Tuesday, April 7, 2009

Arctic Sea Ice Thinner + Positive Feedback Loop

This data visualization from the AMSR-E instrument on the Aqua satellite show the maximum sea ice extent for 2008-09, which occurred on Feb. 28, 2009. Credit: NASA Goddard’s Scientific Visualization Studio

Until recently, the majority of Arctic sea ice survived at least one summer and often several. But things have changed dramatically, according to a team of University of Colorado, Boulder, scientists led by Charles Fowler. Thin seasonal ice — ice that melts and re-freezes every year — makes up about 70 percent of the Arctic sea ice in wintertime, up from 40 to 50 percent in the 1980s and 1990s. Thicker ice, which survives two or more years, now comprises just 10 percent of wintertime ice cover, down from 30 to 40 percent.

According to researchers from the National Snow and Ice Data Center in Boulder, Colo., the maximum sea ice extent for 2008-09, reached on Feb. 28, was 15.2 million square kilometers (5.85 million square miles). That is 720,000 square kilometers (278,000 square miles) less than the average extent for 1979 to 2000.

“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 Walter Meier, research scientist at the center and the University of Colorado, Boulder. “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 grows more vulnerable to melting in the summer.”

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