The governments of more than 90 nations agreed last night that man-made global warming was already under way. The earth's climate appears to have been altered by pollution, a UN panel of government experts concluded.
The gradual, unsteady warming of the globe seen throughout this century was the best available evidence of this, the UN's inter-governmental panel on climate change (IPCC) said. It goes beyond natural variation.
The 1980s and 1990s have had most of the warmest years since world-wide temperature records began nearly 140 years ago. The warming is set to accelerate into and through the next century, with temperature rises faster than any of the past 10,000 years.
The panel's declaration, after three days of torturous negotiation in Madrid, marks a decisive shift in the global-warming debate.
Sceptics have claimed there is no sound evidence that climate has been changed by the billions of tonnes of carbon dioxide and other heat-trapping "greenhouse gases" spewed into the atmosphere each year, mostly from the burning of fossil fuels and forests.
But the great majority of governments and climate scientists now think otherwise and are now prepared to say so. "The balance of evidence suggests a discernible human influence on global climate," the IPCC's summary of its 200-page report says. The last such in-depth IPCC report was published five years ago and was far more cautious.
Two of the world's biggest oil producing states, Saudi Arabia and Kuwait, made a sustained effort to water down the new report. They fear that if governments take global warming seriously they will shift their economies into using less crude oil. The two petroleum states relied heavily on briefings in Madrid from two US-based pro-fossil fuel lobbying organisations.
But despite the opposition, the IPCC science working group concluded average temperatures have risen by 0.3 to 0.6C this century and have been "at least as warm as in any other century since AD1400".
"The recent warming has been greatest of the mid-latitude continents in winter and spring," the report says. Britain's experience in recent mild winters fits well with that.
Sea levels have crept up by as much as 25 centimetres - nearly a foot - over the past 100 years as warmer oceans expand. Atmospheric concentrations of the heat-trapping greenhouse gases, chiefly carbon dioxide, methane and nitrous oxide, continue to rise.
As for the future, the report says average temperatures could rise by a modest 1C and a hugely damaging 3.5C by 2100. Sea levels could rise by between 15cm and 95cm by then.
The meeting ended at midnight after occasionally bitter exchanges. The chairman of the panel, Sir John Houghton, a former head of Britain's Meteorological Office, said: "We are beginning to see the effect of our emissions on the climate. That's a big step - the last time round we said we could not yet see it."
Jeremy Leggett, a scientist employed by Greenpeace, said in Madrid last night: "This has got to be a turning point. We've seen a clear signal that the footprint of climate change is appearing in the sand and is going to be increasingly hard for governments not to act."
The debate is now over what steps are necessary to address the threat to economies, farming and people's health that global warming poses. Despite the new consensus that it is now under way, the fossil fuel industries and several governments will argue that the changes are so slow and small that little needs to be done.
Two other IPCC working groups have reported on the likely impacts of global warming, and what can be done to counter or adapt to the threat.
All three reports will be pulled together at a meeting in Rome next month, then presented as the UN's official advice to world governments.
There is an international treaty aimed at combating global warming, signed by some 200 leaders at the 1992 Earth Summit in Rio de Janeiro. It provides a legal framework for restraining or even cutting the growing volume of greenhouse gases.
But it has had very little impact; the only real commitment is for developed countries to try to stabilise their rising emissions of carbon dioxide at the 1990 level by 2000. Britain is one of the few that will.
By 1998, developed countries have promised to make a commitment on limiting emissions of greenhouse gases after the year 2000, but this will not cover newly industrialised nations such as China and India which are now rapidly increasing consumption of coal, oil and gas.Reuse content