UN Secretary General Ban Ki-moon has warned climate change is putting the world on the edge of catastrophe.
Mr Ban was speaking at the publication of the latest report from the UN's climate change advisory panel.
The Intergovernmental Panel on Climate Change warned that global warming could occur abruptly and the impact could be irreversible.
The report said some of the worst effects could be avoided if action is taken immediately.
The report will set the stage for next month's meeting of environment ministers in Indonesia to agree a timeframe for negotiating a successor to the Kyoto Protocol.
The panel's chairman, Rajendra Pachauri, said even if levels of emissions in the atmosphere stayed where they are now, research showed sea levels would rise by between 0.4 and 1.4 metres, because water expands as it warms.
Inaction warning
This is the fourth and final report from the IPCC this year. The Nobel prize winning organisation will not report again until 2013.
The IPCC document predicts that inaction will lead to abrupt and irreversible changes to the world's eco-system, such as the widespread extinction of species.
Leading scientists have warned politicians that the planet is getting warmer and humans are to blame.
In a policy guide for governments, the IPCC said global warming is unequivocal, and it is virtually certain that human activity such as burning coal and oil is responsible.
It also says irreversible and disastrous change will occur unless action is taken now to reduce emissions.
On a positive note the IPCC also outlines that impacts can be reduced and at reasonable cost.
The World Wildlife Fund said that following the IPCC report politicians cannot now say they did not know what was going on.
