Study quantifies link between greenhouse gases, polar bear survival

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When sea ice melts in summer, they retreat onto land or unproductive ice far from the shore, where they endure long stretches of fasting. These periods are growing longer as global temperatures rise.

A landmark paper published in Nature in 2020 was the first to calculate links between changes in the sea ice caused by climate and polar bear demographics.

Building on this work, Amstrup and Bitz established the mathematical relationships between greenhouse emissions and fasting days as well as cub survival, in 15 out of 19 of the polar bears’ subpopulations, between 1979 and 2020.

For example, the world currently emits 50 billion metric tons of carbon dioxide or equivalent gases into the atmosphere annually, and that is reducing the rate of cub survival by over three percentage points per year in the South Beaufort Sea subpopulation.

In healthy populations, cub survival during the first year of life is around 65 percent.

“You don’t have to knock that down very far before you don’t have enough cubs entering the next generation,” said Amstrup.

In addition, the paper provides US policy makers with the tools they need to quantify the impact of new fossil fuel projects slated to occur on public lands in the coming decades. 

It can also be applied retrospectively to understand the emissions from specific projects, companies or even countries in the past, to inform global negotiations about climate and biodiversity.

– Implications for other species –

While the pair are confident in their calculations, they say their work can be further refined by more ground research, for example better estimates of the mass of polar bears at the time they enter their fasting period.

Joel Berger, university chair of wildlife conservation at Colorado State University, praised the paper.

“Amstrup and Bitz render an incontrovertible quantitative link among greenhouse gas emissions, sea ice decline, fasting duration — a physiological response to lost hunting opportunities for seals — and subsequent polar bear demographics,” said Berger, who was not involved in the research.

Beyond providing a potential policy solution to the legal loophole, the new research could have implications that reach far beyond polar bears, second co-author Cecilia Bitz, a climatologist at the University of Washington, told AFP.

Methods laid out in the paper can be adapted for other species and habitats, such as coral reefs, or Florida’s Key deer. 

“I really hope this stimulates a lot of research,” Bitz said, adding she was already reaching out to new collaborators.

– by Issam Ahmed

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