A polar bear cub and sow newly emerged from their den along the Arctic Coast of Alaska. Photo: Steven Kazlowski/Barcroft Media/Getty Images

The loss of sea ice due to climate change is predicted to threaten the survival of polar bear populations across the Arctic by the end of the century, new research shows.

Why it matters: "Polar bears have long been considered messengers of the climate change symptoms that will impact all life, including humans," says Polar Bears International chief scientist Steven Amstrup.

"The impacts could occur earlier — and in fact in Alaska, they already are occurring earlier than what we’ve projected."
— Steven Amstrup of Polar Bears International

What's new: The new study, co-authored by Amstrup and published in the journal Nature Climate Change Monday, marks the first time scientists have been able to predict when, where and how polar bears are likely to vanish. Previous models didn't account for the different Arctic living conditions and levels of sea ice subpopulations encounter.

  • University of Wyoming professor Merav Ben-David, who has studied polar bears with Amstrup for 20 years but wasn't involved in this paper, said the modeling would be an essential conservation tool.
GIF: Polar Bears International

Background: Polar bears depend on sea ice to hunt prey. The ice is disappearing in regions such as Alaska, which last year saw unprecedented ice loss in the Bering Sea and a rapid reduction in the Chukchi and Beaufort seas.

  • Scientists first recognized significant changes in Arctic sea ice in the late 1990s, Ben-David said. "Since then, we have started seeing effects of climate change on polar bears."
  • Females can breed without the ice. But with limited access to food, Ben-David said they lack nutrients to feed cubs and energy to hunt — leaving them "unable to nourish them and raise them into adulthood."

What they did: "By estimating how thin and how fat polar bears can be, and modeling their energy use, we were able to calculate the threshold number of days that polar bears can fast before cub and/or adult survival rates begin to decline," study author Péter Molnár of the University of Toronto Scarborough said in a statement.

  • The paper explores what's in store for polar bears under two different greenhouse gas emissions scenarios.
  • Under a moderate emissions scenario (known as "representative concentration pathway 4.5"), they found polar bears in the Laptev Sea, north of Russia, and the northern Beaufort Sea, north of Alaska, would face "possible" reproductive collapse by 2080. Subpopulations elsewhere would also be threatened.
  • Under a very high emissions growth scenario (RCP 8.5), Canada's Queen Elizabeth Islands "may be the only place that polar bears could continue to thrive" by 2080, Amstrup said.
  • Other subpopulations would face some threat level of reproductive failure — with this outcome "inevitable" for those in the Barents Sea, between Russia and Norway, and Canada's Southern Hudson Bay.

Yes, but: Some researchers believe that scenario is unlikely because the cost of low-carbon technologies is falling and global coal use may be as well.

  • Amstrup said it is important to consider, though, as some leaders are still pushing for fossil fuel use and "we have yet to see much change in the rate of increase in CO2 concentrations."

What to watch: Movements like the 2019 climate strikes have motivated governments to act, with several European countries pledging big cuts and some coronavirus bailouts containing green conditions, says New Zealand Centre for Planetary Ecology climate scientist Robert McLachlan.

  • These could help to mitigate the threat to polar bear populations.

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