Arctic sea ice heads for record low

Going, going? Next month could see Arctic sea ice shrink to its smallest extent yet, beating the previous record, set in 2007. Any such record will be driven by unusual weather, but is also a result of underlying warming.

Arctic sea ice retreats in summer, reaching a minimum in September, but in recent years this summer melt has become more extreme. If the decline continues, Arctic summers could be ice-free by the 2030s.

Data from the National Snow & Ice Data Center in Boulder, Colorado, show that the extent of Arctic ice is smaller than it was at this time in 2007 ? a finding corroborated by the Danish Meteorological Institute's Centre for Ocean and Ice in Copenhagen.

Cloud factor

"It wouldn't surprise me if we had a [record] minimum this year," says Seymour Laxon of University College London. He has unpublished results from satellite data on the volume of Arctic ice. They suggest that, beneath the annual oscillation between summer and winter ice volume, the Arctic has lost up to 900 cubic kilometres of ice each year since 2004.

The 2007 low was made worse by below average cloud cover; more of the sun's heat reached the ice. Further study will probably conclude that unusual conditions added to this year's low too, but climate change is also at work. A new analysis suggests that at least 70 per cent of the ice lost between 1979 and 2010 was caused by our greenhouse gas emissions (Environmental Research Letters, DOI: 10.1088/1748-9326/7/3/034011).

Despite improvements in climate models, the sea ice is still melting faster than the models predict (Geophysical Research Letters, DOI: 10.1029/2012GL052676).

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