Anchorage (Alaska): An analysis of 20 years worth of real-life observations supports recent UN computer predictions that by 2050, summer sea ice off Alaska's north coast will probably shrink to nearly half the area it covered in the 1980s, US government scientists say. Such a loss could have profound effects on mammals dependent on the sea ice, such as polar bears, now being considered for threatened species status because of changes in habitat due to global warming. It could also threaten the catch of fishermen.

In the 1980s, sea ice receded 30 miles to 50 miles each summer off the north coast, said James Overland, a Seattle-based Oceanographer for the National Oceanic and Atmospheric Administration. "Now we are talking about 300 miles to 500 miles north of Alaska," he said of projections for 2050.

That is far past the edge of the highly productive waters over the relatively shallow continental shelf, considered important habitat for polar bears and their main prey, ringed seals, as well as other ice-dependent mammals, such as walrus. The researchers reviewed 20 computer scenarios of the effects of warming on sea ice, used by the United Nations Intergovernmental Panel on Climate Change in its assessment report released this year.

The researchers compared those models with observations from 1979 through 1999,Overland said and concluded that the summer ice in the Beaufort Sea likely will have diminished by 40 per cent, compared with its 1980s area.