World leaders gathered at the United Nations on Tuesday for a one-day global summit on climate change. The conference comes just over two months before the major climate summit in Copenhagen to replace the 1997 Kyoto Protocol. In his first UN address, President Obama said the US is “determined” to act on global warming but offered no specific proposals to jumpstart talks on a UN climate pact.

President Obama: “The threat from climate change is serious. It is urgent, and it is growing. Our generation’s response to this challenge will be judged by history, for if we fail to meet it boldly, swiftly and together, we risk consigning future generations to an irreversible catastrophe.”

Chinese President Hu Jintao, meanwhile, vowed to cut emissions by a “notable” margin but did not provide specifics. The Chinese plan would also link the size of its reductions to its rate of economic growth. The gathering also heard from the Nobel Peace Prize-winning Kenyan environmentalist Wangari Maathai, who called global warming the “challenge of all time.”

Wangari Maathai: “Unlike delegations and negotiators, Your Excellencies have the power to turn this around in Copenhagen. There is no time to lose. This is the challenge of all time. Addressing it will take collective political will. No part of the world is immune. We are all in this together, irrespective of our level of contribution to the problem. Business as usual for any one country would be a tragedy.”