85 million square miles, which is 278,000 square miles below the average extent for 1979 to 2000, an area slightly larger than the state of Texas, said Meier.
In addition, a team of CU-Boulder researchers led by Research Associate Charles Fowler of the Colorado Center for Astrodynamics Research, or CCAR, has found that younger, thinner ice has replaced older, thicker ice as the dominant type over the past five years, making it more prone to summer melt.
'Ice extent is an important measure of the health of the Arctic, but it only gives us a two dimensional view of the ice cover,' said Meier. 'Thickness is important, especially in the winter, because it is the best overall indicator of the health of the ice cover. As the ice cover in the Arctic grows thinner, it becomes more vulnerable to summer melt.'
Until recent years, measurements have shown most Arctic ice has survived at least one summer and often several, said Meier. But the balance has now flipped, and seasonal ice -- which melts and re-freezes every year -- now comprises about 70 percent of Arctic sea ice in winter, up from 40 to 50 percent in the 1980s and 1990s, he said. Thicker ice that has survived two or more years now comprises just 10 percent of ice cover, down from 30 to 40 percent in years past.
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