By Sid Perkins
From San Francisco, at a meeting of the American Geophysical Union
Satellite observations of the Arctic Ocean show that the amount of sea ice there this year was the lowest it’s been in more than 20 years.
In September, the extent of the sea ice–defined as the area in which ice covers at least 15 percent of the ocean’s surface–was 5.27 million square kilometers, says Julienne C. Stroeve, a climatologist at the National Snow and Ice Data Center in Boulder, Colo. Of that area, sea ice actually covered about 3.6 million square kilometers, a figure 17 percent lower than normal for that time of year and 9 percent below the previous minimum for a September. The earlier record low was set in 1998, during the late stages of the strongest El Nio ever seen and when the global average temperature had been much higher than normal for several months.
Satellites have been monitoring arctic sea ice since 1978. Since then, annual ice coverage has dropped about 3 percent per decade, and September ice coverage has declined 8 percent per decade.
Several factors contributed to the low ice cover this year, says Stroeve. From March through May, southerly winds pushed ice away from the northern shores of Eurasia and North America. Because the open water absorbed more radiation than snow-covered ice would have, the near-shore waters warmed and accelerated melting at the edges of the ice packs. From June through August, unusually warm and persistently stormy conditions blanketed the Arctic Ocean, fracturing the and further fostering melting.
Unlike earlier years with low ice coverage, this year the sea northeast of Greenland was relatively free of ice.
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