The calculation is simple. If you believe in God and live a God-fearing life, and it turns out there is a God, then, when the time comes, you’ll be rewarded with a place in paradise for ever. If there isn’t one, and you’ve lived the religious life, then you will end up, infinitely speaking, the same as everyone else, and no worse off than the atheist who spent his life deriding religious belief as superstitious nonsense.

But if you don’t believe in God and live a generally irreligious life, you’re taking one hell of a gamble. If it turns out you were right all along, and there’s no God and no afterlife, so what? You won’t even have the pleasure of a nanosecond of gloating at the ineffable stupidity of your God-bothering fellow ex-human beings. The very moment of your intellectual triumph and existential vindication is also the precise moment at which its significance collapses to literal nothingness. That will be it. Lights out. For ever.

But if it turns out there is a God, and you’ve spent your earthly span denying his existence and generally poking fun at believers you’re going to feel a bit sick when St Peter shows up on the other side, ledger in one hand and one-way ticket to the Underworld in the other.

Therefore, Pascal said, the sensible thing to do is to resist the atheist temptation. The best on offer is a lifelong sense of smug superiority in this world. The worst is eternal damnation. The costs of being wrong are so high that they would require a level of confidence in your unbelief that is humanly impossible. Why chance it? Pascal’s Wager, it seems to me, is a good starting point for consideration of climate change. Belief in global warming and its human provenance seems to have replaced traditional religion as the faith of the secular.

Politicians and the media accept the wisdom of climate-change believer with the same unquestioning devotion that medieval peasants and monarchs used to bring to the Church. Scientists predict earthly conflagration with all the confidence with which 17th-century divines used to caution about eternal hellfire.

For myself, I prefer the old religion, and count myself still a bit of an agnostic on climate change. Certainly, the evidence is clear that the earth has been getting warmer, and certainly the preponderance of scientific opinion is that our emissions of greenhouse gases have played at least a highly significant role in that.

But there remains enough doubt in there to merit a cautious agnosticism. Unquestioning faith in current scientific hypothesis opinion is not always rewarded with consistent conclusions (ask Pluto).

On this as on any other subject we agnostics don’t have the luxury of being hermits, whose philosophy is summed up in the injunction: don’t just do something, stand there! What are we actually supposed to do in a world of high uncertainty?

This is where our friend Pascal comes in. If we believe in global warming and do something about it and it turns out we’re right, then we’re, climatologically speaking, redeemed — if not for ever, at least until some other threat to our existence comes along.

If we’re wrong about it, what is the ultimate cost? A world with improved energy efficiency and quite a lot of ugly windmills.

If we don’t believe in global warming and do nothing about it, and we’re right, so what? Our distant posterity will be able to cite us approvingly in future opinion columns. But if our unbelief turns out to be unsupported by the outcome and we’ve done nothing about global warming in the meantime, then we’re in a position analogous to the atheist at the gates of heaven. We will spend not eternity, but perhaps the rest of the earth’s existence, ruing our folly.

Now there is one significant risk that makes this equation slightly different from Pascal’s. There could be high costs of believing in the human role in global warming and being wrong about it. We may have to trade off a lot of economic activity in the next 50 years to lower our carbon emissions.

It is certainly a risk. And yet these costs might actually be lower than is sometimes feared. Like virtue, improving energy efficiency is its own reward. Individual companies such as Wal-Mart are already discovering that the costs of reducing their carbon footprint are offset heavily by efficiency gains.

For whole economies the equation is not necessarily as attractive but there’s still reason to believe that efficiencies can reduce the long-term net costs of investment in alternative energy sources. There are, besides, other incalculable benefits of shifting our energy-use patterns — reducing our economic and strategic dependence on Middle Eastern oil, for one.

In modern game theory Pascal’s Wager is called the maximin criterion. When confronted with a choice of actions in conditions of uncertainty, the correct choice is the course whose worst outcome is least harmful. That puts the burden of proof on to the global-warming sceptics. Unless you’re really, really certain that we’re all going to be fine, then the only prudent course is to act now to reduce emissions. The costs of understating the threat are much higher than the costs of overstating it.

The wise thing to do, then, is to invest in alternative energy and change public policy so as to raise fuel emission standards and penalise overconsumption. Kyoto, of course, is a dead letter, but renewed efforts at international co-operation are also essential. If I were a betting man, I’d wager that old Pascal is, even now, smiling in agreement.

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