The act requires agencies to ensure projects they approve don’t further harm listed species. But a 2008 Department of Interior legal opinion said greenhouse gas emissions didn’t have to be considered because the impact from specific projects couldn’t be distinguished from that of all historic global emissions.
Polar bears, which occur in 19 subpopulations throughout the Arctic, rely on sea ice to hunt for seals. As ice melts, they either end up on land or must swim farther from shore to find ice, which hurts their ability to find food and leads to long periods of fasting that deplete fat reserves.
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. “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.
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.