The U.S. government has decided to list polar bears as a threatened species under its Endangered Species Act because of the effects of global warming - a decision lauded by wildlife groups, but that could deal a severe blow to the lucrative sport hunt in Canada's North. U.S. Secretary of the Interior Dirk Kempthorne, who made the announcement in Washington on Wednesday, said the decision was based on findings that polar bears' sea ice habitat, vital to their survival, has dramatically melted in recent decades. He said computer models projected declines in sea ice averaging 30 per cent by the middle of the century. Scientists predict that as a result, two-thirds of polar bears could disappear by then. “Because polar bears are vulnerable to this loss of habitat, they are, in my judgment, likely to become endangered in the foreseeable future. In this case, [in] 45 years," Kempthorne said. A threatened species is considered likely to...