Man-made climate change may prove a disaster. No, I do not mean climate change itself. My concern here is rather over the policy responses.

For, as was predictable and predicted, recognition of the risks is generating a host of interventionist gimmickry, not least in the UK.

People I think of as my friends - pro-market liberals - are suspicious of what many of them consider the "man-made climate change hysteria". They are surely right to note that it is a remarkably convenient banner for opponents of the market economy, be they egalitarians or deep-green environmentalists. This time, they fear, Malthusians and socialists may have a politically successful (albeit, in their view, scientifically false) argument in favour of a long-standing desire to throttle the life out of the free-enterprise economy.

Lord Lawson, chancellor of the exchequer in the government of Margaret Thatcher, partly took this line in a lecture he delivered to the Centre for Policy Studies last November. I do not know what he thinks of David Cameron's adventures in the politics and policy of climate change. But I can guess.

Yet even if one accepts the validity of concerns about man-made climate change, one should agree that market liberals also have a legitimate concern. Instead of policies that are minimally intrusive, well-targeted and efficient, we are depressingly likely to get the exact opposite.

This is partly because many on the climate-change bandwagon do not want to leave the market economy intact. "Are you enjoying yourselves?" seems to be their question. "Let's find some way of stopping you." It is also because politicians have a strong desire to tinker piecemeal.

Since climate change is likely to be a concern over decades, it is essential to get policy right. The big rule, as always, is: keep it simple, stupid.

A good example of what many (though not all) economists would consider a mistake has been the decision to go for tradeable emissions permits whose prices have proved disturbingly unstable. Predictably, the adoption of such permits is already leading to proposals to create a carbon emissions budget for every individual. Predictably, too, this return to rationing is, in the UK, supported by rhetorical appeal to the egalitarian spirit of the Blitz (Mark Roodhouse, this page, March 13, 2007).

Yet the spirit of the Blitz, applied in the UK alone, will achieve just about nothing, since the UK is responsible for a mere 2 per cent of the global total. So what Mr Roodhouse and his ilk should call for is a global system of individual tradeable permits, to operate not just for a decade, but for the indefinite future. It is clear why an egalitarian with control-freak tendencies might welcome such a system of bureaucratic controls on most of humanity that this would require. But why should anybody else do so? And why should anybody believe it could be made workable?

Yet Mr Roodhouse is at least logical. He does also accept that his ration coupons should be tradeable. Meanwhile, Mr Cameron suggests that each individual might have some sort of "green air miles allowance", with a sliding scale of taxation on those who travel most. The difficulty of monitoring such travel would prove immense: one can already foresee the host of business people taking their flights from Paris. Mr Cameron is right that air travel should be included in the scope of taxation.

He is right, too, that the taxation of emissions should, other things being equal, replace other taxes, rather than raise the overall level of taxation.

But this is surely no more than a populist gimmick.

Then there is the government. In its new climate change bill, it proposes "a series of clear targets for reducing carbon dioxide emissions - including making the UK's targets for a 60 per cent reduction by 2050 and a 26 to 32 per cent reduction by 2020 legally binding". In this case, as I understand it, the government would be held legally liable for failing to compel the people of this country to behave as it desires over the next half century.

I find that frightening.

Meanwhile, in a typically wide-ranging speech this week, the chancellor proposed a raft of initiatives and incentives on light bulbs, efficiency standards, home insulation and micro-generation. It is impossible for the outsider to judge whether these would be cost-effective. Is the plan to make new homes "zero carbon" an efficient way to achieve emissions reductions? I have no idea. I suspect the government does not have any idea either.

Let us concentrate on the big issues: any workable policy system must be global; it must create stable incentives; it must be administratively simple; it must include investment in creation and dissemination of new technologies; and, not least, it must allow people to get on with their lives with as much freedom as possible. Uniform prices on emissions - ideally, through taxation - will do most of this job. Almost everything else is unnecessary or counterproductive.