Scientists say study found a direct link between greenhouse gas emissions and polar bear survival

Researchers estimated the relationship between how long bears fasted and each gigaton of cumulative emissions, which they said allowed them to calculate the impact of emissions from specific projects on future polar bear cub survival.

“It’s basically connecting the dots” from emissions to ice-free days to impacts on polar bears, said Amstrup, who believes the method can be applied to many other species, such as sea turtles or coral reefs. He also believes the study makes a case for rescinding the 2008 opinion barring climate considerations, because the Endangered Species Act requires federal agencies to use the best available scientific data.

Interior officials could not be reached immediately for comment.

Todd Atwood, a wildlife biologist who leads the US Geological Survey’s polar bear research programme and was not involved in the study, said it is an important initial step in quantifying the relationship between greenhouse gas emissions and polar bear survival, and “is successful in the sense that it provides a framework for beginning to do that”.

But the lack of consistent estimates of population trends and survival rates for some polar bear subpopulations, which are distributed over a very large geographic area with differences in sea ice and food sources, can be “problematic when you’re trying to to match for recent greenhouse gas emission trajectories with population survival rates”, he said.

“This is not a critique of them, but … there’s a lot of subpopulations that are really hard to get to,” he said, adding that there’s not enough funding to do that.

Another expert believes the study shows a correlation between emissions and polar bear cub survival, but not a direct cause and effect.

“I think it takes us a little bit closer to understanding some of those relationships, but … I just don’t know that this paper pushes it over a new threshold,” said Andrew Derocher, a polar bear expert and biological sciences professor at the University of Alberta, who believes polar bears are at risk of extinction long-term. “I just don’t think that this is the smoking gun that is going to change opinion.”

Dan Rohlf, a professor at Lewis and Clark Law School in Portland, Oregon, and an expert on the Endangered Species Act, said the study makes important advances in understanding the effects of cumulative emissions on polar bears.

“I completely agree with the authors that it’s essentially ludicrous that … we list polar bears as threatened because of climate change, and then we turn around and say we can’t consider the impacts of these federal actions that will increase greenhouse gas emissions,” Rohlf said. “It makes no sense whatsoever.”

But federal agencies will only consider emissions from one project at a time – each of which would have relatively small impacts – and won’t account for cumulative emissions of federal actions, Rohlf said.

Agencies such as the Fish and Wildlife Service have the authority to determine that polar bears already are in jeopardy and that greenhouse gas emissions should be reduced, Rohlf said. Project evaluations then could consider whether emissions are consistent with a goal of reducing greenhouse gases – but “it wouldn’t fly politically”.

”The whole theory (now) is you keep allowing incremental adverse effects until the last one sort of is the straw that breaks the camel’s back and then you have to stop,” he said. “Well, if the camel’s back is already broken, we’ve got to stop now. And I think that’s the situation that we’re in for polar bears.”