The ocean area covered by Arctic sea ice last summer was as low as it has ever been, according to a study.
And the rate of melting gets faster every year, suggesting that a self-perpetuating warming cycle predicted by climate change models is already at work, the study by the main U.S. centre for ice studies said.
"Sea ice is not doing well, and it has not recovered, and it doesn't appear that it is going to recover," said Mark Serreze of the National Snow and Ice Data Center in Colorado.
Global warming is so far having its most dramatic effects in the North, so Arctic sea ice is considered to be among the most important indicators of climate change.
Ice plays an vital role in global climate because it affects the delicate balance of ocean salinity and temperature. And it's crucial for everything from polar bears, who depend on the floe edge for their hunting, to shippers on the lookout for more efficient routes between ports.
Dr. Serreze's group uses data from satellites and weather stations to monitor the Arctic ice cap. Every fall the centre releases a snapshot of what is called the sea ice minimum.
This year's minimum showed the fourth-lowest extent of sea ice on a single day in 29 years of satellite records. When the entire month of September was considered, the amount of ocean either ice-covered or ice-choked was the second-lowest on record. Only 2005 was lower.
The study also found that the ice is melting faster than ever.
From 1979 to 2001, Arctic ice shrunk at the rate of 6.5 per cent a decade. After 2002, that pace rose to 7.3 per cent. By last year, the world was losing about 8 per cent of its ice each decade. Now the speed is 8.6 per cent.
The accelerating rate conforms to what scientists call feedback loops. Dark, open seas absorb the sunlight that white ice would have reflected, so warming speeds up the more ice melts. Also, open seas generate more cloud cover, blanketing the ocean during long Arctic winters and preventing temperatures from falling to normal levels.
"I'm not terribly optimistic about the future of the ice," Dr. Serreze said. If trends hold, Arctic ice will be largely gone by 2060 -- a decade earlier than the most pessimistic previous predictions, he said.
Most of the ice losses are concentrated off Russia's Siberian coast.
Winds and currents push ice into Canada's High Arctic islands, so coverage there is shrinking at only 1.6 per cent per a decade, said John Falkingham, chief forecaster for the Canadian Ice Service.
"We expect that the last ice that will remain in the Arctic Ocean will be in Canadian waters," he said. "The Northwest Passage will be the last place the ice will melt out of."
