Thursday, October 25, 2012

Polar sea ice sets two records

On August 26th this year, Arctic sea ice extent fell to its lowest ever since records began in 1979. Sea ice continued to melt into September reaching a minimum of 3.41 million square kilometers on the 16th of September. Which is 790 thousand square kilometers less than the previous record minimum (2007) and roughly half the average minimum from 1979 to 2000 (7.04 million square kilometers).

At the other end of the planet Antarctic sea ice was setting a new winter maximum of 19.44 million square kilometers on the 26th of September. Which is 740 thousand square kilometers more than the 1979 to 2000 average maximum (18.7 million square kilometers). So the gain in the south is far lower than the loss in the north. And the gain in the Antarctic is no cause for celebration.

Antarctic sea ice extent on the 26th of September when the record maximum was set (image NSIDC)
The gain in sea ice in the Antarctic is likely to be due to two effects. The hole in the ozone layer has a cooling effect on the continent because ozone is a greenhouse gas. Warming in the Southern Ocean, which is well documented, has also lead to an increase in the strength of westerly winds. This has pushed more sea ice away from shore expanding its extent in most places except the Antarctic peninsula where it has decreased.

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