ANCHORAGE, Alaska All is not lost for the polar bear, despite the rapid melt of Arctic sea ice that they need to survive, researchers reported on Wednesday.
Contrary to pessimistic assertions that polar bears are doomed because summer sea ice has melted past the point of no return, a new study concludes that significant curbs in carbon emissions would effectively cool the planet, rebuild ice and save the Arctic habitat and the bears in it.
"This is very much scientific evidence that there is hope," said Steve Amstrup, a retired U.S. Geological Survey polar bear expert who led the study published in the journal Nature.
"If people think that there's nothing they can do, they will do nothing. Here we've demonstrated that we can conserve polar bears. If we can do that, it has much broader ramifications."
Polar bears have become a symbol of climate change fears because they depend on vast stretches of year-round sea ice that has become scarce in summer and fall months.
Warming trends are amplified in the polar regions, largely because of a self-reinforcing "albedo" effect that accelerates the impacts of solar heat as reflective white snow and ice are replaced by dark water surfaces and landscapes.
Amstrup was part of the USGS team that concluded in 2007 that two-thirds of the world's 22,000 polar bears -- including all those in Alaska -- would likely vanish by mid-century if current carbon and warming trends continued.
While that prediction remains valid, the new study found that ice conditions have not gotten so bad that they cannot be repaired, Amstrup said in a telephone interview.
"Our results seem to be pretty conclusive that there doesn't seem to be a tipping point in summer sea ice," said Amstrup, now at the Montana-based conservation organization Polar Bears International.
Amstrup's team used mathematical models, checked against real-world data about polar bear populations and summer Arctic ice trends, for their report.
They also considered the slight rebuilding of summer ice pack after 2007, the year ice coverage reached its lowest point since satellite records began in 1979.
"What we projected in 2007 was based solely on the business-as-usual greenhouse gas scenario," Amstrup said.
For a scenario in which polar bear populations are likely to remain in place through the century, the study assumes global atmospheric carbon levels stabilizing at 450 parts per million.
Currently, atmospheric carbon levels are at about 388 parts per million, according to the most recent information from the National Oceanic and Atmospheric Administration's Mauna Loa Observatory in Hawaii.
Under present trends, atmospheric carbon levels are expected to reach or exceed 700 parts per million by the end of the century.
Ensuring that global carbon levels are no more than 450 parts per million by century's end would require aggressive actions, said one environmentalist involved in climate and polar-bear conservation issues.
"It's very daunting, but within the realm of possibility," said Brendan Cummings, senior counsel for the Center for Biological Diversity.
(Editing by Maggie Fox and Mohammad Zargham)