Much has been said, in recent weeks, about global warming. We need to act Now!, scream the politicians. The scientists have reached consensus on this issue! The Earth is warming catastrophically! Human civilization is responsible for this catastrophe! It's the biggest problem facing us! And if we don't start spending lots and lots of new tax money and making lots of new regulations right away, the consequences will be terrible! Terrible!

But why should we believe any of this? These scares come from the same bunch of politicians and media that gave us Saddam Hussein's weapons of mass destruction, ready to be fired at us within 45 minutes. We were right not to believe them then. So why should we believe them now? And why should we believe Nicholas Stern or anyone else, however well qualified, if they have been hired by the politicians to cry doom?

Meanwhile, quietly, scientists are working at better understanding the climate. And a lot of what they come up with doesn't match the hype. There is no consensus even about whether or not there is a real problem. There is strong suspicion of doctoring of data and mis-use of statistical techniques by some of those trying to make out that there is a problem. But views based on the facts only rarely find their way into the mass media. And when they do - as in Christopher Monckton's articles last month in the Sunday Telegraph - the politicians try to make out that people with such views shouldn't be allowed access to the media. There has even been talk of "Nuremberg trials" against scientists who deny the official scares.

You would have thought - would you not? - that, in Western societies supposedly based on the rule of law, our civilization would be allowed a full and fair trial. That every link in the chain of accusations would have to be proved beyond reasonable doubt, before any action was taken that could damage our prosperity or our freedom. That those that want to take such action should have to prove that there is a clear long-term warming trend, caused by carbon dioxide from human activities and not by things outside human control. That such warming would indeed lead to the catastrophes they claim, like large sea level rises and more droughts, floods and hurricanes. And that the economic effects really would be as bad as they claim.

Furthermore, if there has been doctoring of data or other dishonesty by some of the scientists involved, or by any of the politicians, wouldn't you expect action to be taken against them? If a witness knowingly lies or misleads in a court, that is perjury - a very serious matter.

You would have thought, too, that if our civilization were to be found guilty on this charge, any actions proposed must not impose any more costs or hassles on us than absolutely necessary. And we must be certain that they will make a big enough difference to future temperatures to fix the problem for good within, say, 50 years.

But no. We and our civilization are being tried by a kangaroo court. Whatever the facts are, however innocent we are, we are still to be found guilty. And punished.

The problem is, that politicians and their cohorts aren't interested in facts or in science. At best, they are only interested in people's perceptions. At worst, they are interested in nothing but the exercise of power on any excuse they can find. And that's what they are doing here.

The agenda behind the warming foofaraw is clear to those who can see. The politicals have found a good-sounding excuse to impose more and more burdens on us. All the main political parties are in on it, along with the usual suspects that forever demand increases in state power.

But many people can't see what's going on. Why not? One, because they let themselves get emotionally caught up in the scares. And two, because the global warmers have invented a very plausible-sounding rationalization, which makes it sound as if what they are doing is for everyone's benefit. That rationalization is called the precautionary principle.

The precautionary principle is an elusive beast. There is no generally agreed wording of it. It has many different forms, but in essence, it says that if there is a risk of something bad happening, particularly to the environment or to human, animal or plant health, then action must be taken to avoid or minimize that risk. In short, "better safe than sorry".

Put in such general terms, the principle sounds uncontroversial, even benign. Yet, on examination, it does not fit well with our common-sense ideas of how to deal with risk.

In thinking about risk, we recognize two kinds: risk to ourselves, and risk to others. As far as risk to ourselves goes, each of us must make our own decisions. We do it all the time; just about everything in life involves some degree of risk. We judge, rationally or not, whether a particular risk is justified for us. And we either take the risk, or we don't. For example, every time we go in a plane, there is a risk it may crash and kill us. We weigh this up, consciously or not, against the gain we expect from making the journey. And most of us come out with the same decision; we get in that plane.

The precautionary principle is worse than useless to us in assessing risk to ourselves. For it would have us either avoid risks altogether, or focus on minimizing them. But a life without risks is, at best, the life of a vegetable. And a life spent focusing on risks is a paranoid one.

Risk to others is a more complex subject. Sometimes our actions may have negative consequences for others. Individuals are responsible for the consequences of their voluntary actions; and it may be that the harm, which an action causes others, exceeds what reasonable people will bear in a spirit of mutual tolerance. In such cases, in civilized societies, we will be required to compensate those we harm.

There are indeed good reasons to invest in minimizing a risk to others. If we go to put a new product on the market, for example, it is common sense first to try to make sure it has no bad side-effects. For compensation claims are damaging, not only to the wallet, but to the reputation as well. Rationally, we will invest in minimizing risk as long as the likely gain from reducing that risk exceeds the cost involved in reducing it. Beyond that point, we have only two decisions we can rationally make; we either sell the thing as it is and face the consequences, or we scrap it. If we used the precautionary principle, however, we would have to spend forever more and more to allay less and less likely, or less and less serious, risks.

And isn't the precautionary principle itself a source of risk? Are we sure there would never be harmful effects from its application? One thinks of the human lives lost to malaria through the banning of DDT. And can we be sure that it would never cause us to miss out on benefits in the future? One thinks of drugs like aspirin, and wonders whether, if discovered today, such drugs would be approved for use.

Can we be sure that the global warming measures won't impoverish us and so have a nett negative effect on human lives and health? Isn't it possible that the precautionists are actually increasing the risks we human beings face? And if so, shouldn't they be stopped? Now?