FILE - In this Dec. 18, 2009 file photo, President Barack Obama speaks at the morning plenary session of the United Nations Climate Change Conference in Copenhagen, Denmark. Obama propo

 

              FILE - In this Dec. 18, 2009 file photo, President Barack Obama speaks at the morning plenary session of the United Nations Climate Change Conference in Copenhagen, Denmark. Obama propo
FILE - In this Dec. 18, 2009 file photo, President Barack Obama speaks at the morning plenary session of the United Nations Climate Change Conference in Copenhagen, Denmark. Obama proposed a bill that would have capped power plant carbon dioxide emissions and allowed trading of credits for the right to emit greenhouse gases, but the measure subsequently died in Congress, and his international treaty effort failed. He has since taken a different approach, treating carbon dioxide as a pollutant under the law. (AP Photo/Susan Walsh, File)