With October in sight, and NOAA predicting a positive phase for the Arctic Oscillation, winter returns to the North Pole. That means, after some prolonged melting in the second half of September, the yearly minimum in the Arctic sea ice extent has been reached.

September 19 turned out to be the day that brought the absolute low for this summer season. On that day 4.6 million square kilometres of ice remained; albeit mostly thin ice, no more than one, perhaps two winters old. It is a decline of some 32 percent compared to ‘normal’: the average for the period of 1979 (start of satellite measurements) to 2000. [For climate comparison it is a dangerous trend to now use the 1979-2009 time period, as witnessed on the NSIDC website. It would mask the big decennial changes.]

This places the 2010 summer extent among the three lowest on record. Only September 2007 en 2009 saw a bigger decline. The trend line seems to continue though.

(c) Rolf Schuttenhelm | www.bitsofscience.org