New study establishes link between greenhouse gases and polar bear survival

A study says scientists for the first time are able to directly quantify the impact of human-caused greenhouse gas emissions from specific sources on polar bear cub survival

Fifteen years after polar bears were listed as threatened, a new study says researchers have overcome a roadblock in the Endangered Species Act that prevented the federal government from considering climate change when evaluating impacts of projects such as oil and gas drilling.

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.

A study published Thursday in Science’s Policy Forum says scientists for the first time are able to directly quantify the impact of human-caused greenhouse gas emissions from specific sources on polar bear cub survival.

It “just seems odd" that polar bears were listed because of the loss of sea ice due to global warming “but emissions have not been considered,” said lead author Steven C. Amstrup, chief scientist emeritus at Polar Bears International and a professor at the University of Wyoming.

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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. Human-caused global warming means there are fewer days of sea ice to help build up those reserves and longer fasting periods, and scientists have said most polar bears could become extinct by the end of the century unless warming is curbed.

A 2020 study found the number of fasting days, determined by the number of ice-free days every summer, directly affected cub survival. The new study, authors said, took that a step further and quantified the number of ice-free, fasting days caused by a specific amount of human-caused greenhouse gas emissions — distinct from what's already in the atmosphere.