New Research Shows Direct Link Between Greenhouse Gas Emissions and Polar Bear Decline

In 2008, polar bears had the dubious distinction of being the first animal placed on the United States’ endangered species list due to climate threats, specifically the loss of Arctic sea ice. 

But that same year, President George W. Bush’s Interior Department adopted a new policy that prevented federal agencies from considering the effects of greenhouse gas emissions on polar bears, despite those emissions being the main driver of the climate threat to the keystone Arctic predators. Every new ton of emissions leads to more melting of the sea ice that the bears live on. 

The policy-setting 2008 memo was written by Dave Bernhardt, a former fossil fuel industry lobbyist then working as solicitor for the Interior Department who would go on to be President Donald Trump’s secretary of the interior. It required that the projected emissions impacts to polar bears from new proposals, like pipelines or drilling permits, be separated from the effects of historical cumulative emissions.

That set what seemed an impossibly high scientific bar at the time because researchers hadn’t yet fully identified the impacts of greenhouse gas emissions from specific projects on threatened species. But science has cleared that hurdle, said Steven Amstrup, an adjunct biology professor at the University of Wyoming and co-author of a new peer-reviewed paper in Science that could help “close the loophole” in the Endangered Species Act by showing how emissions from new projects on federal lands result in more days during which polar bears can’t feed because of declining sea ice.

The paper establishes a direct link between anthropogenic greenhouse gas emissions and cub survival rates using a methodology that can “parse the impact of emissions by source,” said Amstrup, also the chief science officer for Polar Bears International, a nonprofit conservation organization.

For example, the new paper notes that the hundreds of power plants in the U.S. combined will emit more than 60 gigatons of carbon dioxide over their 30-year lifespans. By calculating the amount of warming that carbon will drive, and the amount of Arctic sea ice that heat will melt, they estimate that those emissions will reduce polar bear cub recruitment in the Southern Beaufort Sea population by about 4 percent. By using that formula, they can measure how greenhouse gas emissions from a new project would affect polar bear populations, a calculation that wasn’t as clear when polar bears were listed as vulnerable. 

And the same type of analysis could be applied to measure the impacts of greenhouse gas emissions on habitat and demographic changes for other species listed as endangered, Amstrup said.

Emerging Science Supports Climate Lawsuits

Michael Burger, executive director of the Sabin Center for Climate Change Law at Columbia University, said a current legal challenge to the Willow oil and gas drilling project in northern Alaska uses a similar argument. 

“Our view is this,” Burger said. “Science supports drawing a causal connection from emissions from specific sources to climate change impacts in specific places. Studies like this one without question reinforce the argument.”

The specific impacts of greenhouse gas emissions are “particularly evident” when it comes to loss of sea ice and the impact on polar bears, the Sabin Center noted in an amicus brief submitted in support of plaintiffs challenging the Willow project, he said.

In the brief, the Sabin Center alleges that the Bureau of Land Management ignored the effect of greenhouse emissions on endangered and threatened species due to the “misconception” that science could not establish “causal links” between emissions and impacts to at-risk species. But since 2008, when the Interior Department’s memo tried to ban consideration of greenhouse gas impacts on listed species, research has made the causal connections more clear, he added. 

“What’s more, climate models and detection and attribution methods can be used to quantify the relative contributions of specific GHG sources to climate change impacts,” Burger wrote in the brief. In some cases, he said, it’s even possible to isolate the per-ton effects of greenhouse gas emissions, as was the case with a 2016 study showing that each additional metric ton of carbon dioxide results in the sustained loss of about 3 square meters of September sea ice in the Arctic.

A 2021 report from the Sabin Center summarizes the scientific findings about the impacts of climate change on endangered species, and the new study “provides useful new methodologies and evidence,” to describe those effects, said Michael Gerrard, an environmental law expert and co-founder of the Sabin Center.

Scientists and legal scholars have been telling federal agencies for quite some time that the Bernhardt Memo is incorrect, said Kassie Siegel, director of the Climate Law Institute with the Center for Biological Diversity. There are pending lawsuits that have raised that point, but no rulings yet, and the new paper adds extra scientific support to such cases.

“It is a very big deal,” said Siegel, who wrote the petition for listing polar bears as endangered species in 2004. “It’s the first time scientists have actually done the analysis and published their findings in one of the world’s leading scientific journals.”

Amstrup did the original research for the U.S. government that supported the listing of polar bears, she said. The science was so clear that the George W. Bush administration had no choice but to list the species.

But the lack of any meaningful action to protect polar bears since then has been frustrating to Siegel.

“I’m feeling a lot of grief, and I’m feeling a lot of anger, like a lot of people,” she said. “But what keeps me going is that there is still time to make a difference. There’s nothing more important than the actions taken right now to reduce greenhouse pollution.”

She said the failure of the U.S. Fish and Wildlife Service, which implements the Endangered Species Act, to properly analyze the impacts of greenhouse gas emissions on polar bears and other listed species is “a form of climate denial. It’s going against the science, and it is breaking the law.” 

“Hopefully the publication of this paper will finally convince the Biden administration to follow the science and the law,” she added.

In 2021, scientists and law professors petitioned the Biden Administration to rescind any rules that prevent agencies from considering the impacts of greenhouse gases. Failing to consider them “leaves the government blindfolded in its effort to protect threatened species,” said Stuart Pimm, a conservation scientist at Duke University who signed the petition. 

