The atheist, it has often been observed, is no less devout in his own way than the followers of the faiths he scorns: he is as sure there is no God as they are sure there is. Conservatives, likewise, in their zeal to debunk the "global warming" thesis, can be just as theological about their position as the prophets of doom on the other side. They even talk alike: where a tendency to use words like "biodiversity" and "ecosystem" has long been the identifying mark of enviro-wienies, it is as common today to hear conservatives babbling on about the latest data on atmospheric concentrations of "chlorofluorocarbons" and other greenhouse gases, and how there is no proof that these are "anthropogenic." Those of us who are, as it were, unsure whether we are agnostic might prefer to keep an open mind on these questions, perhaps hoping that in time all those excess greenhouse gases might escape through the hole in the ozone layer, and the whole tiresome debate will go away. Unfortunately, that option is about to be foreclosed. With representatives of more than 150 nations meeting in Kyoto, Japan in less than a month to negotiate limits on greenhouse gas emissions, we are forced to decide whose scare stories are scarier: the environmentalists, with their droughts and melted ice-caps and hordes of disease-bearing insects, or the conservatives, with their carbon taxes and lost jobs and trillions of dollars in lower incomes. The choice before us is stark: Either we fail to act now, and plunge the world into mayhem and catastrophe, or we act now -- and plunge the world into mayhem and catastrophe. As Woody Allen once put it, may God grant us the wisdom, and the courage, to make the right decision.

But then, we expect environmentalists to hyperventilate. What is more disconcerting is the sudden proliferation of alarmist talk from conservatives, they whose credo is supposed to be that there is no new thing under the sun, not even melanoma. The same people who calmly point out that the risks of dying from asbestos insulation in school buildings are less than the chances of being hit by lightning -- twice -- seem to have lost all perspective when it comes to legislated reductions in the amount of carbon dioxide in the air.

There's still room for skepticism about global warming, to be sure. Those who question whether the air is in fact getting warmer, or whether, if it is, the problem is man-made, or whether, even if both of these are true, it might not actually be a good thing on balance, are not, as the Prime Minister suggested the other day, in a class with the tobacco companies in their denial of the risks of cancer from smoking. There are still eminent climatologists on both sides of the debate, even if the majority would seem to favour the proposition that something suspicious is happening to the atmosphere.

But merely to say that we cannot be certain that global warming is a problem does not by itself make the case for inaction. I can't be sure that I won't be run over by a bus tomorrow, either. The question is whether the risk is worth the cost of insurance.

Let's take another recent example of a costly policy, with uncertain benefits: one that conservatives supported. When the Bank of Canada took action to reduce inflation, the short-term costs in lost jobs and lower incomes were certainly severe. Those who supported the policy had to concede that, while the great weight of theory and empirical evidence suggested that the costs of leaving inflation unchecked would grow over time, and in the limit could be catastrophic, we could not be absolutely certain of this. It's a judgment call.

So it is with global warming. If conservatives are worried that governments will take hasty action to reduce emissions, they needn't be. Even if the delegates at Kyoto do come to any sort of agreement -- a less than even- money bet at this point -- the most that they might be expected to do is to slow the increase in the amount of greenhouse gases in the air. If, for example, some version of the American position were adopted, reducing annual emissions to 1990 levels by the year 2012, the most optimistic scientists calculate the result would be to hold atmospheric concentrations of carbon dioxide at perhaps 450 parts per million, or about one-and-a-half times their pre-industrial levels. If it's a go-slow approach you want, that's what the world's governments are going to give you. If it turns out greenhouse gases are benign, there'll still be plenty of them around.

And the costs of this insurance policy? The worst-case scenario in a recent study by the Conference Board of Canada put the cost at 2.3 per cent of national output, spread over 12 years: instead of growing 30 per cent by the year 2010, the Canadian economy, groaning under the burden of emissions controls, would endure a meagre 27.7 per cent expansion. If more efficient approaches were used, the cost might be as little as 0.5 per cent of GDP. The case for inaction will have to get a lot scarier than that.