Reuters: The United States and other rich nations must pledge by the end of next year specific targets for cutting greenhouse gas emissions by 2020 to win agreement on a U.N. climate pact, the U.N.’s top climate official said on Tuesday. Some analysts say 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 pact. “We …