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As most of you know, Arctic sea ice reached a record low minimum extent on September 16th. Also last month, Antarctic sea ice achieved a record high maximum extent.
Sea ice in the Arctic is now starting its annual increase as the sun dips toward the horizon.
A total of 11.83 million sq/km of sea ice was lost in the Arctic this past melt season. The previous record loss was 10.65 million sq/km, according to the National Snow and Ice Data Center (NSIDC). The satellite record goes back to 1979.
Air temperatures at the 925 mb level just above the Arctic Ocean averaged 2 to 5 C. (4 to 9 F.) above average for September 2012. One of the reasons for this was the increase in open water, which allows more of the sun's heat to be absorbed.
September 2012 sea ice extent was 16% lower than the previous record low and 45% below the 30-year average (1981-2010).
--The linear rate of decline for September since 1979 is now 13% per decade.
--The Arctic sea ice volume for September likely reached a record low according to PIOMAS...
Excerpts from the NSIDC report......
Entering the melt season, a thinner ice cover made the Arctic sea ice cover more vulnerable to weather, such as the storm that tracked through the Arctic in early August. Because the ice was thin and already decaying by the time of the storm, it was quickly broken up and melted by winds and waves.
Other than the August storm, the pressure pattern in 2012 does not appear to have been as favorable in promoting ice loss as was the case in 2007, and yet a new record low occurred.
-- Only category 4-year old sea ice increased across the Arctic, when you compare the lowest extent years of 2007 with 2012. This 4-year ice will become 5-year ice as the ice growth season begins once again. However, only about 20% of the thicker, 5-year ice is left compared to what there was back in the 1980s. See the NSIDC image below.
As we have stated earlier, there was a record high for sea ice extent in the Antarctic last month.
Important points directly from the NSIDC report about the Antarctic sea ice extent...... Dr. Sharon Stammerjohn of INSTAAR, University of Colorado, provides a review of the differences between Arctic and Antarctic climate controls on sea ice and helps place the events in context.
First, climate is warming over much of the Antarctic continent, as shown in several recent studies (e.g., Steig et al., 2009) and is related to Pacific Ocean warming (Ding et al., 2010) and circumpolar winds. Both warming and ozone loss act to strengthen the circumpolar winds in the south. This is due primarily to persistently cold conditions prevailing on Antarctica year-round, and a cold stratosphere above Antarctica due to the ozone hole. Stronger winds generally act to blow the sea ice outward, slightly increasing the extent, except in the Antarctic Peninsula region, where due to geography, winds from the north have also increased, pushing the ice southward. Thus, sea ice extent near the northwestern Antarctic Peninsula continues to decline rapidly, while areas in the Ross Sea and the southern Indian Ocean show significant increases (Stammerjohn et al., 2012).
Comparing winter and summer sea ice trends for the two poles is problematic since different processes are in effect. An expansion of winter Antarctic ice could be due to cooling, winds, or snowfall, whereas Arctic summer sea ice decline is more closely linked to decadal climate warming.
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