alligator crossing
© Telegraph UKLord Stern predicts that global warming will make the Arctic an ideal habitat for alligators

How come "the world's leading expert on climate change" doesn't even know how much carbon dioxide there currently is in the air, wonders Christopher Booker.

Confronted last week with the unfolding horror story of the Budget, we might have been grateful for the light relief provided by Lord Stern of Brentford, who told us how, unless we halt global warming, we can look forward to the sight of alligators gambolling at the North Pole, and Florida and Bangladesh sinking beneath the sea.

Since he produced the 570-page Stern Review in 2006, which Tony Blair described as "the most important report on the future ever produced by this Government", this former Treasury official and chief economist to the World Bank has won extraordinary adulation. In the US Congress he is acclaimed as "the world's leading expert on climate change", vying with Al Gore to be the world's Scaremonger-in-Chief.

Today Lord Stern is head of the LSE's Grantham Research Institute for Climate Change and the Environment, launched by a billionaire investment manager to advise on the fast-burgeoning global market in every kind of "low carbon technology", "emissions trading" and all the other growth areas associated with the climate change industry. Last week he was in the news for launching his new book, A Blueprint for a Safer Planet: How to Manage Climate Change and Create a New Era of Progress and Prosperity.

Unsurprisingly, there is no one for whom Lord Stern has more contempt than those he calls the "deniers" of man-made global warming. He told The Daily Telegraph last week that they "look more and more like those who denied the association between HIV and Aids, or smoking and cancer". In his book, he criticises the media for giving any space at all to such people, when "the balance of logic and evidence is 99 per cent or more to one".

But for a man whose whole case rests on the damage supposedly being done to the planet by carbon dioxide, it was somewhat disconcerting to see him quoted as saying that CO2 levels in the atmosphere have now reached "430 parts per million [ppm]". He said exactly the same last year in an interview with Prospect. The actual level is 388.97 ppm. It may seem a tiny point, but one might have expected "the world's leading expert on climate change" to have a rather surer grasp of a fact so central to his case.

Similarly, one would not expect a man whose institute is claimed to be "a world-leader in low carbon technologies" to claim, as he does in his book, that by next year wind energy "is set to account for 8 per cent of electricity generation in the UK", when the current figure is scarcely 1 per cent; or that "wind accounted for 35 per cent of total installed power capacity in the US in 2007", when two minutes on the internet could have shown him that wind power that year generated less electricity in the US than a single large coal-fired power station.

In fact, when the Stern Review came out in 2006, predicting that global warming could soon account for the extinction of 40 per cent of all species of life on earth, far from being universally lauded it was savagely criticised by some of the very people who might have been expected to praise it - his fellow economists. No one was more excoriatory than the man on whose work Lord Stern claimed to have based many of his most scarifying predictions, the noted Dutch economist Dr Richard Tol.

Far from being a global-warming sceptic, Dr Tol has played a key part in the UN's Intergovernmental Panel on Climate Change and wrote the UN Handbook on Methods for Climate Change Impact Assessment. But he could not have been more withering about the way the Stern Review went out of its way to cherry pick the most alarming possible predictions about the impacts of climate change and then to exaggerate them still further. Where Tol had, for instance, given a range of costs up to $14 per ton of CO2, while saying that the actual cost was "likely to be substantially smaller", Stern had more than doubled his figure, to $29 a ton. Stern's report, Tol pronounced, could be "dismissed as alarmist and incompetent", and his doomsday prophecies were simply "preposterous".

Yet this is the man, reverentially treated by the BBC, the media and politicians everywhere as "the world's leading expert on climate change" - so lost in his apocalyptic dreams that he doesn't even know something so basic to his cause as how much CO2 there is in the air we breathe.