The agency projects that polar bears during that time will lose 42 percent of the Arctic range they need to live in during summer in the Polar Basin when they hunt and breed.
Polar bears depend on sea ice as a platform for hunting seals, their primary food. But the sea ice is decreasing due to climate change.
"It's that declining sea ice that appears to be driving the results in our models," said U.S. Geological Survey scientist Steven Amstrup, the lead author of the new studies. "As the sea ice goes, so goes the polar bear."
Scientists do not hold out much hope that the buildup of carbon dioxide and other industrial gases blamed for heating the atmosphere like a greenhouse can be turned around in time to help the polar bears anytime soon.
"Despite any mitigation of greenhouse gases, we are going to see the same amount of energy in the system the next 20, 30 or 40 years," Mark Myers, the USGS director, said.
Greenland and Norway have the most polar bears, while a quarter of them live mainly in Alaska and travel to Canada and Russia. But the USGS says their range will shrink to no longer include Alaska and other southern regions.
The findings of U.S. and Canadian scientists are based on six months of new studies, during which the health of three polar bear groups and their dependency on Arctic sea ice were examined using "new and traditional models," Myers said.
They were made public to help guide Interior Secretary Dirk Kempthorne's decision expected in January on his agency's proposal to add the polar bear to the government's endangered species list.
Last December, Kempthorne proposed designating polar bears as a "threatened" species deserving of federal protection under the Endangered Species Act, because of melting Arctic sea ice from global warming. That category is second to "endangered" on the government's list of species believed most likely to become extinct.
A separate organization, the World Conservation Union, based in Gland, Switzerland, has estimated the polar bear population in the Arctic is about 20,000 to 25,000, put at risk by melting sea ice, pollution, hunting, development and tourism.