Climate Change Could Wipe Out Polar Bears by 2100

Polar bears will likely have almost disappeared completely by the year 2100 if greenhouse gas emissions continue along current trends, a study has predicted.

Today, these animals are found in five nations across the Arctic—the U.S., Canada, Russia, Greenland and Norway—split up into 19 subpopulations. However, global warming-driven declines in the sea-ice which they call home is forcing the animals onto land where they are deprived of food.

Polar bears can only catch their prey from the surface of sea ice. There are no foods on land that can substitute the calories they get from the seals they catch on the ice. But warmer temperatures mean the bears have less time to hunt and gain weight on productive sea ice, instead spending more time on land where they are forced to fast and live off stored fat.

"The length of time they can fast depends on how fat they can get in those ever-shorter feeding periods. So, it is all about energy balance—how fat can a bear get during good times and how long are the bad times during which it must live off of its stored fat," Steven Amstrup, one of the authors of the study from conservation non-profit Polar Bears International, told Newsweek.

For the study, published in the journal Nature Climate Change, the researchers tried to predict when polar bear populations across the Arctic will be threatened due to sea ice loss from global warming—an approach which researchers haven't taken before.

"In 2010, my colleagues and I projected we could lose two-thirds of the world's polar bears by around mid-century," Amstrup said. "To many, apparently, this projection may have seemed 'far off' and not specific enough to inspire greenhouse gas mitigation policies. The yet unanswered question has always been, 'When will bears disappear from this area or that area or my area?'"

"In this paper, we answer that question for the first time. It is my hope that presenting specific and localized timelines when polar bears are likely to cross persistence thresholds, will more effectively get the attention of the public and policy makers, and inspire action to mitigate greenhouse gas rise," he said.

In their research, the scientists first determined how many days polar bears can fast before reproduction and survival are negatively affected. Secondly, they attempted to work out how many ice-free days the future holds for polar bears in different geographic areas.

Combining these two factors revealed when polar bear reproduction and survival will begin to fail, and therefore when populations may begin to disappear in different areas.

The team's projections showed that without aggressive efforts to halt global warming polar bears may remain only in a few areas of far northern Canada by 2100 where the sea ice is expected to persist for longer than in any other region.

"We know that within a couple of decades global temperatures will exceed anything polar bears have faced in their evolutionary history. Therefore, by the end of the century we could live in a world without polar bears," Amstrup said. "The main factor leading to polar bear declines is global warming induced sea ice decline. Without sea ice polar bears cannot feed, and without adequate feeding opportunities, populations cannot persist."

For some populations, trouble will come much sooner than the end of the century. Without effective greenhouse gas mitigation, polar bears in Hudson Bay—often called the polar bear capital of the world—or other more southerly parts of the animal's range may not be able to effectively reproduce after about 2040, according to the study. And reproduction of polar bears in Alaska is likely to fail by 2060, and very likely to fail after 2080.

polar bear, Arctic
A polar bear walking on Arctic ice. Galen Rowell/Corbis via Getty Images

"In the Beaufort Sea of Alaska, reproduction may already be feeling the effects of declining availability of sea ice," Amstrup said.

The researchers say that it is not too late to save polar bears; if we reduce our emissions of greenhouse gas, many populations could survive past 2100. However, urgent action is required.

"It will take 25 or 30 years for sea ice to stabilize after we halt the rise in atmospheric greenhouse gases," Amstrup said. "If we want to save polar bears, for example in Hudson Bay, we need to aggressively mitigate greenhouse gas rise now. The same goes for polar bears across their range."

"More importantly, the polar bear is sending us a critical early warning about our own future," he said. "The sea ice on which polar bears depend is critical to maintaining the earth's climate in a state similar to the climate to which we all have become accustomed and in which humans have flourished. If societies act to mitigate greenhouse gas rise quickly enough to save polar bears, we will benefit the rest of life on earth including ourselves."

Rudy Boonstra, a researcher from the Department of Biological Sciences at the University of Toronto Scarborough, Canada, who was not involved in the study, told Newsweek the "implications of this study are dire."

"Polar bears are one of the canaries in the coal mine of what will and is happening to many species. [The researcher's] methods are as rigorous as possible, and the exact time lines for declines are believable, in spite of the uncertainty that they are forthright in laying out. I think their conclusions are robust."