After this latest report there will no longer be any serious debate about whether a large proportion of climate change is man-made. That means that the solutions are within the grasp of mankind. The question now is whether politicians are capable of tackling a problem that will bedevil the world far, far beyond their own term in office.

The political climate is already changing, partly because of the much maligned Kyoto Protocol. This agreement, signed by Europeans in 1997, was a largely symbolic effort to reduce greenhouse gas emissions.

But that symbolism has turned out to have huge political value. A dozen American states have already copied the EU’s emissions trading scheme, which was set up two years ago, forcing industry to buy permits to pollute. The White House has come under pressure not only from Democrats but from fellow Republicans such as Arnold Schwarzenegger and John McCain, both of whom are trying to enact legislation of their own.

And from businesses, which now understand that carbon has a price. They see European companies helping to clean up those in India and China, and some fear that they may lose out in the race to produce low-carbon technology. China has set itself national energy efficiency targets. And some think that India will become a global leader in clean technology just as it has been in antiHIV drugs.

The US is vital to bringing those other countries into the kind of international agreements that will be needed if the world is to heed the scientists. No one wants to wait for a different president. There are glimmers of hope. The White House is now talking up the actions of the pioneering states, rather than playing them down.

And the Intergovernmental Panel on Climate Change seems to have touched a nerve. Four hours after its report was released, the White House issued a statement defending President Bush’s record on climate change and replaying his remark of 2001 that the increase in greenhouse gases was largely due to human activity.

Angela Merkel, the German Chancellor, will be centre-stage of negotiations this year. As president of the G8 she is charged with bringing forward a global deal on climate. She is keen to show that Germans no longer need to vote Green to get green policies. She is also concerned about energy security. And it is still energy security that is uppermost in the minds of the leaders of the US, India and China, not the environment.

Downing Street is delighted by Mrs Merkel’s arrival on the scene because she seems to be a strong ally. The current EU scheme is weak, but it is doubtful whether it would exist at all had the British Government not set itself the most ambitious targets in the world for emissions reduction, and stood firm while other governments allocated far too many permits to pollute. This has helped the European Commission to put pressure on the most recalcitrant.

The onus is on the West to demonstrate that growth can be green. Otherwise developing countries are unlikely to follow suit. The IPCC report makes clear that altruism is not needed: action is in our self-interest.

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