Summit of world 's largest cities meeting in Copenhagen to discuss climate change . Ex - U.S. President Clinton says cities must always lead with green policies . The Seoul summit is the third conference by cities held to discuss responses to climate change . Initiative by cities began in 2008 in Copenhagen . Plans to hold climate summit at end of year in Denmark .
Summit of world 's largest cities meeting in Copenhagen to discuss climate change . Ex - U.S. President Clinton says cities must always lead with green policies . Initiative by cities began in 2008 in Copenhagen . Plans to hold climate summit at end of year in Denmark .