ANCHORAGE - Computer predictions of a dramatic decline of sea ice in regions of the Arctic are confirmed by actual observations, according to scientists for the National Oceanic and Atmospheric Administration.
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The Seattle-based researchers reviewed 20 computer scenarios of the affects of warming on sea ice used by the Intergovernmental Panel on Climate Change in its assessment report released this year.
The researchers compared those models with sea ice observations from 1979 through 1999, rejecting about half because they did not match what satellites showed, said oceanographer James Overland.
But using the most reliable models, the NOAA scientists reached the same unhappy conclusion: By 2050, summer sea ice in the Beaufort Sea off Alaska's north coast likely will have diminished by 40 percent compared to the 1980s. The same is likely for the East Siberian-Chukchi Sea region off northwest Alaska and Russia. In contrast, Canada's Baffin Bay and Labrador showed little predicted change.
There was less confidence for winter ice, but the models also predict a sea ice loss of more than 40 percent for the Bering Sea off Alaska's west coast, the Sea of Okhotsk east of Siberia and the Barents Sea north of Norway.
A 40 percent loss of summer sea ice off Alaska in the Beaufort Sea could have profound effects on marine mammals dependent on the sea ice such as polar bears, now under consideration by the U.S. Fish and Wildlife Service for "threatened" status under the Endangered Species Act because of changes in the animals' habitat from global warming.
Overland, an oceanographer at NOAA's Pacific Marine Environmental Laboratory in Seattle, and Muyin Wang, a meteorologist at NOAA's Joint Institute for the Study of the Atmosphere and Ocean at the University of Washington in Seattle, reviewed 20 computer models provided through the IPCC. Their research paper will be published Saturday in Geophysical Research Letters, a publication of the American Geophysical Union.
In the 1980s, sea ice receded 30 to 50 miles each summer off the north coast of Alaska, Overland said.
"Now we're talking about 300 to 500 miles north of Alaska," he said of projections for 2050.
That's far past the edge of the highly productive waters over the relatively shallow continental shelf off Alaska's north coast, considered important habitat for polar bears and their main prey, ringed seals, plus other ice-dependent mammals such as walrus.
Kassie Siegel of the Center for Biological Diversity, who wrote the petition seeking federal protection for polar bears, said NOAA's retrospective of sea ice projections does not even take into account sea ice figures for this summer recorded by the National Snow and Ice Data Center. As of Tuesday, the center's measurement of sea ice stood at 1.70 million square miles, far below the previous record low for summer ice of 2.05 million square miles recorded Sept. 20, 2005.
The situation is dire for polar bears, Siegel said.
"They're going to drown, they're going to starve, they're going to resort to cannibalism, they're going to become extinct," she said.
As ice recedes, many bears will get stuck on land in summer, where they have virtually no sustainable food source, Siegel said. Some will try and fail to swim to sea ice, she said. Bears that stay on sea ice will find water beyond the continental shelf to be less productive. Females trying to den on land in the fall will face a long swim.
"It's absolutely horrifying from the polar bear perspective," she said.
Less sea ice also will mean a changing ecosystem for commercial fishermen and marine mammals in the Bering Sea, Overland said.
With sea ice present, much of the nutrients produced in the ocean feed simple plankton that bloom and sink to the ocean floor, providing rich habitat for crabs, clams and the mammals that feed off them, including gray whales and walrus.
"If you don't have the ice around, the productivity stays up closer to the surface of the ocean," Overland said. "You actually have a change in the whole ecosystem from one that depends on the animals that live on the bottom to one that depends on the animals that live in the water column. So you have winners and losers."
That could mean short-term gains for salmon and pollock, he said. But it also could mean that fishermen will have to travel farther north to fish in Alaska's productive waters, and warm-water predators might move north.
Overland said sea ice computer models have performed well accounting for how ice melts from global warming and for the albedo effect _ accelerated warming due to the presence of dark water that absorbs most of the sun's radiation, warming the ocean and making it harder for water to freeze, in contrast to ice, which reflects most of the sun's radiation.
The models do not do as well accounting for wind and cloud patterns and other factors that may have contributed to recent warming, Overland said.
But the contribution to warming by greenhouse gas emissions likely are set, he said. Emissions stay in the atmosphere for 40 to 50 years before being absorbed by the ocean. The amount put out in the last 20 years and the carbon dioxide put out in the next 20 will be around to influence the half-century mark, Overland said.
"I'm afraid to say, a lot of the images we are going to see in the next 30 to 40 years are pretty much already established," he said.