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By Michael McCarthy Environment Editor
24 September 2003

The largest ice shelf in the Arctic, a solid feature for at least 3,000 years, has broken in two and climate change is to blame, say American and Canadian scientists.

The Ward Hunt ice shelf, on the north coast of Ellesmere Island in Canada, has split down the middle, and a freshwater lake held behind it has drained away, the researchers say.

Reporting in the journal Geophysical Research Letters, the scientists say the fracture, which had been developing since 2000, was further evidence of continuing and accelerating climate change in the north polar region.

Much evidence suggests that the sea ice covering the Arctic Ocean is rapidly thinning and retreating, with reports two years ago that at one stage the North Pole itself was actually seawater rather than ice.

The break-up of the ice shelf - floating ice attached to land - shows a relatively rapid temperature rise. The ice, which formed a cap at the end of the 20-mile long Disraeli fjord, was the largest remaining piece of an ice shelf that once ran the length of Ellesmere Island.

It began to break up 100 years ago and by 1982 about 90 per cent of it was gone, but it then stabilised over the next two decades, say the scientists, Warwick Vincent and Derek Mueller of Laval University in Quebec City, and Martin Jefferies of the University of Alaska at Fairbanks.

However, in April 2000, satellite images showed the beginnings of cracking from the eastern side of Ward Hunt Island into the fjord, and by 2001 it had split along its length, then widened in 2002 to 85 yards in some places.

It has spawned several ice islands, some large enough to endanger shipping and drilling platforms in the Beaufort Sea.

A layer of freshwater on the top of the fjord that was dammed by the shelf, and contained a unique ecosystem rare plankton and other life, has drained into the Arctic Ocean.

The Ward Hunt shelf was up to 100ft thick, far thicker than the sea ice on the Arctic Ocean's surface, which averages 10ft.

The researchers said its disintegration seemed to have been prompted by a century-old local warming trend, and a more recent rapid rise in temperatures. They were not certain it was linked to the man-made warming apparently caused by rising concentrations of greenhouse gases, but it was one of many signs the Arctic is seeing enormous climatic changes.

"We believe it's part of a long-term process," said Dr Vincent, a biologist in polar ecology. "But the most recent changes are substantial and correlate with this recent increase in warming seen from the 1960s to the present. A critical threshold has been passed."

"It is accepted that should the global climate start to warm, the effects would be felt first in the polar regions, and they would be amplified," said Dr Jefferies, a geophysicist.

"This could be part of that signal." Recent records show there has been a local increase of 0.4 degrees C every decade since 1967. Since then the average July temperature has been above freezing, at 1.3C.

Professor Julian Dowdeswell, director of Britain's Scott Polar Research Institute in Cambridge, said the break-up of Ward Hunt ice shelf was not caused by man-made climate change, but by the natural end of a period known as "the little ice age". But he said recent changes in sea-ice thickness and extent could be manifestations of global warming, and the break-up of Ward Hunt could be part of that pattern.

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