“WHAT WOULD Jesus Drive?” is my favourite American bumper sticker, an unbeatable combination of earnestness and hypocrisy. If Jesus is a New Puritan, He presumably pedals a bicycle, revelling in slowing everybody down. If He is a Crunchy, he must drive a Prius, in an unbleached hemp shirt. If He’s an eco-apocalypsist, He’s on the hard shoulder with an “End is Nigh” placard, ignored by everybody.

It is fashionable to say that the doom-mongers have tapped into the superstitions of a credulous public. My colleague Matthew Parris put this beautifully last Saturday when he argued that “eco-apocalypticism runs powerfully with the grain of the collective human unconscious”. This is highly amusing to those of us who have waited ten years for anyone to take the slightest notice of climate change. There is an important truth in what Matthew says, but it should take him in a different direction.

Matthew suggests that the doom-mongers are gently crazy. That even the scientists are apt to screen out doubt, some in hope of boosting their research grants. That only scepticism is rational.

Well, scepticism is good. But not when the sceptics are saying that the only sensible course is to wait and gather more evidence. That’s not rational either.

Just because some greens are apocalyptic nihilists, because the whole climate change debate is riddled with prejudice, because the interactions of the climate are so complex that we will never fully understand them, does not make it rational to do nothing. Lord Lawson of Blaby argued in The Spectator last month that the potential effects of climate change may have been exaggerated and that the most “cost-effective” response is to adapt to changes as they emerge. No.

The Lords committee on the economics of climate change, of which Lord Lawson was a member, was critical of the science of climate impacts. Strangely, that did not prevent it from costing the economic consequences of effects that it said could not be determined. But let’s move on. For if you believe that a stable climate is a precondition for civilisation, it is priceless. If you believe that recent climate changes are even partly man-made, the only question is how to maintain stability.

Given that greenhouse gases accumulate in the atmosphere long after we have put them there, it makes no sense to wait until the fertile land has moved north or the Siberian permafrost has melted and released methane, the most powerful greenhouse gas, trapped beneath. The science is clear that such an event could tip us over into runaway warming. Measures taken today will have more impact than measures taken tomorrow. We should apply a lower discount rate and invest now.

An awful lot of intelligent people are devoting huge effort to selective fact-picking to support their prejudices. The problem is that we have not been here before. In war we mobilise our resources against a visible enemy. With climate change the enemy is not visible. The potential villains and victims are the same people. So we try to orientate ourselves by demonising each other. The NGOs rail against capitalism, trade, America, that have lifted millions out of poverty. The climate sceptics demonise the greens as wanting to wreck the economy. This is getting us nowhere.

We need a New Rationalism. One that considers what to do in the face of an unquantifiable risk of irreversible change. You don’t do a cost-benefit analysis before you go to war. The most peculiar thing about those who claim to be rationalists is their loathing of the assertion that so much of recent climate change is man-made. You would have thought they would be delighted, since that means we have a chance of controlling it. If we discovered that some asteroid was heading in our direction with a 5 per cent chance of collision, we would mobilise every missile, throw all our money at strategies to deflect it. But when scientists confront us with a threat that they believe is still within our control, we wish it away. Crazy.

Matthew Parris is right to point to puritans who don’t want people to find painless solutions. The greens who argue that everyone should have a carbon allowance are asking for a Soviet-style regime that is utterly impractical. We are not going to stop global warming by arguing for equity. What we need to do, right now, is everything we can to clean up the growth path of China, which is building one new coal-fired power station about every five days. We cannot deny the Chinese the chance to industrialise. We must give them more efficient combustion, carbon capture and storage, and pay the difference. Why have none of these so-called rationalists calculated how much this would cost, and set about raising the money?

They haven’t, because they don’t want to believe there’s a problem. Their capacity to ignore the warnings, the correlation between temperature and CO2 emissions, is fascinating. The real superstition here is our horror of using less, in societies that have been reared on consumption. There is a desperate fear that greater efficiency would devastate the economy. But the idea that we are plunging into a new Dark Ages is ridiculous. Is everything we hold dear threatened if we have to refit our homes with energy-efficient lightbulbs? In the US, corporations that have reduced energy use have made money.

What would Jesus drive if He were a New Rationalist? I don’t think he’d keep driving in the dark. He’d leave the car at home and take the train as often as possible. And He’d pay into a fund to help to clean up China.

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