The dramatic loss of sea ice across the Arctic was a major reason polar bears were listed as threatened under the Endangered Species Act nearly three years ago. Supremely adapted to life as marine predators, polar bears thrive only when they can travel, den and hunt for seals across the continent-size habitat created by the frozen polar sea.
At the time, scientists warned that global warming may have already "tipped" this ice cap into a precipitous and irreversible decline that would almost certainly drive polar bears to extinction. But polar bears may not be doomed after all. In a study published this week in Nature, a team of scientists ran computer models that predict ice will wax and wane in sync with global temperatures and will not suddenly disappear in the summer after it shrinks past some critical threshold.
Hold on: There's a caveat.
People must significantly reduce greenhouse gas emissions during the next two decades if they want to preserve enough Arctic sea ice for the Arctic's iconic top predator to survive the annual summer reduction in its habitat, according to a team of bear and atmospheric scientists, including former federal biologist Steve Amstrup, who studied Alaska's polar bears across three decades as a researcher for the U.S. Geological Survey in Anchorage.
Otherwise, the decline may continue as predicted.
Still, the lack of an irreversible "tipping point" in ice loss means that it's not too late for people to preserve the polar bear's frozen habitat and avoid losing the species, Amstrup told an international press teleconference in London on Tuesday.
"Conserving polar bears appears to be largely a matter of minimizing temperature rise," he said.
Arctic 'melting pot' indeed
The findings come as another group of researchers warn that polar bears and several other Arctic species may also face survival threats for a much different reason.
One brought on by their seeking solace, so to speak, with other Arctic critters. Interbreeding between species -- almost always limited to animals held in captivity - has been increasing throughout the Far North, according to a commentary titled "The Arctic Melting Pot," published in the same issue of Nature.
There have been at least two confirmed polar bear-grizzly bear hybrids in recent years -- plus crosses between beluga and narwhal, a right whale and bowhead, and more than 30 other possible combinations, wrote Alaska biologist Brendan Kelly and two co-authors.
There's nothing titillating about it.
"Rapidly melting Arctic sea ice imperils species through interbreeding as well as through habitat loss," they said. "As more isolated populations and species come into contact, they will mate, hybrids will form and rare species are likely to go extinct."