40% of Arctic ice cap will be gone by midcentury, Seattle scientists say

Global warming will shrink the Arctic ice cap much faster than previously expected, Seattle scientists reported today.

About 40 percent of the ice that usually blankets the top of the world during the summer will be gone by 2050, according to a new analysis. Earlier studies had predicted it would be nearly a century before that much ice vanished.

"This is a major change," said James Overland, an oceanographer at the National Oceanic and Atmospheric Administration's Pacific Marine Environmental Laboratory. "This is actually moving the threshold up."

The findings come in a year when the floating ice that usually covers much of the Arctic Ocean year-round has shrunk to the lowest levels ever recorded. This summer the normally ice-clogged Northwest Passage across the Canadian Arctic opened up completely for the first time.

Scientists blame the rapid melt on a combination of natural weather fluctuations and global warming. But over the next few decades, the effects of global warming will dominate in the region, Overland said. And because greenhouse gases linger in the atmosphere for up to five decades, the melting will intensify even if emissions from cars, power plants and industries are slashed dramatically.

"I'm afraid to say a lot of the impacts we're going to see in the next 30 to 40 years are pretty much already established," Overland said.

If 40 percent of Arctic sea ice is lost, polar bears, walruses and other ice-dependent species will be driven onto land or forced into a few remaining ice refuges.

Changes in the Arctic ecosystem would be bad news for whales that feed on small crustaceans and other cold-loving bottom-dwellers. But some fish, like pollock and salmon, could benefit from warmer, ice-free waters, Overland said.

"There will be winners and losers."

Overland and Muyin Wang, a meteorologist at NOAA's Joint Institute for the Study of the Atmosphere and Ocean at the University of Washington, analyzed the 20 national and international computer models used to predict climate change. They measured the computer predictions against actual ice measurements, and picked the 10 or so models that provided the best matches.

Then, they used those models to look ahead.

"We found with the remaining models that ... most of them lost over 40 percent of the ice area by 2050," Overland said. The study will be published in the Sept. 8 issue of Geophysical Research Letters.

The Intergovernmental Panel on Climate Change, an international science and policy group, reached a similar conclusion in a report issued earlier this year. But because the IPCC included all of the models — even those with lower accuracy — their prediction was shakier than the new analysis.

Earlier computer models had predicted significant ice loss wouldn't occur until 2100.

An international power struggle over the Arctic is already under way, as governments rush to stake claims on shipping lanes, oil deposits and mineral resources that will become accessible as the ice cover shrinks.

A Russian miniature submarine planted a flag on the sea bed under the North Pole this summer. Canada announced plans for military bases along the Northwest Passage, which it claims as sovereign territory. President Bush insists the route is an international passageway.

Sandi Doughton: 206-464-2491 or sdoughton@seattletimes.com