But UN Secretary-General Ban Ki-moon called the meeting more to build momentum than to reach concrete achievements. It was the first such event since the Copenhagen summit on climate change ended in disarray in 2009 and aims to set the tone for a conference next year in Paris designed to seal a new global agreement.
French President Francois Hollande said the Paris conference should deliver a "global and ambitious" deal and warned that climate change posed a "threat to world peace and security." US President Barack Obama, addressing the summit hours after ordering strikes on Syria, said that the "urgent and growing threat of climate change" would ultimately "define the contours of this century more dramatically than any other" issue.
"We know what we have to do to avoid irreparable harm. We have to cut carbon pollution in our own countries to prevent the worst effects of climate change," Obama said. Obama called for an "ambitious" but also "flexible" agreement - a nod to political difficulties he would face if he needed the US Congress to ratify a treaty. Developing nations have balked at signing on to a binding accord without firm US commitments, noting that wealthy countries bear historic responsibility for climate change.
Obama said he met in New York with Chinese Vice Zhang Gaoli - President Xi Jinping was notably absent - and told him that the world's two largest economies "have a special responsibility to lead" on climate change. Zhang said that China, which has surpassed the United States as the world's top carbon polluter, wanted its emissions to peak as soon as possible. He was not more specific but senior official Xie Zhenhua told reporters that China was making good on reductions in its carbon intensity and would announce early next year a prediction of when its emissions would peak. Activist group ActionAid criticised the summit for offering just "vague promises" on climate change despite the unprecedented international demonstrations on Sunday that urged immediate action.