The north-west passage was, again, free of ice this summer and the polar region could be unfrozen in just 30 years.

Arctic sea ice has melted to a level not recorded since satellite observations started in 1972 — and almost certainly not experienced for at least 8,000 years, say polar scientists.

Daily satellite sea-ice maps released by Bremen university physicists show that with a week's more melt expected this year, the floating ice in the Arctic covered 4.24 million square kilometres on September 8. The previous one-day minimum was 4.27 million sq.km. on September 17, 2007.

The U.S. National Snow and Ice Data Centre (NSIDC), in Colorado, is expected to announce similar results in a few days.

The German researchers said the record melt was undoubtedly because of human-induced global warming. “The sea-ice retreat can no more be explained with the natural variability ... caused by weather,” said Georg Heygster, head of the Institute of Environmental Physics at Bremen.

“Climate models show that the reduction is related to the man-made global warming, which, due to the albedo effect, is particularly pronounced in the Arctic,” he said. The albedo effect is related to a surface's reflecting power — whiter sea ice reflects more of the sun's heat back into space than darker seawater, which absorbs the sun's heat and gets warmer.

Floating Arctic sea ice naturally melts and re-freezes annually, but the speed of change has shocked scientists — it is now twice as great as it was in 1972, according to the NSIDC. Arctic temperatures have risen more than twice as fast as the global average over the past half century.

Separate research suggests that Arctic ice is in a downward spiral, declining in area but also thinning. Scientists at the Polar Science Centre of the University of Washington, Seattle, said last week that Arctic sea—ice volume was at its lowest ever level in 2010 and was on course to set more records this year. Their data suggests that the volume of sea ice last month was about 2,135 cubic miles — half the average and 62 per cent lower than the maximum covering the Arctic in 1979. The research will be published in a forthcoming issue of the Journal of Geophysical Research.

“Ice volume is now plunging faster than it did at the same time last year when the record was set,” said Axel Schweiger.

If current trends continue, a largely ice-free Arctic in the summer months is likely within 30 years — that is 40 years earlier than anticipated in the last Intergovernmental Panel on Climate Change (IPCC) assessment report. The last time the Arctic was uncontestably free of summertime ice was 125,000 years ago, at the height of the last major interglacial period.

“This stunning loss of Arctic sea ice is yet another wake-up call that climate change is here now and is having devastating effects,” Shaye Wolf, climate science director at the Centre for Biological Diversity in San Francisco told journalists.

Arctic ice plays a critical role in regulating Earth's climate. Retreating summer sea ice is described by scientists as a measure and a driver of global warming. This year, the north-west and north-east passages were mostly ice free, as they have been twice since 2008. In August, the 74,000-tonne STI Heritage tanker passed through the north-east passage in just eight days on its way from Houston, Texas, to Thailand. The north-east sea route, which links the Atlantic to the Pacific, is likely to become a ship operator's favourite.

Further evidence of dramatic change in the Arctic came last week from Alan Hubbard, a Welsh glaciologist at Aberystwyth University, who has been studying the Petermann glacier in northern Greenland. The glacier, which covers about 6 per cent of the icecap, is 300 km long and up to one km high. In August last year, a 260 sq.km. block of ice calved from the glacier. Pictures show that by July it had melted and disappeared.

“I was gobsmacked. It [was] like looking into the Grand Canyon full of ice and coming back two years later to find it full of water,” said Mr. Hubbard.

Last year (2010) tied with 2005 as the warmest year on record. — © Guardian Newspapers Limited, 2011

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