Climate: Arctic sea ice lingers below average


November ice extent the third-lowest on record

By Summit Voice

Arctic sea ice cover grew at an average pace through November, but after starting at near-record low levels, the extent remained far below average, according to the monthly report from the National Snow and Ice Data Center.

Overall, the Arctic gained 2.36 million square kilometers (911,000 square miles) of ice during the month, slightly more than the average November ice gain.  At the end of the month, sea ice covered 4.19 million square miles, the third-lowest in the satellite record for the month, behind 2006 and 2010.

The linear rate of decline for November during the satellite era is now 53,200 20,500 square miles per year, about 4.7 about per decade relative to the 1979 to 2000 average.

Low sea ice extent this summer may be contributing to warmer November temperatures and lower November ice extents in some areas. Norway, for example, reported the warmest November on record. The record warmth in parts of Scandinavia is probably linked with the current positive phase of the Arctic Oscillation.

In recent years, low sea ice extent in the summer has been linked to unusually warm autumn air temperatures, resulting from the larger areas of open water that absorb more heat during the summer. This heat must escape back to the atmosphere in the fall, before the ocean can freeze over. This escaping heat contributes to warmer-than-average conditions, which have been most apparent in October but may also extend into November.

Typically by November, much of Scandinavia is already covered with snow, but maps from the Rutgers University Global Snow Lab show that snow cover levels were anomalously low over Scandinavia and northwestern Europe during November. Below-normal snow conditions were also evident over most of the continental United States, except for the northern Rockies.

The overall Northern Hemisphere snow cover was more extensive than normal this November, with most of the extra coverage in Canada and Russia, putting November 2011 into the record books as having the fourth most extensive cover in the past 46 years of satellite-derived snow cover records.

Since reaching its seasonal maximum in September, Antarctic sea ice has been near average in recent months. In November, Antarctic extent was 16.15 million square 6.24 million square miles, 87,000 square kilometers (33,600 square miles) less than the 1979 to 2000 average. In recent years, the sea ice cover that surrounds the Antarctic continent has been higher than average, even reaching near-record highs.

Antarctic sea ice varies much more from year to year than Arctic sea ice, but overall, ice extent around Antarctica has been growing slightly over the past 30 years. The ice cover around Antarctica also varies widely by region, with some regions, for example the Amundsen and Bellingshausen seas, showing strong declines over the past three decades, while other regions such as the Ross Sea have seen significant increases.

For more information on Antarctic sea ice, see All About Sea Ice: Antarctic vs. Arctic. Antarctic sea ice data are available from the Sea Ice Index.


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