Don't let a new Heathrow choke the life out of us

Once it seemed like a routine technocratic decision: long before the consultation was concluded, ministers spoke about the plan for Heathrow's third runway as if it were a done deal. But over the past few months it has turned into a major electoral liability. Thousands are packing into rallies and public meetings. Mild and law-abiding citizens are pledging to chain themselves to bulldozers. Protesters have swarmed onto runways and occupied the roof of the Houses of Parliament. The future of the airport has become one of London's most fiercely contested issues.

I think the turning-point for many people was the realisation that we had been lied to. In March, The Sunday Times unearthed documents showing that the Government had been colluding with BAA, which runs Heathrow, to rig figures on air pollution and noise that were presented to the public in the consultation document on the third runway.

Having discovered that it was impossible to build the runway without breaching legal limits, the Department for Transport "re-forecast" the effects of the new development, using figures provided by BAA. As if by magic, it discovered that building what is in effect a whole new airport at Heathrow would cause no adverse environmental impacts. The figures were false and, as the documents show, the Government knew it.

This is the fourth time in recent years that the British Government has misled voters over expansion atHeathrow. First we were promised there would be no fifth terminal. Then we were promised that there would be no third runway, and that the number of flights from the airport would be capped at 480,000 a year (a third runway will raise them to more than 700,000). Ministers seem prepared to tell any lie and break any promise to force this development through.

It is not hard to see why the Government initially refused to publish maps of the flight paths to and from a third runway. When local authorities in London drew up their own maps, they found that the noise zone from Heathrow would expand northwards to cover much of London and westwards across several counties. Estimates by the Heathrow Association for the Control of Aircraft Noise suggest that the new runway will cause a 300 per cent increase in the number of flights over south-east London. To complete the misery, the Government also proposes to end the "alternation agreement" which regulates flights at Heathrow's existing two runways, under which planes leaving the airport switch directions at 3pm to give west Londoners a break from the noise.

Even before a new runway is built, nitrogen dioxide pollution around Heathrow breaks the legal limits the European Union will impose from 2010. The Environment Agency warns that the pollution produced by a third runway - which can affect people's breathing - "will result in increased morbidity and mortality impacts". In other words, more people will die.

The impact of a new runway would be felt all over the world, too, because of the growing role of the aviation industry's CO2 emissions in climate change. The Department for Transport expects the number of passengers passing through British airports to rise from 228 million in 2005 to 480 million in 2030. It has instructed 30 airports to publish " master plans" to accommodate this growth. At the same time, ministers say they intend to cut carbon dioxide pollution by either 60 or 80 per cent between now and

2050. It is impossible to see how these two policies can be reconciled.

If we use the Government's conservative figures for the carbon dioxide produced by this expansion, and take into account the other greenhouse gases planes produce and the fact that 70 per cent of the passengers using our airports live in the United Kingdom, we find that aeroplanes alone would be responsible for 91 per cent of all the greenhouse gases the UK should be producing by 2050 - even if the Government adopts its lower target of a 60 per cent cut. If we use less conservative figures produced by researchers at Manchester Metropolitan University, we discover that aviation's greenhouse gas emissions would be up to two and a half times the total the Government says the UK should be producing in 2050.

Ministers tackle this minor inconvenience with another sprinkling of magic dust: carbon trading will solve it, as airlines can buy absolution from their environmental sins in the form of pollution credits from other industries. But how will this work if planes are producing more greenhouse gases than the entire economy is supposed to generate?

The transport secretary, Ruth Kelly, also argues that if Heathrow (which is already the busiest international airport on earth) is not expanded, the extra capacity will be built in another European country: "The flights and routes it operates will simply move elsewhere. It will make us feel pure but with no benefit to the rest of the planet." This is a position of craven moral surrender. Faced with a global environmental crisis, faced with rising misery for the people of London, we need leadership, not this shirking of responsibility.

Perhaps the Government's cowardice can be turned to good account. The strength of public feeling seems to have taken ministers by surprise. With more than 10,000 people expected at the Make a Noise demonstration at Heathrow on 31 May, the issue will become hotter.

The third runway's flight maps can also be read as a map of political hazard: the threat to the quality of life of the people living under the airport's shadow is so great and the fury at the way in which they have been misled is so potent that - in a tight general election - a decision to build a third runway at Heathrow could help to unseat this government. Ministers might rig the figures on pollution and noise levels and spin the numbers on climate change. But they can't escape the political arithmetic.

George Monbiot is the author of Heat: How to Stop the Planet Burning (Penguin, £8.99). He will speak tonight at the Evening Standard debate: Does London need a bigger Heathrow? at the RSA with Secretary of State for Transport, Ruth Kelly.