Few people have realised it yet, but averting climate change is going to be as much about psychology as economics. The MPs on the Environmental Audit Committee believe that forcing airlines and other businesses to offer carbon offsets will make customers think more about their impact on the environment. So the businessman will still fly to New York, but the £10 he pays voluntarily may make him think twice about his other activities – while also paying for solar cooking stoves in Bolivia or forest protection in Brazil.

The danger is that human nature could turn out to work in precisely the opposite way. The very cheapness of offsets could make people underestimate climate change. And by paying an extra £10 for our flight or cab ride or gas-guzzling patio heater, we may simply feel free to keep on sinning.

I fear that the second is more likely. HSBC and Barclays are both described in this report as having increased their carbon dioxide emissions after introducing offsetting schemes. All government departments now offset – but walk around Whitehall at night and you will see that the lights are still on. That is why many environmentalists feel that offsetting is the modern equivalent of the guilt-absolving indulgences sold in the 16th century by the Catholic Church.

To be fair to the MPs, they have looked carefully for evidence of the impact of offsets on behaviour, and found nothing compelling on either side of the argument. They are calling for more research. They also state, quite rightly, that offsets should only be used for “unavoidable” activities, after a household or company has done everything possible to reduce its energy use. But who is to say what is unavoidable? In previous reports, the Environmental Audit Committee has emphasised the enormous potential of energy efficiency and stricter building regulations in tackling climate change. The fashion for offsets must not distract from those more humdrum but more effective policies.

This report raises important issues. Deforestation, it argues, is one of the greatest threats to a stable climate. We will probably have to pay other countries to avoid deforestation, but we must find the most robust ways of checking that we are getting what we are paying for. Such auditing problems beset both voluntary offsets and the carbon “credits”, or permits to pollute, which are traded in the EU carbon market.

But back to psychology. About 1.5 million Britons offset their flights last year. Ten per cent of people travelling with lastminute.com offset too. That is a substantial figure for schemes that are voluntary, and brand new. It is, in fact, a dramatic demonstration of conscience by individuals. Its popularity should be sending a clear signal to Government that the public wants decisive action.

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