LONDON: Ice at the North Pole has melted to the lowest level since satellite observations began in 1972, meaning the Arctic is almost certainly the smallest it has been for 8000 years, polar scientists said.
If the trend continues, the Arctic will be largely ice-free in the northern summer 40 years earlier than anticipated in the last Intergovernmental Panel on Climate Change assessment report.
Daily satellite sea ice maps released by Bremen University physicists show that with a week's further 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 square kilometres on September 17, 2007.
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The National Snow and Ice Data Centre in the US 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,'' the head of the Institute of Environmental Physics at Bremen, Georg Heygster, said.
''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.''
The albedo effect is related to a surface's reflecting power - sea ice reflects more of the sun's heat back into space than darker seawater, which absorbs the sun's heat and gets warmer.
A senior researcher at the Australian Antarctic Division, Tony Worby, said the consensus view among polar scientists was that the Arctic melt was happening faster than the models used by the IPCC predicted.
''Some of the climate models showed that the ice would disappear in summer in about 70 years, but the observations are tracking well ahead of that,'' Dr Worby said.
Separate research suggests Arctic ice is in a downward spiral, declining in area and also thinning. Scientists at the Polar Science Centre of the University of Washington, Seattle, said last week that Arctic sea ice volume hit its lowest 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 half the average and 62 per cent lower than the maximum covering the Arctic in 1979. The research will be published in 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,'' the University of Washington senior oceanographer, Axel Schweiger, said.
The last time the Arctic was uncontestably free of summer-time ice was 125,000 years ago, at the height of the last major interglacial period.
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 Northwest and Northeast passages were mostly ice free, as they have been twice since 2008.
Last month, the 74,000-tonne STI Heritage tanker passed through the Northeast 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.