Greenhouse gas cuts 'could stop polar bear extinction'

Scientists said there was still hope for the iconic Arctic predator which three years ago appeared to be doomed by global warming.

Projections in 2007 indicated that by the middle of the century loss of Arctic ice would have reduced the 22,000 polar bear population by two thirds.

Eventually as temperatures rose it would be too late to prevent a catastrophic melting of sea ice, and the bears could vanish altogether.

The findings led to the polar bear being listed as a threatened species in 2008.

But the new research described in the journal Nature challenges the notion of a "tipping point" above which sea ice loss would be unstoppable.

The computer simulations, which now factor in relationships between polar bears and their environment, show there is still time to avert ecological disaster in the Arctic.

A "significant" reduction in greenhouse gas emissions that kept global warming below 1.25C by the end of the century could allow polar bear numbers to recover.

"Our research offers a very promising, hopeful message, but it's also an incentive for mitigating greenhouse gas emissions," said Dr Cecilia Bitz, one of the scientists from the University of Washington in Seattle, US.

Previous work by Dr Bitz and colleagues showed that unchecked temperature increases could lead to the loss of vast areas of Arctic ice in less than a decade.

Polar bears depend on sea ice to gain access to their primary food source, ringed and bearded seals.

During seasons when they cannot reach the ice the bears go hungry and can lose two pounds of body weight a day.

As the ice-free periods have increased, the animals have had to last longer without food.

The new computer model included features of polar bear life history and ways in which the predators interact with their environment.

It suggested that if emissions of greenhouse gases such as carbon dioxide were substantially reduced in the near future, rapid ice loss would be followed by the large scale retention of remaining ice.

Throughout the rest of this century there could also be a partial recovery of ice that had already disappeared.

With sufficient emission reductions in the next decade or two, enough Arctic ice was likely to remain intact during late summer and early autumn for polar bears to survive.

In 2007, there seemed a very high likelihood that polar bears would become extinct in at least two of the regions given the current pattern of greenhouse gas emissions.

Loss of Arctic sea ice also threatened polar bears and other species in another way, according to a second study published in Nature. It was encouraging cross-breeding that could push some species to extinction, it said.