A look at weather extremes and the big-picture climate connections.

Arctic Sea Ice Ties Another Record Low

Monthly February ice extent for 1979 to 2011 shows a decline of 3.0 percent per decade. Credit: NSIDC.

The decline of the Arctic's sea ice cover is one of the most visible manifestations of global climate change. During the past few decades, the rapidly warming Arctic region has seen a steepening decline in its ice cover, particularly during the summer months, to the point where the famed Northwest Passage and Northern Sea Route were both open for navigation at the end of the 2010 summer melt season —possibly heralding a new age of human activities, including shipping and oil drilling, in the Far North.

Although it is doing so at a lesser rate, wintertime sea ice extent is also declining, and this year has been no exception. Thanks in part to weather patterns that have kept much of the Arctic region unusually warm, last month, sea ice extent reached the lowest level on record for the month of February, a record shared with February 2005. According to the National Snow and Ice Data Center (NSIDC) in Boulder, Colo., February ice extent was low in both the Atlantic and Pacific portions of the Arctic — with the most pronounced departures from average in the Labrador Sea and Gulf of Saint Lawrence.

Here's more on February sea ice decline, from NSIDC scientists:

"While ice extent has declined less in winter months than in summer, the downward winter trend is clear. The 1979 to 2000 average is 15.64 million square kilometers (6.04 million square miles). From 1979 through 2003, the February extent averaged 15.60 million square kilometers (6.02 million square miles). Every year since 2004 has had a mean February extent below 15 million square kilometers (5.79 million square miles)."

Air temperatures over most of the Arctic Ocean were above average for the month, including some parts of the East Greenland Sea where temperatures averaged as high as 13°F above average. The lack of sea ice in the Gulf of St. Lawrence poses a threat to harp seals, because they give birth to their pups on the sea ice, typically in February and March. Meanwhile, cooler than average conditions predominated over parts of Eurasia and the Canadian Arctic. 

Arctic sea ice extent for February 2011 was 5.54 million square miles. The magenta line shows the 1979 to 2000 median extent for that month. The black cross indicates the geographic North Pole. Credit: NSIDC.

According to the NSIDC, the lack of sea ice in the Labrador Sea and Gulf of St. Lawrence is partly related to a natural climate pattern known as the Arctic Oscillation, or AO. When the AO is in a negative phase, colder than average conditions are more likely to occur in Europe and the U.S.

The decline of sea ice cover may have significant consequences for Arctic ecosystems, with a new study finding that Arctic plankton blooms are occurring up to 50 days earlier now than they were in the late 1990s. Phytoplankton lie at the base of the marine food chain, and such a major shift in when their populations soar could have ripple effects for other species. 

Study author Mati Kahru, an oceanographer at the Scripps Institution of Oceanography in San Diego, told the Washington Post that the earlier blooms are clearly related to sea ice retreat. "The trend is obvious and significant, and in my mind there is no doubt it is related to the retreat of the ice," Kahru said.

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