Arctic sea ice extent settles at record seasonal minimum

19 September 2012 (NSIDC) – On 16 September 2012, sea ice extent dropped to 3.41 million square kilometers (1.32 million square miles). This appears to have been the lowest extent of the year. In response to the setting sun and falling temperatures, ice extent will now climb through autumn and winter. However, a shift in wind patterns or a period of late season melt could still push the ice extent lower. The minimum extent was reached three days later than the 1979 to 2000 average minimum date of September 13. This year’s minimum was 760,000 square kilometers (293,000 square miles) below the previous record minimum extent in the satellite record, which occurred on September 18, 2007. This is an area about the size of the state of Texas. The September 2012 minimum was in turn 3.29 million square kilometers (1.27 million square miles) below the 1979 to 2000 average minimum, representing an area nearly twice the size of the state of Alaska. This year’s minimum is 18% below 2007 and 49% below the 1979 to 2000 average. Overall there was a loss of 11.83 million square kilometers (4.57 million square miles) of ice since the maximum extent occurred on March 20, 2012, which is the largest summer ice extent loss in the satellite record, more than one million square kilometers greater than in any previous year. The six lowest seasonal minimum ice extents in the satellite record have all occurred in the last six years (2007 to 2012). In contrast to 2007, when climatic conditions (winds, clouds, air temperatures) favored summer ice loss, this year’s conditions were not as extreme. Summer temperatures across the Arctic were warmer than average, but cooler than in 2007. The most notable event was a very strong storm centered over the central Arctic Ocean in early August. It is likely that the primary reason for the large loss of ice this summer is that the ice cover has continued to thin and become more dominated by seasonal ice. This thinner ice was more prone to be broken up and melted by weather events, such as the strong low pressure system just mentioned. The storm sped up the loss of the thin ice that appears to have been already on the verge of melting completely. The spatial pattern of ice extent at this year’s seasonal minimum is different than that observed for 2007. This year the ice is more extensive in some parts of the central Arctic Ocean. However, the ice is less extensive this year compared to 2007 in the Beaufort Sea, the western Laptev Sea, the East Greenland Sea, and parts of the Canadian Archipelago. As mentioned in our previous post, the Northern Sea Route opened around mid August this year, compared to 2007 when a tongue of ice extended to the coast, blocking the route throughout the summer.