After much delay, the U. S. Department of the Interior listed the polar bear as a threatened species under the Endangered Species Act on May 14 2008. The decision was based in part on a series of reports produced by the U.S. Geological Survey and collaborators from government, academia and conservation organizations. The overall conclusion of the USGS research is that projected changes in sea ice conditions, if realized, will result in the loss of about two thirds of the world's polar bear population by the mid-21st century. This talk gives an overview of the USGS reports, and shows how data from climate models, satellites, radio telemetry, and field studies were combined to assess the future status of polar bears. In addition, the extent to which polar bear habitat can be conserved through reductions in greenhouse-gas emissions is examined in simulations produced from climate change mitigation scenarios.