Record Arctic ice melt causes alarm

Theage.au.co, September 22, 2007

Washington (Reuters): SEA ice over the Arctic has shrunk to its smallest known area, shattering a record set in 2005 and continuing a trend spurred by human-caused global warming, scientists say.

"It's really quite astounding," said Walt Meier, a research scientist at the US National Snow and Ice Data Centre. "It's the biggest drop from a previous record that we've ever had."

Sea ice freezes and melts seasonally, but never had it ebbed to this small a patch. Compared with 2005, this year there had been a decrease of more than 1 million square kilometres — nearly four times the size of Victoria — the centre said. It is more than double the decline between 2002 and 2005.

"That's a dramatic change in one year," Dr Meier said of this year's sea ice decrease.

"Certainly we've been on a downward trend for the past 30 years or so, but this is really accelerating the trend."

The minimum amount of ice occurred on Sunday and freezing has already begun in some places, according to satellite imagery used by the centre.

Melting sea ice, unlike the melting glaciers of Greenland and Antarctica, does not contribute to the global sea level rise, much as an ice cube in a glass of water does not make the level of liquid rise when it melts.

But without the bright white of sea ice to reflect the sun's rays, the Earth loses what some climate scientists call its air-conditioner. The less ice there is, the more dark water there is to absorb the warming solar radiation.

This year's record was caused by a "perfect storm" of interacting factors, Dr Meier said. These included a long-running high pressure system that kept skies cloudless over the Arctic, along with a circulation pattern that pushed ice out of the Arctic towards Greenland, instead of letting it circle around the Beaufort Sea north of Alaska.

While this year's ice minimum could not be directly attributed to anthropogenic — human-caused — global climate change, the trend that brought it about could, he said.

"This year, the reason why (the ice) was so low was not because there's more anthropogenically generated carbon dioxide dumped in the past year, it's because of this high pressure … but you can't really explain the overall trend without invoking anthropogenically global warming," Dr Meier said.

The decrease in Arctic sea ice was forecast in models used by the UN Intergovernmental Panel on Climate Change, which this year said with 90 per cent probability that global warming exists and that human activities contribute to it.