Such a change would threaten coastal cities, change growing patterns for vegetation and destroy habitats for some wildlife, but an energy-starved world would have new areas for oil and gas exploration, according to the Arctic Climate Impact Assessment report.

The Arctic region, particularly offshore, has huge oil and gas reserves, mostly in Russia, Canada, Alaska, Greenland and Norway.

Warmer temperatures would make it easier to drill and ship oil from the Arctic, the report said. It did not attempt to quantify the costs of drilling and shipping Arctic oil and gas, or estimate how high energy prices would have to be to justify drilling in the region.

"Offshore oil exploration and production are likely to benefit from less extensive and thinner sea ice, although equipment will have to be designed to withstand increased wave forces and ice movement," the report said.

However, land access to energy reserves would likely be restricted due to a shorter season during which the ground is frozen hard enough to support heavy drilling equipment.

"The thawing of permafrost, on which buildings, pipelines, airfields and coastal installations supporting oil and gas development are located, is very likely to adversely affect these structures and increase the cost of maintaining them," the report said.

Energy companies would find it easier to transport oil and gas because the warmer temperatures would open sea routes.

"By the end of this century, the length of the navigation season...along the Northern Sea route is projected to increase to about 120 days from the current 20-30 days," the report said.

However, a longer shipping season will increase the risk of oil spills, the report warned.

The report was commissioned by the United States, Canada, Russia, Denmark, Iceland, Sweden, Norway and Finland. It concluded that global warming is heating the Arctic almost twice as quickly as the rest of the planet in a thaw that threatens millions of livelihoods.