Politics still stand in the way of efforts to limit U.S. greenhouse gas emissions. Two efforts, the American Clean Energy and Security Act (ACES) of 2009 and the American Power Act of 2010, got tabled or failed to make it to the Senate floor for a vote. ACES was, however, passed by a narrow margin in the House of Representatives, the first time the legislative branch has called for sweeping climate legislation. (Media credit/Rachel Johnson via Flickr)