By Ashley Hall
ABC News Online, 16 December 2010
A new study by US researchers has found polar bears could be saved from likely extinction if the world makes rapid and large cuts to carbon emissions.
It is an about-face from earlier research which suggested emissions were already too high for them to survive.
"The difference is that in the 2007 studies our model outcomes were based entirely on the assumption we would continue on the greenhouse gas emissions task we had followed for the last several years," said Dr Steve Amstrup, scientist emeritus with the US Geological Survey.
Both studies were led by Dr Amstrup, who is also the senior scientist for the conservation organisation Polar Bears International.
He says three years ago there was no suggestion that anybody was prepared to do anything to reduce greenhouse gas emissions.
"What we've done now and what we didn't do then is considered what effect reducing greenhouse gas emissions substantially would have on ice habitats and on polar bears," he said.
"And in fact there's one major publication we cite in our paper that predicted that we had already emitted enough greenhouse gases in the atmosphere to cause the Earth to warm enough that it would be beyond the tipping point."
But Dr Amstrup's team now believes there are mechanisms at play that put paid to the tipping point analysis.
"This is an important finding because if there were these tipping points, it might mean greenhouse gas mitigation efforts that we would do in the future might not be able to confer any conservation benefit," he said.
Dr Amstrup argues we need to take drastic action quickly if we want to preserve the habitat and the polar bears.
"Indeed the emissions trajectories we tested that had the best and most benefit to polar bears and their habitats were very aggressive mitigation scenarios," he said.
The size of cut he is talking about is much bigger than even the most ambitious targets mooted at the recent international climate change talks in Cancun.
"It's important to recognise the savings of polar bears, taking the actions we describe to preserve a more secure future for polar bears, have ramifications for the rest of the world," Dr Amstrup said.
In a separate study in Nature, researchers outline their concerns that the shrinking Arctic ice may lead to the extinction of polar bears no matter what emission cuts are achieved.
As marine mammals move into newly freed-up areas, they are increasingly inter-breeding.
In 2006 a hunter shot a polar bear with brown fur thought to be a crossbreed between a polar bear and a grizzly bear.
"And a second one was shot in 2010 and in this case, again it was a hybrid. In this case the DNA results indicated the mother of the hybrid was herself a hybrid," Dr Amstrup said.
Brendan Kelly, a research scientist with the US National Marine Mammal Laboratory, says his team has identified 34 examples of where crossbreeds have emerged.
"If you have a population [that] is reduced for whatever reason and it starts interbreeding with a more numerous species, then you have a real potential there to lose the rare species," he said.
"So sometimes this kind of breeding is sort of a final death knell of a depleted species."
Dr Kelly says the first breed likely to disappear from the Arctic thanks to crossbreeding is the North Pacific right whale, which has begun breeding with the bowhead whale.
It is thought there are only about 200 of them left.