Mankind is to blame for global warming, the world's top climate scientists said today, sending governments a "crystal clear" warning they must take urgent action to avert severe and irreversible damage.
The United Nations panel, which groups 2,500 scientists from more than 130 nations, predicted more droughts, heatwaves and a slow gain in sea levels that could last for more than 1,000 years even if greenhouse gas emissions were capped.
The panel's report predicts a "best estimate" that temperatures would rise by between 1.8 and 4.0 Celsius in the 21st century.
"Faced with this emergency, now is not the time for half measures. It is the time for a revolution, in the true sense of the term," French President Jacques Chirac said. "We are in truth on the historical doorstep of the irreversible."
The scientists said it was "very likely" -- or more than 90 per cent probable -- that human activities led by burning fossil fuels explained most of the warming in the past 50 years.
That is a toughening from the Intergovernmental Panel on Climate Change's (IPCC) last report in 2001, which judged a link as "likely", or 66 per cent probable.
Possible signs include drought in Australia, record high winter temperatures in Europe and dwindling fish catches in lake Chad, which is shrinking after years of poor rainfall.
Many governments, UN agencies and environmental groups urged a widening of the UN's Kyoto Protocol, which binds 35 industrial nations to cut emissions by 2012 but excludes top emitters led by the United States, China and India.
"The signal we've received from the scientists today is crystal clear and it's important that the political response is also crystal clear," said Yvo de Boer, head of the UN Climate Secretariat.
He wants an emergency environment summit of world leaders this year to push for wider action. Kyoto has been weakened since the United States pulled out in 2001 and emissions by many backers of Kyoto are far above target.
A 21-page summary of IPCC findings for policy makers outlines wrenching change such as a possible melting of Arctic sea ice in summers by 2100 and says it is "more likely than not" that greenhouse gases have made tropical cyclones more intense.
The report projects a rise in sea levels of between 18 and 59 centimetres in the 21st century -- and said bigger gains cannot be ruled out if ice sheets in Antarctica and Greenland thaw.
Rising seas threaten low-lying islands, coasts of countries such as Bangladesh and cities from Shanghai to Buenos Aires.
Temperatures rose 0.7 degrees in the 20th century and the 10 hottest years since records began in the 1850s have been since 1994. Greenhouse gases are released mainly by burning fossil fuels in power plants, factories and cars.
The head of the US delegation defended Bush's policies that brake the rise of emissions rather than cap them. Democrats who control both houses of Congress want tougher action.
Mr Bush says Kyoto-style caps would harm the economy and that Kyoto should include developing nations. He focuses instead on big investments in hydrogen and biofuels.
The president of Kiribati, a group of 33 Pacific coral atolls threatened by rising seas, said time was running out.
"The question is, what can we do now? There's very little we can do about arresting the process," President Anote Tong said.
Some leading scientists had criticised a draft for cutting the range for the rise in sea levels from a 2001 forecast of between 9 and 88 cm.
Rajendra Pachauri, the head of the IPCC, said the impact of climate change was already dangerous for some.
"Small island states will say we've already gone past the state of danger. Where you have the poorest people in the world (dependent on) rain-fed agriculture, for them also it's dangerous," he said.