Only in 2007, with unusual climatic conditions hastening its reduction, did sea ice dwindle more severely than in 2011. According to NASA, average ice extent for September 2011 was 1.78 million square miles, nearly a million square miles below the 1979-2000 average.

For the past five years, ice extent for the month of September has been the lowest in satellite records. This year, climatic conditions were similar, but not as extreme, as those in 2007, when ice extent reached its minimum. This year, temperatures in the Beaufort and Chukchi Seas were near average, although north of Greenland and in Canadian Archipelago, conditions were even warmer than in 2007. Data indicate above normal temperatures on the surface of the Arctic Ocean in 2011, although temperature anomalies were not as extreme as in 2007.

Ice remains younger, thinner

Data on ice age show that coverage of the oldest, thickest ice types (ice four years or older) has declined over the past 28 years. First- and second-year ice made up 80% of the ice cover in the Arctic Basin in March 2011, compared to 55% on average from 1980 to 2000.

As in recent years, northern shipping routes opened up this summer. Both the Northwest Passage and the Northern Sea Route were open for a period during September.