The drop in numbers will reduce the world population of the bears from around 26,000 to 17,000.

Researchers put the probability off a steep fall of around 30 per cent over the next three generations of bears at 71 per cent.

The researchers put the time frame of between 35 and 41 years.

The findings are consistent with polar bears being listed as ‘vulnerable’ on the International Union for Conservation of Nature (IUCN) red list of threatened and endangered species.

Loss of sea ice due to climate change has a direct impact on the ability of polar bears to feed and survive.

The bears need platforms of ice to reach their prey of ringed and bearded seals. Some sea ice lies over more productive hunting areas than others.

Scientists have divided polar bears into 19 sub-populations, two of which have already experienced population declines due to shrinking sea ice.

Others have shown signs of ‘nutritional stress’ or are currently said to be ‘stable’ or ‘productive’, according to the study authors.

The researchers combined polar bear generational length with sea ice projections based on satellite data and computer simulations.

They worked out the probability that reductions in the mean global population size of polar bears will be greater than 30 per cent, 50 per cent and 80 per cent in the space of three generations.

While the likelihood of a more than 30 per cent loss was high, there was little chance of populations crashing to near-extinction levels.

Writing in the Royal Society journal Biology Letters, the team, led by Dr Eric Regehr from the US Fish and Wildlife Service, concluded: ‘Our findings support the potential for large declines in polar bear numbers owing to sea ice loss.’

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