Arctic sea ice has shrunk to its lowest levels since record keeping began nearly 30 years ago, reaching a minimum area last weekend that was over a million square kilometres less than the previous low, scientists said Thursday.

After a summer in which satellites have been recording record lows in Arctic sea ice coverage, scientists from the University of Colorado at Boulder's National Snow and Ice Data Center said sea ice extent appears to have reached its minimum on Sept. 16, with the chances of it reaching a lower level unlikely in 2007.

'The amount of ice loss this year absolutely stunned us, because it didn't just beat all previous records, it completely shattered them.' —Scientist Mark Serreze

On that day, the Arctic sea ice extent stood at 4.13 million square kilometres.

Sea ice extent is the total area of all Arctic regions where ice covers at least 15 per cent of the ocean surface.

The record low breaks the previous mark from 2005 by about 1.2 million square kilometres — or slightly more than the size of the Northwest Territories.

The new low is also about 2.6 million square kilometres — or roughly twice the size of all of Quebec — less than the long-term minimum average from 1979 to 2000.

"The amount of ice loss this year absolutely stunned us, because it didn't just beat all previous records, it completely shattered them," said the University of Colorado at Boulder's senior scientist Mark Serreze.

Arctic sea ice generally reaches its minimum extent in September and its maximum in March.

Scientists are blaming the decline in Arctic sea ice on rising concentrations of greenhouse gases that have elevated temperatures from one to four degrees, as well as strong natural variability in Arctic sea ice, the researcher said.

The polar regions are a concern to climate specialists studying global warming because those regions are expected to feel the impact of climate change sooner and to a greater extent than other areas.

Sea ice in the Arctic helps keep those regions cool by reflecting sunlight that might otherwise be absorbed by darker ocean or land surfaces.

Last week the European Space Agency reported that Arctic sea ice coverage had shrunk enough to open the most direct route through the Northwest Passage.