VOTE Blue, Go Green. Vote Brown and, it seems, you’ll Go Green, too. Vote Orange, Liberal Democrat that is, and you’ll probably go a nice safe shade of magnolia. But they promise you’ll Go Green, too.

Britain’s political establishment has signed up to global warming and the urgent need to stop it. David Cameron took the husky trail, hatless, to a Norwegian glacier to demonstrate his commitment to the cause. Gordon Brown used a trip to America to say last weekend that advanced economies have a “moral duty” to tackle climate change, and that everybody has a “personal and social responsibility” to act.

Sir Menzies Campbell hasn’t yet taken to a dog sled, or a bicycle for that matter, but he has promised to give up his Jaguar. Cameron and Brown are getting hybrid cars.

Many would say “hear, hear” to this and welcome evidence of so much political commitment to the planet’s future. As far as Defra (the environment, food and rural affairs department) is concerned, time is running out — it is the “greatest environmental challenge” the world faces. “Rising global temperatures will bring changes in weather patterns, rising sea levels and increased frequency and intensity of extreme weather events,” it said.

Sir David King, the government’s chief scientific adviser, is a chemist by training, not a climate scientist, but he was famously bold enough to say climate change was a bigger threat than international terrorism.

Most of us, I suspect, had quietly accepted the three central propositions of global warming, namely:

1. The world is getting hotter, and will do so at an increasing rate.

2. This global warming is due to an increase in greenhouse gases — mainly carbon dioxide but also others — in the atmosphere.

3. This increase in greenhouse gases is man-made, so we must reverse it, even if this means sacrificing growth.

I had certainly accepted most of that and rather scoffed at the global-warming sceptics. So, it seemed, had most scientists. The closer you look at it, however, the thinner the evidence is.

Richard Lindzen, professor of atmospheric sciences at Massachusetts Institute of Technology, will this week receive in Sweden the Leo prize for independent thinking. He stands out against what he describes as “climate change alarmism”.

Every freak weather event is blamed on climate change, he pointed out in a recent paper, Understanding Common Climate Claims. Some even blamed the Indian Ocean tsunami, a geological event, on global warming. He describes a “triangle of alarmism”, in which scientists make meaningless or ambiguous statements, advocates translate them into alarmist declarations and politicians respond to the alarm by feeding more money to the scientists.

On the central facts of the global-warming case, Lindzen notes the mean global surface temperature has increased by only 0.6 degrees (centigrade) in a century, during a time in which greenhouse-gas emissions in the industrial countries increased sharply. The sensitivity of the climate to greenhouse gases, he suggests, is a lot less than the alarmists suggest. As a rough rule of thumb, he argues, a doubling of greenhouse-gas concentrations in the atmosphere might result in a rise of 0.5C in average temperatures, while a quadrupling produces a 1C increase.

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