Climate Change Is Forcing Polar Bears North—Here’s Why That’s Bad News

As sea ice disappears, bears are concentrating in the High Arctic, decreasing their genetic diversity and chances of survival.

(Photo: Chris Wattie/Reuters)

Jan 9, 2015· 1 MIN READ
Katharine Gammon has written for Nature, Wired, Discover, and Popular Science. A new mom, she lives in Santa Monica.

As climate change melts Arctic sea ice, Canadian polar bears seem to be migrating permanently from the south to take up year-round residence in the country’s High Arctic islands.

The result: A decrease in genetic diversity that could hurt the species’ chances of survival in coming decades.

Using blood samples from four Canadian polar bear populations, an international research team analyzed the DNA of each group. It found that over the last one to three generations a one-way flow of genetic material has developed, toward the Canadian Archipelago and its year-round supply of sea ice.

What this means on the ground is that the more southern polar bear populations are drifting northward and then pretty much staying put, while no Archipelago bears are moving south. This increases the risk of polar bears going extinct in the wild, because an animal population that becomes isolated may begin to inbreed and weaken genetically.

“This movement of genes is not necessarily a bear packing up and heading north, but it’s a subtle inching of animals through mating and migration happening over generations,” said Lily Peacock, a wildlife biologist with the U.S. Geological Survey and coauthor of the new study, published this week in the journal PLOS ONE.

In polar bear habitats outside the Canadian Archipelago, sea ice has always been seasonal. The bears have to survive the ice-free months on land, where it’s harder for them to hunt and there’s a higher likelihood of dangerous run-ins with humans. Climate change has lengthened the number of ice-free days in these areas, intensifying those challenges.

In the Canadian Archipelago, meanwhile, the ice still lasts year-round, and the bears can hunt all the time on their favorite terrain.

Peacock noted that this population shift isn’t something wildlife researchers are seeing with their eyes. Rather, the genetic information in the study gives a sense of what may become a larger likelihood in the future.

There might be an upside, she said, in that a slightly warmer world could mean more abundant prey for the bears in the Canadian Archipelago, aiding their survival as a species. Right now, the ice there is so thick that light can’t penetrate it well. Less light means less phytoplankton, which means less food for seals—and thus fewer seals for bears to eat.

With climate change, the ice could become thinner, and perhaps even seasonal rather than year-round, allowing more of the sun’s energy to penetrate the ocean, which in turn could drive up productivity in the marine food web.

“While this improvement may happen, it could just be an intermediary betterment,” said Peacock. “With seasonal ice, the ice-free period of the year will become longer and longer, which makes the bears come on land more.”

The Canadian Archipelago has long been seen as a possible refuge for polar bears under siege from climate change. But in December, a different study found that the area may not endure the warming world better than other polar bear habitats, and may ultimately fail to sustain the species.

“If polar bears are going to continue to live anywhere in the Arctic, it’ll be where ice is going to persist,” Peacock said.