The Bush administration - out of touch with much of the world and much of the nation over climate change - has been put under even greater pressure to take action to deal with global warming as a result of the Intergovernmental Panel on Climate Change's findings.
As Washington continues to refuse to impose limits on carbon emissions - even while governments at state level are taking action in this area - Mr Bush was urged to adopt a new policy immediately.
Senator John Kerry, author of one of several congressional bills seeking to address climate change, said: "Although President Bush just noticed that the earth is heating up, the American public, every reputable scientist and other world leaders have long recognised that global warming is real and it's serious. The time to act is now."
The White House, which rejected the Kyoto treaty, sought to muddy the science about climate change and rejects binding international agreements on the way forward, issued a statement saying the administration has devoted $29bn to climate-related science, technology and international assistance - "more money than any other country".
Last week Mr Bush called for a 20 per cent reduction in petrol consumption over the next 10 years in the US, which is responsible for 25 per cent of the world's greenhouse gas emissions.
Yvo de Boer, the top UN climate official, said: "The findings leave no doubt as to the dangers mankind is facing and must be acted upon without delay.
"Any notion that we do not know enough to move decisively against climate change has been clearly dispelled."
In London, the Environment Secretary, David Miliband, warned the planet faced "catastrophic consequences" unless world leaders took steps to combat climate change.
He led pleas from politicians of all parties for a fresh effort by the international community.
Peter Ainsworth, the shadow Environment Secretary, said: "The science is clear - mankind is responsible for climate change. Now we must be responsible for preventing it. The good news is that the technology to tackle the problem already exists.
"But if we are to stop climate change, we need a cultural change too. This has to come from the Government, because it is they who set the rules of the game for everyone else."
Chris Huhne, the Liberal Democrat environment spokesman, said tackling global warming was "achievable and affordable'". He added: "Rather than tinkering around the edges, Gordon Brown must make a serious effort to use the tax system to change people's behaviour. We need greener and fairer taxes, but not higher taxes overall."Reuse content