Chris Huhne: We must monitor carbon targets annually

The idea behind the Climate Change Bill that will be announced today is simple: we need a framework to help us to sustain a decades-long march towards a carbon-free economy. Coal, oil and gas must be phased out, or the carbon they emit must be captured and stored safely underground, if global warming is to be halted.

This will be a profound technological revolution akin to the shift from steam to petrol engines, or from gas to electric light. Yet this time, change must be driven by our survival as a species on this planet, not the desire to meet new consumer demands. That is why the policy framework has to be robust in order to strengthen our political willpower should it begin to flag over what will be a long haul.

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The Climate Change Bill must set an overall target to reduce carbon emissions each year so that the cumulative total adds up to cuts of at least 60 per cent by 2050, and probably much more. The Bill must also allow for that figure to rise sharply if that is what the science tells us is necessary. Our emissions must be guided by what is needed to make our planet habitable for our children and grandchildren, not by the soft option or the politically convenient.

All the main parties agree that there should be a climate change commission or carbon committee to assess progress and report to Parliament every year. In the Liberal Democrats, we want this body to be composed of those with obvious authority on the scientific and policy aspects of the problem, together with strong independence of mind. They need to tell it like it is without fear or favour, and should not just be nominees of the Government, whose efforts they will assess, but should be vetted and approved by both Houses of Parliament.

Since the commission will make an annual assessment, it should be clear about the criteria against which government policy - or our progress as a society - is measured.

There must be annual targets consistent with the long-term target, but of course those benchmarks should be adjusted to take account of short-term fluctuations in both the business cycle and the weather.

After all, the commission can assess progress after the year is over, and need not forecast. A year with sagging growth and hot weather would flatter our carbon efforts, and the commission needs to allow for that. Similarly, a cold snap should not disguise real progress.

The Government's view that annual targets are just too difficult is nonsense: they are in principle no more difficult than annual targets for inflation. It is too convenient for ministers to set targets against which their efforts can be measured only once every five years, when the typical term of office is only four years. These would be Nimto targets - Not in My Term of Office targets - and would not be worth the paper they were written on. We have to do better.

Beyond the Climate Change Bill, though, we will need Labour and the Conservatives to be as brave as the Liberal Democrats in coming up with hard proposals for change: so far, only the Lib Dems have put forward firm plans for greener but not higher taxes, by switching the tax burden from good things like work, risk and effort to bad things like pollution.

Without green taxes to shift our cars to lower emission models, and to limit the growth of aircraft greenhouse gas emissions, no climate change policy is worth the name. If we are to meet our climate change targets, we need to tax pollution, not people.

On cars, we have proposed a steeply rising vehicle excise duty on new cars so that the bottom two bands - including vehicles like the Toyota Prius - would pay nothing while gas-guzzlers in band G would pay £2,000 a year. Polling shows that more than two thirds of new car buyers would shift to more sustainable models with these incentives and the industry would also respond by bringing in leaner models.

On flights, we would base national tax not on passengers but on emissions, encouraging full flights and more fuel-efficient aircraft. Targets and annual assessments are needed to keep us on track in the long term, but if targets were the way of resolving problems, this would be the best governed country in the world (and it is not). The time for rhetoric on this greatest challenge of our age has now passed, and serious plans to tackle carbon emissions are overdue.

As Sir Nick Stern showed, we cannot afford to delay for the sake of our businesses and our economy as much as our environment. A change delayed is a change made more costly, and the countries that face the reality of climate change will be the winners in the post-oil age.

The writer is the Liberal Democrat environment spokesman