Most of the polar bears 'will be wiped out by end of the century'

By then, scientists say, global warming will have melted 42 per cent of the Arctic sea ice which the bears need to hunt and breed.

And by 2100, the experts warn, only a handful of the magnificent creatures will be left.

The report has been produced by the U.S. Geological Survey.

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In danger: Two polar bears perch on top of a melting remnant of ice, off the northern coast of Alaska

The scientists have publicised their findings in the hope of influencing U.S. Interior Secretary Dirk Kempthorne, who has been asked to put polar bears on the U.S. endangered species list.

Polar bears depend on floating sea ice as a platform for hunting seals, their main food. But the ice is disappearing throughout the Arctic because of climate change.

The team of American and Canadian scientists spent six months studying three groups of bears, on the ground, from spotter planes and in the lab, using sophisticated computer models.

Some team members fear the outlook is even bleaker for the bears than their report says.

They say the Arctic is warming faster than anywhere in the world and much faster than their computers had been forecasting.

Satellite observations have revealed that the ice has shrunk to an all-time low.

It is expected to retreat further this month, raising fears that it has reached a "tipping point" when melting will become irreversible.

Dr Mark Serreze, of the U.S. National Snow and Ice Data Centre, said: "The ice is in a death spiral. Two years ago I expected the Arctic to lose all its ice by the end of the century. Now I think it will be gone by 2030."

Without enough ice, polar bears would be forced on to land, where they are inefficient hunters, and would be unlikely to adapt in time.

Experts say few cubs would survive and the stress could make many females sterile.

Greenland and Norway have the largest bear populations, while a quarter live in Alaska and travel to Canada and Russia. But the Geological Survey says their range will shrink.

The Swiss-based World Conservation Union puts the Arctic polar bear population at between 20,000 and 25,000.

It says about 16,000 will disappear by 2050.

Some could survive longer in the far north, but many of those will have vanished by 2100, said Mr Amstrup.

Not everyone in the scientific community is convinced that global warming is happening on such an alarming scale, however.

Another investigation has found that polar bears are still being hunted by wealthy "sportsmen" who want their skins and heads as trophies.

The hunters are mostly Americans, Canadians and Russians, who pay up to £17,000 a trip.

At least ten internet companies offer bear-hunting safaris.

Most use native guides and dog sleds to chase bears until they are exhausted and make an easy target.

In Russia, poaching is a major problem with polar bear rugs selling for up to £5,000.

In Canada, the U.S. and Greenland, local people can kill a limited number of bears for food.