Agence France-Presse: US President Barack Obama on Tuesday said it was “imperative to redouble our efforts” to combat global warming ahead of key climate change talks in Copenhagen next month. He was speaking as European leaders urged the US Congress to take action on climate change ahead of next month’s high-stakes summit. Obama said they discussed climate change “extensively and all of us agreed that it is imperative for us to redouble our efforts in the weeks between now and the Copenhagen …