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Shrinking Sea Ice Could Put Polar Bears In Grave Peril By 2100


In more environmental news, if the Arctic continues to feel the effects of unchecked climate change, scientists predict serious challenges for polar bears. Those bears will eventually have only one last stronghold, Canada's Arctic Archipelago. That's the big tangle of islands way up north, in the middle of Canada. Now researchers have new predictions about when even that refuge may not have enough sea ice to support the bears. NPR's Nell Greenfieldboyce explains.

NELL GREENFIELDBOYCE, BYLINE: Sea ice is just a layer of frozen, floating sea water. And it's the polar bears' main hunting ground because underneath the ice, there's seals. Polar bears sniff around until they find the breathing hole of a seal that's swimming down below. And when the seal bobs to the surface, they grab it. Stephen Hamilton is part of a team at the University of Alberta that studies polar bears. He says, they can eat other things, but almost always a polar bear meal is a ringed seal or a bearded seal.

STEPHEN HAMILTON: In order to feed on those species, they basically need the ice.

GREENFIELDBOYCE: Hamilton says, way up north, there is currently sea ice year-round, but farther south, in summer, there's ice-free periods. And as the world warms, scientists expect to see less ice and longer and longer ice-free periods everywhere, even around the far northern islands in Canada where a quarter of the world's polar bears live.

HAMILTON: The Archipelago was kind of hoped to be the space that would hold onto the ice a little longer than the rest of the polar bear area.

GREENFIELDBOYCE: Hamilton and his colleagues recently looked at some new predictions about how sea ice will change in that region in the coming decades, assuming nothing is done to slow climate change. And they combined those predictions with some recent findings from studies of bears in Hudson Bay. There, the sea ice melts in the summer. Scientists have tracked what happens to those bears as they went for long periods without access to their main food.

HAMILTON: For example, we start to see some starvation in adult males when we have 120 days of ice-free season.

GREENFIELDBOYCE: Hamilton says, that study showed if the ice-free season stretches out to 180 days, over 20 percent of the bears could starve. His group calculated how long it would take for bears living in the Canadian Arctic Archipelago to reach these kinds of critical thresholds.

HAMILTON: We're probably looking at the latter half of the century and maybe almost all the way towards 2100.

GREENFIELDBOYCE: The researchers have just published their analysis in a science journal called Plos One. Steve Amstrup is with the conservation group Polar Bears International. He says, the strength of this study is that it makes predictions for specific locations across northern Canada.

STEVE AMSTRUP: It's a first attempt at looking at the when of polar bears in different areas are likely to be affected.

GREENFIELDBOYCE: He says, while it may take time for the most northern areas to feel the impact, bears in more southern regions are being hit now.

HAMILTON: When I first went to Alaska in the early 1980s, I could stand on the beach in the summer time and look offshore and see the sea ice. Now the sea ice is beyond the curvature of the earth. It's hundreds of miles offshore over deep, unproductive water.

GREENFIELDBOYCE: A study by his team, also published this week, looked at bears there in the southern Beaufort Sea from 2001 to 2010. He says that population declined from 1,500 bears to just 900 bears. Nell Greenfieldboyce, NPR News. Transcript provided by NPR, Copyright NPR.

Nell Greenfieldboyce is a NPR science correspondent.