scientist or meteorologist, but of an economist, and one who, by his own confession, had very few preconceptions about climate change.

Indeed, in a speech in Oxford earlier this year, Sir Nick explained that he had previously been agnostic. Up to July or August 2005, he "had an idea what the greenhouse effect was, but wasn't really sure". Over the following months, he said, he had become "convinced that this a really big and fundamental issue."

Because his training is as an economist with a profound interest in economic development, the Stern report has much to say about the impact of climate change on poorer countries. It is also a basis for policy making.

But there will be lively argument about the report's conclusions among economists, and especially

about the relatively low cost of taking action that the report calculates.

Moreover, although Stern's conclusions will clearly have the support of the British government, there will be plenty of problems in turning the recommendations into effective policy. Climate change is an awkward issue for governments to deal with, and not just because the costs fall on today's voters, whereas the pay-off accrues to their grandchildren.

In addition, Britain makes a relatively small contribution to climate change. The real question will be whether the Stern report will influence thinking in the United States, China and India. These three countries will, over the course of the next century, come to account for the bulk of global-warming emissions.

The report's main conclusions

See the trailer for Al Gore's climate change film, An Inconvenient Truth

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