Figures from the National Snow and Ice Data Centre indicate six or seven- year low over past three decades
Juliette Jowit
guardian.co.uk, Wednesday 7 April 2010
The melting Arctic ice cap recovered slightly over the last winter, but scientists warned that it was still one of the worst years on record.
The twice yearly figures published by the National Snow and Ice Data Centre of the winter high and summer low for the Arctic sea ice is seen as a powerful indicator of global warming.
Last night the US organisation released the data for the winter of 2009-10 showing the maximum extent reached on 31 March was 5.89m square miles (15.25m sq km). This was 250,000 square miles (650,000 sq km) below the 1979 to 2000 average for March when measurements are taken for winter sea ice. The rate of decline for March over the 1978 to 2010 period is 2.6% per decade, according to NSIDC data. Arctic sea ice reflects sunlight, keeping the polar regions cool and moderating global climate.
NSIDC said there had been some recovery in the amount of ice that was two years old or more, from last year's previous record low.
However, the spread of the ice, though higher than in some recent very bad years, was still low compared to past decades. "I think it's the sixth or seventh lowest maximum out of the previous 32 years," said Walt Meier, a research scientist at NSIDC.
Looking ahead to the other key annual figure - the lowest extent of sea ice at the end of the summer melting season - Meier said this year was also expected to be historically low, depending on temperatures and winds which blow the ice around, and sometimes out of the Arctic Sea into the warmer Atlantic and Pacific currents.
"I would say [it's going to be] low, perhaps one of the lowest, but not approaching 2007," said Meier, referring to the record lows that year when the Arctic lost an area of ice the size of Alaska in one year. "Given the amount of thin ice we know we're going to be low, it's just a matter of how low."
Last month, Japanese scientists reported in the journal Geophysical Research Letters that winds rather than climate change had been responsible for around one-third of the steep downward trend in sea ice extent in the region since 1979. The study did not question global warming is also melting ice in the Arctic, but it could raise doubts about high-profile claims that the region has passed a climate "tipping point" that could see ice loss sharply accelerate in coming years.
Last week the Catlin Arctic Survey leader Ann Daniels wrote for the Guardian about the ice seen by the team of three explorers trekking across the Arctic in "incredibly strong north winds" to measure ocean acidification linked to greenhouse gases. "We've also been seeing vast areas of open water and very thin ice — it's the first time any of us have experienced anything quite like this on such a large scale," wrote Daniels. "The way the ice is behaving is simply the strangest we have ever seen."
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