U.S. President Barack Obama and European Union leaders pledged on Tuesday to redouble efforts for a deal on climate change at a summit in Copenhagen, but gave no details of how to reach that ambitious goal. "We discussed climate change extensively and all of us agreed that it was imperative for us to redouble our efforts in the weeks between now and the Copenhagen meeting to ensure that we create a framework for progress," Obama told reporters. The U.N. conference to fight climate change will be held in Copenhagen from December 7 to 18, pitting emerging economic powerhouses China and...