Study Forecasts Poor Future for Polar Bears

By Xander Zellner for National Geographic Polar Bear Watch

An adult male polar bear pauses at the edge of the Chukchi Sea (Photograph U.S. Geological Survey).

A recent study found that greenhouse gas emissions remain the number one threat posed to polar bears. The study, released on June 30 by the U.S. Geological Survey, predicts a decline for polar bear populations across all four ecoregions of the Arctic by the end of the century.

From Canada to Russia, polar bear populations in all of the ecoregions are at risk. Using sea-ice projections from the Intergovernmental Panel on Climate Change, researchers compared future polar bear populations under two different scenarios. The first projects a stabilized climate with reduced carbon emissions, the second with emissions continuing at their current rate. In both cases the projection for polar bears isn’t good. The study builds on previous scientific work from 2010 and 2007.

Todd Atwood, a USGS biologist and lead author of the study, said he and his team compared greenhouse gas emissions to other polar bear population stressors, such as conflict with humans, exposure to contaminants such as oil, gas, and mining activity, and parasitic foods and disease. “Everything else paled in comparison,” Atwood said.

“[Greenhouse gas emissions] are responsible for the rise in ambient temperature, and without sea-ice habitats, polar bears have no access to prey,” Atwood said.

When sea ice melts during the summer, polar bears are forced to retreat onto land, where seals, their traditional prey, are unavailable and other rich food sources—such as walruses or bird eggs—are too few to maintain populations.

The study projected that all four ecoregions will see significant decreases in polar bear populations. The Archipelago ecoregion, which, at a higher latitude, retains its ice for a longer period, is likely to be the last polar bear stronghold. Atwood said it’s possible that some displaced polar bears could move to this region, but the area is only so big. “I estimate [the Archipelago] is supporting as much as it can right now,” Atwood said.

The Polar Bear Specialist Group has estimated that the Archipelago region, defined as islands in the Canadian high Arctic and Greenland, has about 5,000 polar bears, the third most populated polar bear area in the four ecoregions. Of the roughly 20,000 to 25,000 polar bears worldwide—all of which live near the northern Arctic nations—Atwood said it’s highly unlikely the region could support the rest of the bears as their habitat disappears.

The U.S. Fish and Wildlife Service announced a draft conservation plan for polar bears following the release of the study.

“The single most important step is decisive action to address Arctic warming,” the U.S. Fish and Wildlife Service (USFWS) said in a news release on July 2. The polar bear was listed as threatened under the Endangered Species Act in 2008.

The USFWS conservation plan outlines ways to reduce risks of contamination from oil and chemical spills, as well as protect polar bear habitats from human disturbances. But the study also shows that “on the ground” management efforts cannot help long-term polar bear survival in the absence of greenhouse gas mitigation.

Steven Amstrup, chief scientist for Polar Bears International and an author of the study, said he hopes the findings spark public interest to reduce greenhouse gas emissions.

“Polar bears are perhaps the best symbol of how we are altering our planet,” Amstrup said. “And if we recognize that and take actions in time to save the polar bears, we will benefit ourselves and the rest of life on Earth.”

Follow Xander Zellner on Twitter @XanderZellner.