Arctic ice: Less than meets the eye

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The CCGS Amundsen makes light work of unexpectedly thin ice.
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The ice may not retreat as much as feared this year, but what remains may be more rotten than robust

LAST September, David Barber was on board the Canadian icebreaker CCGS Amundsen (pictured), heading into the Beaufort Sea, north of Alaska. He was part of a team investigating ice conditions in autumn, the time when Arctic sea ice shrinks to its smallest extent before starting to grow again as winter sets in.

Barber, an environmental scientist at the University of Manitoba in Winnipeg, Canada, went to sleep one night at midnight, just before the ship was due to reach a region of very thick sea ice. The Amundsen is only capable of breaking solid ice about a metre thick, so according to the ice forecasts for ships, the region should have been impassable.

Yet when Barber woke up early the next morning, the ship was still cruising along almost as fast as usual. Either someone had made a mistake and the ship was headed for catastrophe, or there was something very wrong with the ice, he thought, as he rushed to the bridge in his pyjamas.

On the surface, the situation in the Arctic looks dramatic enough. In September 2007, the total extent of sea with surface ice shrank further than ever recorded before - to nearly 40 per cent below the long-term average. This low has yet to be surpassed. But the extent of sea ice is not all that matters, as Barber found. Look deeper and there are even more dramatic changes. This is something everyone should be concerned about because the transformation of the Arctic will affect us all.

The record low in 2007 cannot be blamed on global warming alone; weather played a big role too. That year saw a build-up of high pressure over the Beaufort Sea and a trough of low pressure over northern Siberia - a weather pattern called the Arctic dipole anomaly. It brings warm, southerly winds that increase melting. The winds also drive sea ice away from the Siberian coast and out of the Arctic Ocean towards the Atlantic, where it melts.

In 2008 and 2009, the dipole anomaly did not dominate and the extent of ice did not shrink as much during summer. This rebound led to much talk of a recovery in Arctic ice.

This June, the dipole anomaly returned and the ice extent for the month was the lowest ever. In July, however, the dipole pattern broke up and the rate of ice loss slowed. "Whether or not we set a new record depends very much on the weather patterns," says Mark Serreze of the US National Snow and Ice Data Center based in Boulder, Colorado, which monitors the extent of sea ice - a particular way of measuring its area.

More: http://www.newscientist.com/article/mg20727751.300-arctic-ice-less-than-meets-the-eye.html