UNITED NATIONS, September 22 (RIA Novosti) - The highest-level conference on climate change opened on Tuesday at the United Nations to negotiate a new deal on how to combat global warming.

The discussions will give an indication of what might be agreed at a December meeting in Copenhagen to negotiate a replacement for the Kyoto Protocol on climate change, some elements of which expire in 2012.

The overwhelming consensus of climate change experts, environmental groups and organizations is that the climate change is caused by greenhouse gas emissions due to human activity, which is causing significant damage to the Earth, although a minority argues that the possible impact has not yet been proven.

Speaking at the UN summit, U.S. President Barack Obama said: "That so many of us are here today is a recognition that 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."

"The security and stability of each nation and all peoples - our prosperity, our health, our safety - are in jeopardy. And the time we have to reverse this tide is running out. And yet, we can reverse it," he said.