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Study confirms direct link between polar bear survival and harmful emissions

New research published in the journal Science has quantified the link between greenhouse gas emissions and the survival of polar bear populations, paving the way for greater protections under the Endangered Species Act. 

The study, which was a collaboration between the University of Washington  and Polar Bears International, combines past and new research to provide a quantitative link between greenhouse gas emissions and polar bear survival rates. 

Studying polar bear survival

As the Arctic warms, polar bears have increasingly limited access to sea ice, their hunting platform. They are forced to fast during ice-free summer months. This threatens the survival of adult bears, as well as their ability to successfully raise cubs.

“Until now, scientists hadn’t offered the quantitative evidence to relate greenhouse gas emissions to population decline,” said second author Cecilia Bitz, a UW professor of atmospheric sciences. 

Professor Bitz’s data analysis for the new report shows a direct link between cumulative greenhouse gas emissions and polar bear demographic changes. The results largely explain recent declining trends in some polar bear subpopulations, such as in western Hudson Bay. 

The confirmation of this link has significant policy implications, as it enables a formal assessment of how future proposed actions would impact polar bears. 

“I hope the U.S. government fulfills its legal obligation to protect polar bears by limiting greenhouse gas emissions from human activity,” said Professor Bitz. “I hope investments are made into fossil fuel alternatives that exist today, and to discover new technologies that avoid greenhouse gas emissions.”

Endangered species

In 2008, polar bears became the first species listed under the Endangered Species Act 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 mid-century.

Still yet, the ESA required specific proof of how a proposed project’s greenhouse gas emissions would affect a species’ survival before it could be fully implemented for species threatened by climate change.

Cub survival rates 

“We’ve known for decades that continued warming and sea ice loss ultimately can only result in reduced distribution and abundance of polar bears,” said lead author Steven Amstrup, chief scientist emeritus at Polar Bears International and adjunct professor at the University of Wyoming. 

“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.”

Advances in climate science

This new paper, published in the 50th anniversary year of the Endangered Species Act and the 15-year anniversary of the listing of polar bears, brings new science to fill this knowledge gap. 

Advances in climate science now enable precise links to be established between emissions and species survival. 

Professor Bitz co-authored a 2020 Nature Climate Change study that modeled polar bear survival against sea ice decline, connecting polar bear fasting to ice-free days and calculating the annual fasting limits that lead to mortality. 

This study considered not just adult polar bear survival, but also its recruitment success, meaning its ability to have cubs and raise them to the age of independence. 

Cumulative greenhouse gas emissions

The new paper links ice-free days and polar bear fasting limits to cumulative greenhouse gas emissions. 

The experts found that the hundreds of power plants in the U.S. will emit more than 60 gigatons of greenhouse gas emissions over their 30-year lifespans, reducing polar bear cub survival in the southern Beaufort Sea population by about four percent.

“Overcoming the challenge of the Bernhardt Opinion is absolutely in the realm of climate research,” said Professor Bitz. “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.”

Study implications 

The study’s implications extend beyond polar bears and sea ice, the authors say. The same method of analysis can be adapted for other species and species habitat with direct connections to global warming, such as coral reefs, the endangered Key deer that reside in the Florida keys, or beach-nesting species affected by rising sea levels.

“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,” said Professor Bitz. 

“All of us have experienced heat extremes in the last few years. The harm is inescapable. 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.”

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More about polar bears

Polar bears, often referred to as the kings of the Arctic, are iconic animals that captivate the imagination of many. Majestic and powerful, these bears are uniquely adapted to life in the extreme cold conditions of the Arctic region.

Physical features

A polar bear’s striking white fur offers it more than just camouflage amidst the snow and ice. This fur also provides a thick layer of insulation against the cold, while its black skin underneath absorbs and retains the sun’s warmth.

Additionally, a thick layer of blubber, sometimes measuring up to 4 inches, gives the bear buoyancy in water and acts as another layer of insulation.

Diet and hunting techniques

Polar bears are carnivorous, with seals, especially ringed and bearded seals, being their primary source of food. Their keen sense of smell, which can detect a seal from nearly a mile away, aids them in their hunt.

Using their massive front limbs, they can swim for miles or break through thick layers of ice to catch their prey. The bear will often wait patiently by a seal’s breathing hole, ready to snatch it as it emerges.

Habitat and distribution

The ice-covered waters of the Arctic Circle serve as the primary habitat for polar bears. These bears do not hibernate like other bear species.

Instead, they are continuously active, often wandering large distances in search of food. Polar bears are found across five nations: the U.S. (in Alaska), Canada, Russia, Greenland, and Norway.

Threats and conservation

Unfortunately, as mentioned previously in this article, polar bears face significant threats. This is primarily due to climate change.

The melting of Arctic ice reduces the bears’ hunting grounds and makes it challenging for them to find food. As a result, many bears are now found malnourished, and some even resort to cannibalism.

Conservation efforts are underway to protect polar bears and their habitats. Measures include setting up protected areas, reducing human-bear conflicts, and taking steps to address climate change. Researchers and conservationists continue to monitor polar bear populations and health to devise strategies to help them thrive in a changing world.

In summary, polar bears are a testament to nature’s ability to adapt and survive in harsh conditions. Their plight serves as a stark reminder of the impacts of climate change, urging us to take collective action for their survival.


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