UW Adjunct Professor Helps Quantify Impact of Emissions on Polar Bears

In a new paper, scientists with Polar Bears International, the University of Wyoming and the University of Washington have, for the first time, quantified a direct link between greenhouse gas emissions and polar bear survival.

Published today (Thursday) in the journal Science, the report provides a template for estimating the demographic impact of proposed greenhouse gas-emitting actions on polar bears -- addressing a loophole in the Endangered Species Act that has historically blocked climate considerations.

The approach outlined in the paper connects the dots between greenhouse gas emissions, the number of ice-free days caused by specific amounts of emissions, and polar bear survival rates. It also explains the recent declining trends observed in some polar bear subpopulations.

Although polar bears were listed under the Endangered Species Act in 2008 because of sea ice loss caused by climate warming, then-Solicitor of the Department of the Interior David Bernhardt issued a legal opinion stating that greenhouse gas emissions would not be considered in reviews conducted under the act unless the impact of emissions from proposed projects could be separated from the impact of all historic global emissions. The inability to make that separation and measure the impact of a specific project meant that climate change was blocked from inclusion in Endangered Species Act evaluations.

“We’ve known for decades that continued warming and sea ice loss ultimately can only result in reduced distribution and abundance of polar bears,” says lead author Steven Amstrup, chief scientist emeritus at Polar Bears International and an adjunct professor at the University of Wyoming. “But, until now, we’ve lacked the ability to distinguish impacts of greenhouse gases emitted by particular activities from the impacts of historic cumulative emissions. In this paper, we reveal a direct link between anthropogenic greenhouse gas emissions and cub survival rates. The methodology, for the first time, allows us to parse the impact of emissions by source.”

Building on the foundation established in a 2020 report linking projected polar bear survival to summer fasting duration caused by global warming, the new paper -- whose other author is University of Washington Professor Cecilia Bitz -- takes the additional step of quantifying the number of ice-free/fasting days caused by a specific amount of carbon dioxide emissions. This allows for a direct calculation of the impact of a project’s emissions on future polar bear cub recruitment.

“When polar bears were listed as threatened in 2007, we talked about global warming and the risk of losing this iconic ambassador of the Arctic. Today, over 15 years later, my colleagues Amstrup and Bitz show unequivocally that those perceived risks are real,” says Merav Ben-David, a wildlife ecology professor at the University of Wyoming who has been studying polar bears with Amstrup for over 20 years but was not involved in the current project. “They show that polar bear reproductive failure is tied to greenhouse gas emissions. At a time when people die from the effects of extreme climate events, we may have forgotten the plight of polar bears. But we shouldn’t.”

The authors say their report addresses Bernhardt’s opinion and creates a direct link between emissions from individual projects and impacts on protected species. This gives the Department of the Interior the scientific basis to rescind the Bernhardt opinion and start including greenhouse gas emissions in reviews of all new projects it considers, they say.

“Overcoming the challenge of the Bernhardt opinion is absolutely in the realm of climate research,” Bitz says. “When the memo was written in 2008, we could not say how greenhouse gas emissions equated to a decline in polar bear populations. But, within a few years, we could directly relate the quantity of emissions to climate warming and later to Arctic sea ice loss as well. Our study shows that not only sea ice, but polar bear survival, can be directly related to greenhouse gas emissions.”

About Polar Bears International

Polar Bears International’s mission is to conserve polar bears and the sea ice they depend on. It also works to inspire people to care about the Arctic, the threats to its future and the connection between this remote region and the global climate. Polar Bears International is the only nonprofit organization dedicated solely to wild polar bears and Arctic sea ice, and the staff includes scientists who study wild polar bears. For more information, visit www.polarbearsinternational.org.