The survey, being presented at a four-day conference in Iceland lasting until Friday, projects the Northern Sea Route along the coast of Russia is likely to be navigable for 120 days a year in 2100 against just 30 in 2000 as ice recedes.

It says the Arctic Ocean could be almost ice-free in summer by 2100 and that a build-up of heat-trapping gases in the atmosphere from burning fossil fuels is heating the Arctic twice as fast as the rest of the globe.

Yet the routes between the Pacific and Atlantic oceans, an icy graveyard for explorers in past centuries, are unlikely to spur a shipping rush. As the ice melts there may be more icebergs, and even more fog.

"Greater use of the transpolar routes isn't going to happen quickly because there are too many uncertainties," said Walter Parker, chairman of the Circumpolar Infrastructure Task Force of the Arctic Council.

"Bankers are not interested in lending unless governments also get involved in funding," he said. "Major shippers are not interested yet." The Arctic Council groups the United States, Russia, Canada, Finland, Sweden, Norway, Iceland and Denmark.

FAR FROM TERRORISM

In the long term, the United States and other nations might find the remote routes a safer alternative to more southerly routes where terrorism or piracy could be growing risks. Cargoes like nuclear waste might be transported via the Arctic.

"Maybe these (Arctic) routes will be used because other routes have security issues," said Lawson Brigham, deputy director of the U.S. Arctic Research Commission. "Maybe terrorists don't like the cold."

The United States now has no ice-hardened warships except for nuclear submarines that can smash through ice to surface.

The polar route has clear attractions for shippers - from Osaka, Japan, to Rotterdam, the Netherlands, a trip around the polar sea could save about two weeks on a 45-day voyage through the Suez or Panama Canals. Yet the Arctic report also says a thaw may add complexities. The Northwest Passage through a maze of islands north of Canada, for instance, might become more clogged by icebergs if ice bridges blocking northern channels thaw out.

The report, by 250 scientists, says the Arctic is warming faster than the rest of the planet partly because darker ground and water, once uncovered, soak up more heat than snow and ice.

Brigham said the polar region was already used for shipping - 52 vessels have blasted their way to the North Pole with a Soviet nuclear-powered icebreaker the first in 1977.

Global warming's main benefit for shipping, he said, would be to help transport minerals like nickel from Russia, zinc from Alaska or oil and gas from future Arctic fields. Fishing vessels or cruise ships could also get easier access.

But governments would face huge problems of how to rescue crews in case of accidents, or how to clean up oil spills.

"The Arctic could be a new Wild West," said Samantha Smith, director of the WWF conservation group's Arctic Program. "When the ice melts there will be a huge value in opening the region to shipping. We're afraid it will be done without regulation."