What did the Secretary-General talk to a group of students at U. N. headquarters?

(25)Mr. Ban praised America’s role in developing innovative technology to reduce greenhouse gas emissions. Speaking Thursday to a group of students at U.N. headquarters, the Secretary-General noted that,(26)while Washington has not signed the "Kyoto Protocol" on climate change, discussions in the administration and Congress have raised public awareness about global warming.
    Answering a student’s question, Mr. Ban expressed hope that the United States, the world’s largest greenhouse gas emitter, would also take the political leads in searching for a successor to the Kyoto treaty, which expires in 2012.