He has certainly seen enough Treasury computer modelling over the years to recognise the limits of long-term forecasting, especially, as in the case of the climate, where our knowledge is still so fragmentary. To demand a specific set of responses which have huge socio-economic consequences now on the basis of a possible extrapolation of one set of variables centuries hence is not necessarily the most responsible option.

For instance, having plotted soaring temperatures in the last quarter of the 20th century, the models anticipated further increases in the first years of this century. Instead, Britain’s leading climate research facility at Hadley has recorded that the temperature has actually stopped going up. Having got it wrong, the models have been duly tweaked and anticipate a resumption of the upward trend after 2009. We shall soon find out if this proves correct.

Certainly, informed guesswork is better than uninformed guesswork. But we do need to be careful about long-term extrapolation from what may be short-term phenomena. After all, a study of the Atlantic Gulf Stream created alarming headlines when it noted a sharp weakening in its current. Subsequent (less publicised) studies suggest the weakening was actually well within the bounds of natural variation and is not a consequence of global warming. As for rising sea levels, the rate of increase may actually have slowed in the second half of the 20th century, rather than accelerated.

At any rate, the complicated picture presented by a constantly changing climate appears all too simple for our politicians. In Lawson’s opinion, the Stern Report was commissioned to back-up the British government’s preconceptions rather than offer disinterested information. He dismisses the variety of responses currently in vogue, from the ‘scam’ of carbon offsetting to the wild commitment in the Climate Change Bill to impose a statutory 60 per cent cut in Britain’s CO2 emissions by 2050. A simple carbon tax would at least have the advantage of transparency.

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