John Rentoul: Now the reckoning. It will hurt

It is time to end the displacement activity of hating 4x4 drivers

"Act now. Act now. Oh God! I look at my guilty face in the shaving mirror as my children clatter down to breakfast - it's too late to act." The words were written in 1970 by that largely unrecognised prophet of the green religion, Stanley Johnson, father of Boris. Andrew Gimson quotes them in his richly entertaining biography of the Conservative higher education spokesman (so rich indeed is the entertainment that Boris Johnson apparently offered Gimson £100,000 not to publish). Stanley is a passionate, if avowedly hypocritical, environmentalist. In a polemical study of the problem of overpopulation, Life Without Birth, he admitted that he had not practised what he preached. He was already the father of three children, and would soon have three more. "How can I face that row of small blond heads bobbing over the cornflakes?" he asked himself with a typically Johnsonian flourish.

Well, we are all looking in the mirror now. Except that very few of us are as honest as Stanley Johnson about what we see. Last week's Stern report was widely described as a turning point, not just for the Government or the country but the world. That is quite a billing for an economic treatise written by a second permanent secretary at the Treasury, the aptly named Sir Nicholas Really-Quite-Puritanical.

Yet the Stern report has been greeted by a warm green consensus that is about as intellectually rigorous as mushy peas. It seems to consist of an optimistic assumption that simply describing the scale of the problem and saying that tough choices will have to be made will be enough to conjure the solution. That fails to deal with quite how difficult some of those choices are.

If you say, as the Prime Minister does, that climate change is "the most important issue that we face as a global community", then quite a lot follows - not all of it palatable.

Exhibit one: nuclear power. If global warming is so serious, the green calculus changes. Of course terrorists might attack a power station, and storing waste for 10,000 years is a huge problem. But if climate change is an emergency, we cannot phase out a low-carbon source of one-fifth of our present energy consumption. However much we reduce our use of carbon fuels, keeping nuclear power means we can burn even less.

Exhibit two: electric cars. They are not green. Any car that needs to have its battery charged from the mains puts more carbon into the atmosphere than a petrol model. Electricity is generated mainly by burning carbon fuels, and the transfer from power station to car battery wastes most of it. Even a Toyota Prius, the car of choice for rich greens and Government ministers, which uses the energy generated by braking to charge batteries to supplement the internal combustion engine, is no great green breakthrough. A recent study suggested that its total carbon cost over its lifetime is greater than that of many normal cars.

In fact, all the tough choices required to curb global warming involve complex trade-offs that are difficult for individuals or governments to judge. The trouble is that the mushy peas are infused with prejudice - and I do mean prejudice. There is a phenomenon abroad that might be described as green rage, a disproportionate righteous anger directed at the drivers of 4x4s. A Greenpeace internet video called "What does your car say about you?" displays a shockingly vindictive spirit, to take just one example. It shows a man shunned by his colleagues at work, who spit in his coffee, because, as you discover in the final scene, he drives a monster truck.

But this kind of bullying is not directed at people who drive low-slung, large-engined cars, or those who fly long distances, burning the equivalent of some years' driving in a single day.

These inconsistencies are bizarre. What is needed is not prejudices against particular kinds of car or lifestyle - or in favour of other kinds - but a price mechanism that allows people's individual choices to produce the best low-carbon outcome across the economy as a whole. If carbon fuels were taxed so that solar power became competitive, for example, we could afford to store all our nuclear waste in gold, jewel-encrusted caskets on the Moon. That kind of policy - green taxes to raise the price of carbon - is difficult for many greens, who tend to think of market forces as the problem rather than the solution. But at least greens understand the urgency. The more fundamental issue is that democratic nation states are a cumbersome mechanism for mobilising global action. We have seen spasms of green politics before. In 1987 the German Social Democrats fought an election on a platform of shifting the burden to green taxes - and lost. Middle-class voters sometimes go green in some places at times of prosperity, such as in Britain in the 1989 European Parliament elections, but it rarely lasts.

This time in Britain things could be different. Not because of the Stern report, although it helps, but because of David Cameron. Cameron's conversion to the green cause has moved the boundaries of the possible. In the years BC, Before Cameron, a pale-green Labour government could not take risks with those tough choices because William Hague would leap in to hail the fuel protesters as "fine upstanding citizens".

Now, in AD, Anno Davidii, Cameron has given David Miliband, the Environment Secretary, the space to push at the boundaries. Tony Blair and Gordon Brown emphasise the importance of international negotiations - and they are quite right that the US, China and India have to be persuaded. Britain produces only 2 per cent of global carbon dioxide emissions. But Miliband boldly made the case for unilateral British action in a speech preparing for this week's talks in Nairobi: "Imagine the extra leverage and influence we would have if we could go into negotiation not just as advocates for change, but exemplars."

Stirring stuff. But who will vote for politicians who build more nuclear power stations, put up taxes on flights, and make domestic gas and electricity more expensive - primarily in order to set an example to the world? It is time to end the displacement activity of hating 4x4 drivers and look at ourselves in the mirror.