Study identifies the relationship between carbon dioxide emissions and the decline in polar bear numbers | TV5MONDE

Polar bears have long been a symbol of the damage caused by climate change, which is melting the sea ice on which their survival depends.

But until now, the impact of a single coal-fired power plant on these iconic mammals has not been quantified.

A new study, published Thursday in the journal Science, shows that it is now possible to calculate a direct relationship between a given amount of greenhouse gas emissions and the number of ice-free days in areas inhabited by bears — which in turn affects the proportion of bears that reach adulthood.

With this degree of precision, the authors of this study hope they can address what is seen as a flaw in American law.

Polar bears have been classified as a threatened species since 2008, under the protection of the US Endangered Species Act.

But a legal argument, published in the same year, prevented this law from being used to evaluate new permits for fossil fuel projects in light of climate considerations and their impact on these species.

This argument, written by David Bernhardt, a lawyer in the administration of Republican President George W. Bush, claimed that science is unable to distinguish between the effect of a specific source of greenhouse gases, versus the effect of all emissions.

“We have provided the information necessary to analyze this argument,” Stephen Amstrup, one of the study’s authors, told AFP.

Cub Survival –

Polar bears need ice floes to hunt seals, move around and reproduce.

When it thaws in summer, they retreat inland or to the ice away from the coast, where they can remain for a long time without eating. These fasting periods are becoming longer as global warming intensifies.

A major study published in 2020 was the first to calculate the relationship between observed changes in sea ice due to climate change and the number of polar bears.

Building on this work, the authors of this new study established the relationship between greenhouse gas emissions and the number of fasting days, as well as the survival rate of young cubs.

They made these calculations for 15 out of 19 subpopulations of polar bears, between 1979 and 2020. We were able to draw several conclusions.

For example, the world currently releases 50 billion tons of carbon dioxide or equivalent gases into the atmosphere annually, which according to the study reduces the survival rate of cubs in the polar bear community by 3% per year.

In healthy populations, the survival rate of cubs through their first years of life is about 65%.

“There doesn’t need to be a lot of variation in decline so that there won’t be enough cubs in the next generation,” says Mr. Amstrup.

The study also provides US authorities with the tools necessary to measure the impact of new fossil fuel projects, such as new power plants, on polar bears. This technique can also be applied retrospectively to understand the past impact of a particular project.

– “Indisputable link”

For Joel Berger, a wildlife conservation researcher at Colorado State University, this new study establishes “an indisputable quantitative link between emissions (greenhouse gases, editor’s note), sea ice decline, fasting duration (…)” and composition Population of polar bears.

This work could have implications beyond polar bears – for example, they could adapt to other species, such as coral or deer in the Keys, believes co-author Cecilia Betz.

“I really hope this will lead to a lot of scientific research,” she told AFP, adding that she is always looking for new collaborations.