The Climate Change Bill marks a big step towards removing carbon emissions from the British economy over the next 40 years. The economic consequences of this are unknown but would certainly be huge. MPs should reject it.

Yet politicians of all parties are engaged in an auction of ever larger promises on the scale of carbon reduction. These threaten to take us from the realm of the unlikely straight past the implausible and on towards pure fantasy. The Bill would impose at least a 60 per cent reduction on 1990 levels. Opposition parties have been advocating 80 per cent. Recently Tony Blair suggested that emissions of the richer nations should fall “close to zero”.

Such drastic reductions in the use of fossil fuels and therefore huge increases in the cost of energy - in industry, for heating our homes and in our cars - would leave us all worse off. It would hit the poor hardest, for whom energy is a larger proportion of their income.

Implementing the Bill would also, in practice, mean the closure of parts of British industry, only to see them reopen in China and elsewhere. The UK contributes only 2 per cent of global emissions. Unilateral action by the UK, as required by this Bill, would be politically irresponsible and economically disastrous.

Back in the real world these targets are unlikely to be met. Our first priority should therefore be adaptation to global warming, should it occur, including spending more on sea and flood defences and on adaptation research, particularly on behalf of the world's poorest nations.

While we adapt - as mankind has always done - we can do further work, both on the science and the economics. Anybody who reads the science will quickly realise that many key issues are fiercely contested. There is no consensus. But the controversies about the science are puny compared with those about the economics. On this we are being asked to rely on the Stern review, described by William Nordhaus, of Yale University, perhaps the world's leading environmental economist, as “completely absurd”.

We need to draw together the world's best experts in this field, both critics and supporters of Stern, to do a better cost-benefit analysis. Meanwhile, we can start reducing carbon emissions by doing those things that increase economic efficiency and growth, rather than prejudice it. For example, we should start phasing out remaining carbon subsidies. The revenues raised should be used to reduce general taxation.

We do not yet know - on the evidence, nobody can - whether virtually decarbonising our economy would be the best course. We'd better find out before rushing to legislate.

Andrew Tyrie, MP for Chichester, is a former Treasury adviser

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