Shaye Wolfe, climate director for the Center For Biological Diversity,said the polar bear is an example of how rules like Bernhardt’s memo have weakened climate action. Without such policies, which the Trump Administration tried to further enshrine in 2019 when Bernhardt was secretary of the interior, “agencies would have another mechanism to consider and reduce carbon emissions,” Wolf said.

“Greenhouse gases are no different from mercury, pesticides or anything else that accumulates in the land, air or water and harms species,” she added. “It’s simply ridiculous not to take them into account.”

Global Warming Increasing Mass Extinction Risk

Right now, there are 1,497 animals on the U.S. endangered species list and the best available science shows that nearly every one of them faces climate-related threats, as do 1 million other species on the planet. 

The number, distribution and density of species—biodiversity—is declining rapidly in an unfolding mass extinction that could equal dramatic die-offs recorded in fossil records and attributed to planetary system-changing events like ice ages, meteor crashes or intense, massive and persistent volcanic eruptions. 

The current wave of species declines and extinctions could have profound impacts on human societies. Food security will be threatened if pollinators, seed-spreading birds or important food fish disappear. About 4 billion people rely primarily on natural medicines for their health care, while about 70 percent of drugs used to treat cancer are natural or are synthetic products inspired by nature. 

And if global warming changes the reproductive cycles of fundamental organisms like plankton, bacteria and fungi, it would have a huge effect on how much carbon dioxide oceans, fields and forests remove from the atmosphere, potentially driving even faster warming of the climate. 

Some groups of animals have been particularly hard hit, with 40 percent of amphibians and about a third of corals and marine mammals facing possible extinction, according to a 2019 United Nations global biodiversity report, which acknowledged that “Nature is essential for human existence and good quality of life.” 

“Most of nature’s contributions to people are not fully replaceable, and some are irreplaceable,” the report added.

Seen as a global call to action, the report concluded that nature is deteriorating worldwide. “The biosphere, upon which humanity as a whole depends, is being altered to an unparalleled degree across all spatial scales,” the report noted. “Biodiversity—the diversity within species, between species and of ecosystems—is declining faster than at any time in human history.”

There are numerous scientific red flags. A 2022 study showed that the current rate of ocean warming could bring the greatest extinction of sea life in 250 million years. And it’s also clear that the loss of biodiversity and the climate crisis must be addressed hand-in-hand, as a 2021 report from the United Nations noted. Global warming is an overarching threat to nearly all species, and if biodiversity collapses, some of the planet’s best natural mechanisms to remove CO2 from the atmosphere and slow atmospheric heating will fail, the report explained.

Every Ton of CO2 Brings New Misery, and Not Just to Polar Bears

Research shows that Human activities are responsible for declining polar bear habitat and most of the damage to the rest of the life-sustaining web of ecosystems and species, and those activities often intensify each other’s effects. Land impacts like urban development and industrialized agriculture strip away carbon-sequestering vegetation and destroy habitat. Greenhouse gas emissions are making parts of the ocean too hot for many fish and melting the snow that sustains wolverines high in the Rocky Mountains of the western United States.

Research like the new study could provide scientific support to get more protection for the few remaining wolverines that depend on a deep mountain snowpack for denning, said Matthew Bishop, the Rocky Mountains office director with the Western Environmental Law Center. 

Climate models and observations show most of those snowfields retreating rapidly, making it crucial to protect any remaining pockets as climate refugia. But despite the models, the federal government claims it doesn’t know enough about how wolverines will respond to the shrinking snow to act on the science, Bishop said. 

“We know they are snow dependent species and that snow is going to be gone,” he said. “That’s enough and the court agrees, but the agencies keep coming back and saying they need to know more.” At some point soon, it’s going to be too late for wolverines and many other climate-sensitive species, he added. 

“When in doubt, any kind of uncertainty should err on the side of protection for the species, and doing what we can to limit all the non-climate stressors,” he said. “Let’s give them a chance to make it. Ultimately, it may not matter. But let’s do everything we can in our power to make sure they stay on the landscape.”

For polar bears, like for wolverines, that means protecting parts of their habitat that might persist for the next 50 or 100 years, even if the outcome beyond that is uncertain. But most of all, as last week’s paper in Science emphasized, it means cutting greenhouse gas emissions immediately and quickly. 

Pairing a biologist and a climatologist for the new paper on how greenhouse gas emissions affect polar bears seemed a logical choice, said co-author Ceclilia Bitz, a scientist at the University of Washington, who studies the connection between climate, sea ice and wildlife habitat.

Focusing on the direct link between greenhouse gas emissions and polar bear habitat makes the paper policy relevant and helps paint a clear picture of the impacts of sea ice decline, she said.

“We’re saying that every additional 23 gigatons of CO2 that we emit as a world causes an additional day that the polar bears have to fast,” she said. “Currently we’re emitting about 50 gigatons per year as a planet.”

That increases the time polar bears go without eating by more than a day each year in each of their populations, she said.

“That’s huge. Imagine if you’re already hungry, going an extra day without eating,” she said. “It’s relentless. As humans, we’re emitting so much CO2 that it’s having these really perceptible and serious consequences.”

Amstrup said the new study gives people one more reference point for understanding the impact of greenhouse gas emissions.

“Polar bears depend on thresholds,” he said. “If they fast for over a certain amount of days, they simply can’t survive.”

The findings again show how closely linked the climate crisis and the biodiversity crisis are, Siegel added. “They cannot be separated,” she said. “The survival of all life on Earth, including ours, is at stake.”