Plummeting polar bear numbers have been directly linked to greenhouse gas emissions for the first time.
The breakthrough will enable greater legal protection for the iconic species, say scientists.
Research quantifying the relationship between greenhouse gas emissions and the survival of polar bear populations was conducted by the University of Washington and US-based conservation group Polar Bears International.
The study, published in the journal Science, combines previous research and new analysis to provide a quantitative link between greenhouse gas emissions and polar bear survival rates.
The research team explained that a warming Arctic is limiting polar bears’ access to sea ice, which the bears use as a hunting ground.
During ice-free summer months, the bears must fast.
While in a worst-case scenario, the adult bears will die, before then they will lose the ability to successfully raise cubs.
Study second author Professor Cecilia Bitz, of the University of Washington, said: “Until now, scientists hadn’t offered the quantitative evidence to relate greenhouse gas emissions to population decline.”
She analyzed data for the study that revealed a direct link between cumulative greenhouse gas emissions and polar bear population changes.
She said the link largely explains recent declining trends in some polar bear subpopulations, such as in western Hudson Bay.
Bitz says the paper also has policy implications because it allows a formal assessment of how future proposed actions would impact polar bears.
She said: “I hope the US government fulfills its legal obligation to protect polar bears by limiting greenhouse gas emissions from human activity.
“I hope investments are made into fossil fuel alternatives that exist today, and to discover new technologies that avoid greenhouse gas emissions.”
Polar bears became the first species listed under the Endangered Species Act in 2008 because of the threat of climate change.
The biological link between warming and polar bear survival was clear and scientists projected that up to two-thirds of the world’s polar bears could disappear by 2050.
The Endangered Species Act requires that any government-authorized projects, including oil and gas leases, do not further endanger any listed species.
But a document released by the US Department of the Interior in 2008, known as the Bernhardt Opinion, required specific proof of how a proposed project’s greenhouse gas emissions would affect a species’ survival before the ESA could be fully implemented for species threatened by climate change.
Study lead author Dr. Steven Amstrup, chief scientist emeritus at Polar Bears International, said: “We’ve known for decades that continued warming and sea ice loss ultimately can only result in reduced distribution and abundance of polar bears.
“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.”
He says advances in climate science mean that precise links can now be established between emissions and species survival.
The new paper links ice-free days and polar bear fasting limits to cumulative greenhouse gas emissions.
(Cecilia Bitz/University of Washington via SWNS)
It suggests that, for example, hundreds of power plants in the US will emit more than 60 gigatons of greenhouse gas emissions over their 30-year lifespans, which would cut polar bear cub survival in the southern Beaufort Sea population by around four percent.
Bitz said: “Overcoming the challenge of the Bernhardt Opinion is absolutely in the realm of climate research.
“When the memo was written in 2008, we could not say how human-generated 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 our greenhouse gas emissions.”
The research team says their study has implications beyond polar bears and sea ice.
They believe the same method of analysis can be adapted for other species and species habitats with direct connections to global warming – including coral reefs and beach-nesting species that are affected by rising sea levels.
Bitz said: “Polar bears are beautiful creatures, and I hope they survive global warming.
“However, the health and well-being of humans, especially the most vulnerable, is of the utmost importance.
“All of us have experienced heat extremes in the last few years. The harm is inescapable.”
She added: “Everything governments and industries can do to reduce greenhouse gas emissions matters, and will help avoid the worst consequences.
“I’m excited to see the innovative proposals for the Inflation Reduction Act – I hope they stimulate the healthier future that polar bears, and all of us, need.”
Produced in association with SWNS Talker
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