Because of global warming, the polar bear population is likely to shrink to one-third of its current size within 50 years, according to the United States Geological Survey (USGS). The report was coordinated by Steven Amstrup of the USGS Alaska Science Center.
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You've been studying polar bears for 27 years. Were they in trouble when you started?
No. At that time the big issue was making sure they were not overharvested. There had been a lot of trophy hunting and commercial harvest for hides, and Native people had always hunted them. In the 1970s, an agreement by the five polar nations [the United States, the Soviet Union, Canada, Norway and Denmark] got harvest under control.
Why is global warming so bad for polar bears?
They feed almost entirely from sea ice. They catch seals as they come up to breathe or climb onto the ice. This year set a new record for melting sea ice.
Have you seen much change in your study area?
Most of my research is in the Beaufort Sea of northern Alaska. We have already seen major changes in habitat. The sea ice still freezes in winter, but it's retreating dramatically in the summer. Historically, polar bears followed the ice. Now they're forced to stay on land or follow the ice farther north, where there's less to eat.
Will they also have trouble breeding?
My work suggests that polar bears typically build dens [where they raise their young] wherever they finish foraging at the end of the summer. It's not clear how far they have to be from historic denning areas before polar bears won't bother to return or won't be able to return.
This summer, the northwest passage opened up for the first time in history. Is that bad for polar bears?