Reuters: The United States unveiled its proposal to cut greenhouse gases by 2020 on Wednesday and said President Barack Obama will attend U.N. climate talks in Copenhagen next month — before other world leaders show up. Obama will go to the December 7-18 talks in Denmark on December 9, the eve of a ceremony in nearby Oslo, Norway, where he will collect the Nobel Peace Prize, the White House said. He is not scheduled to return, however, for the final days when most of the hard …