"(The) Arctic climate is warming rapidly now and much larger changes are projected," according to the conclusions of the international study, compiled by 600 experts and due for release at a conference in Iceland in November.
Rising temperatures will disrupt life for people, bringing more storms and destabilizing everything from homes to oil pipelines. Melting glaciers could raise global sea levels and spoil habitats for creatures like polar bears, it says.
The Arctic is warming faster than the rest of the world partly because sea water and dark ground, once exposed, trap far more heat than ice and snow which reflect the sun's rays.
The report's draft summary, a copy of which was obtained by Reuters last week, says the rise in temperatures is being stoked by human emissions of greenhouse gases, mainly from burning fossil fuels in cars, factories and power plants.
Arctic temperatures could surge by 8 degrees to 14 degrees Fahrenheit - or roughly double the rate predicted by U.N. studies for the planet as a whole by 2100, it says.
But nations in the Arctic region - the United States, Russia, Canada and Nordic countries - are sharply divided about how to act on the scientists' conclusions, with Washington opposed to any major initiatives, diplomatic sources say.
U.S. OPPOSES CAPPING EMISSIONS
Nordic countries see the study as alarming evidence that the world should act to cap emissions of greenhouse gases like carbon dioxide from fossil fuels.
But President Bush is an opponent of caps and pulled out of the U.N.'s stalled Kyoto protocol in 2001, the main global plan for limiting emissions. He said Kyoto would be too costly and wrongly excluded developing nations.
Ministers from Arctic nations are to meet in Iceland in November, after the report is issued, to agree recommendations.
Among conclusions, the Arctic Climate Impact Assessment (ACIA) says the warming in the Arctic will "have worldwide implications."
Run-off from melting glaciers and the Greenland icecap could raise global sea levels and disrupt ocean circulation, it says. And biodiversity elsewhere could be affected because some migratory species breed in the Arctic.
The report also says "Arctic vegetation zones are projected to shift, bringing wide-ranging impacts" and that "Animal species' diversity, ranges and distributions will change, some dramatically."
Meanwhile, it says, many coastal communities and facilities face increasing exposure to storms.
And indigenous peoples would face major economic and cultural impacts, it says. Ultraviolet radiation - known to cause skin cancer and immune system disorders in humans - would also rise sharply.
The report also concludes that "reduced sea ice is very likely to increase marine transport and access to resources." The thaw could open short-cut shipping routes between the Atlantic and Pacific Oceans.
But on land, buildings, oil pipelines, industrial facilities, roads and airports could need substantial rebuilding if permafrost thaws, it says.