Environmental pressure groups accused governments, however, of failing to cut greenhouse gas emissions which the UN Intergovernment Panel on Climate Change (IPCC) said had almost certainly caused rising temperatures and would be unstoppable for centuries to come.

Chirac, opening a Paris conference on world environmental governance said: "Soon will come a day when climate change escapes all control: we are on the verge of the irreversible."

"Faced with this emergency, the time is not for half-measures. The time is for a revolution: a revolution of our awareness, a revolution of the economy. A revolution of political action."

The Paris conference aims to build support for the creation of a United Nations environment agency, with more far-reaching powers and greater means than the existing United Nations Environment Programme.

British Foreign Secretary Margaret Beckett said in a statement: "Failure to grow our economies will threaten peace and prosperity, but if we grow our economies at the expense of the climate the same peace and prosperity will be threatened."

Britain's Environment Secretary David Miliband said the UN report "is another nail in the coffin of the climate change deniers and represents the most authoritative picture to date, showing that the debate over the science of climate change is well and truly over."

Yvo de Boer, executive secretary of the UN framework convention on climate change, said in a statement: "The world urgently needs new international agreement on stronger emission caps for industrialized countries, incentives for developing countries to limit their emissions and support for robust adaptation measures."

Environment groups said it was up to governments to act to halt global warming that causes rising seas and unpredictably fierce storms.

Friends of the Earth said the world now faces a "crisis," and the WWF International conservation group said governments must now "slash emissions." Greenpeace warned the "window for action is narrowing fast".

"The IPCC report embodies an extraordinary scientific consensus that climate change is already upon us and that human activities are the cause," said WWF International director general James Leape.

"It is a clarion call to governments to act urgently to slash emissions," he added in a statement.

Jan Kowalzig, climate and energy campaigner for Friends of the Earth, said "The IPCC report scientifically confirms the extent of this man-made crisis already hitting people around the world and makes bleak predictions for the future."

Greenpeace climate and energy campaigner, Stephanie Tunmore, said "There's a clear message to governments here, and the window for action is narrowing fast. If the last IPCC report was a wake up call, this one is a screaming siren."

WWF and Friends of the Earth urged the European Union, at a summit next month, to take a leading role in international efforts to control greenhouse gas emissions.

Kowalzig said EU leaders must order a 30 percent emissions reduction target "which would be just enough to avert the worst of climate change."

WWF said governments must ensure the next UN Climate Conference is a success. Hans Verolme, head of the WWF global climate change programme, called for a "tight time frame for negotiating new cuts in emissions within a next Kyoto Agreement that will also promote clean investments."

The annual UN climate change conference is to be held in the Indonesian resort of Bali in December.

The Kyoto protocol is the only international treaty to set targets for limiting the fossil fuel pollution that causes the greenhouse effect. It has been rejected by the United States.

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