redOrbit: The U.N.’s top climate official said on Tuesday that the United States and other rich nations must pledge specific targets by the end of next year for cutting greenhouse gas emissions by 2020 to win agreement on a U.N. climate pact. But many analysts predict that President-elect Barack Obama may not be ready to set formal emissions targets for 2020 within a year, and that economic recession could delay an end-2009 deadline by 190 nations for agreement on a new U.N. global warming …