Monday, September 5, 2011

Arctic closing in on 2007 melting record

Rolf Schuttenheim in Bits of Science: It´s September and we have about two weeks to go till the annual Arctic sea ice minimum. As far as we can tell it´s going to be a close call – with a good chance that this year will beat all previous melting records. That would then have to include the melting record of 16 September 2007, when the Arctic sea ice extent plummeted to 4.28 million square kilometers – 39% below average.

In the Far North there have already been silent melting records this year. In line with record-low sea ice during the autumn of 2010 in March 2011 the annual sea ice maximum turned out to be the lowest ever – and also in May, June and July there was less ice in the Arctic Ocean than ever before, including record year 2007.

At the end of July and in early August the melting slowed down somewhat – and the ice extent for August 2011 was larger than for August 2007. However in recent days the ice graph has kept a steady declining course and with just two weeks to go till the expected minimum, 2007 and 2011 are now in a neck and neck race, as the daily updates of the NSIDC show.

Much now will depend on the Arctic weather for the rest of the month, which means we can actually consult weather forecasts to get an idea of what might turn out. Normally we can simply look to the North Atlantic Oscillation index, which describes the air pressure differences between the Arctic and lower latitudes. ‘A negative NAO’ implies high pressure over the Arctic and relatively warm air sinking down from adjacent regions, promoting further ice loss.

NOAA in its ensemble forecast expects the NAO index has for the next two weeks about even chances of turning to a negative phase as it has to turn to a positive phase [although perhaps the latter would be slightly favoured]....

Graphic comparing Arctic sea ice extent year by year from the National Snow and Ice Data Center

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