Ban Ki-moon, Secretary-General of the United Nations, speaks as French President Hollande looks on at the Paris Agreement signing ceremony on climate change held at the United Nations Headquarters in New York

Ban Ki-moon (2nd from R), Secretary-General of the United Nations, delivers his opening remarks at the Paris Agreement signing ceremony on climate change as French President Francois Hollande (2nd from L) looks on at the United Nations Headquarters in Manhattan, New York, U.S., April 22, 2016. REUTERS/Mike Segar