Associated Press: Conservation groups announced Tuesday they are challenging Interior Secretary Dirk Kempthorne’s attempt to limit collateral economic damage from listing polar bears as a threatened species. The Center for Biological Diversity/, Greenpeace and the Natural Resources Defense Council will seek court intervention to address what they say in the No. 1 threat to polar bears: greenhouse gas emissions that cause global warming and melt Arctic sea ice. Kempthorne, echoing President Bush, …