Johann Hari: Cameron's conversion to environmentalism is little more than trendy food and hot air

In his first speech as leader, he said: 'I want to build more roads - we need a programme of road building'

Who would have thought that one day a Tory leader would urge the British people to "get on yer bike" and the left would offer a cautious round of applause? David Cameron is setting an example today by whirring on his BMX to the Soil Association to deliver a speech in praise of organic farming. This is just the latest stage in a long, deliberate campaign to green-wash the blue benches of the House of Commons. From grilling Blair on global warming to bragging that his new house has solar panels, Cameron's message to Middle England is - don't panic, I'm organic.

My initial reaction was that, in the middle of a global emergency, you take allies wherever you can find them. The environmentalist Mark Lynas recently explained the stakes in the game of climatic roulette we are all currently playing: "251 million years ago, the world warmed by 6 degrees Celsius in the space of less than a century. The result was that more than 95 per cent of the species on the planet died. The International Panel on Climate Change [the UN body made up of the world's leading climate scientists] predicts a rise hitting 5.6 degrees Celsius during the 21st century."

This shouldn't be a left-right issue: the Tory shires won't escape the disastrous unravelling of our climate, and nor will the corporate CEOs for long.

But then I began to look for substance behind Cameron's rhetoric. He militantly opposed one of the few measures the Government has introduced to ensure we meet our Kyoto targets: the Climate Change Levy that places an extra tax on the greenhouse gas emissions of big business. He still dismisses it as "red tape". Suspicious.

And then, in his first speech as party leader, he declared: "I want to build more roads ... we need a concerted programme of road building." Nobody asked how a hundred Newbury by-passes and vastly increased traffic fit with his supposed commitment to hold down greenhouse gas emissions.

It gets worse. The media fawned when Cameron appointed the aspiring Tory MP Zac Goldsmith to his policy review. But just because you buy the Ecologist magazine and a toy farm with the £300m you inherited from your tycoon father doesn't make you a serious environmentalist. Goldsmith is a fierce opponent of both wind farms ("they're ugly") and nuclear power, and has long sneered at the Green Party. His only proposal to meet our Kyoto targets - never mind the far more ambitious targets we need to achieve if we are going to avoid disaster - is to reduce energy waste. He believes that loft insulation, not leaving electrical appliances on standby and other small measures could cut Britain's energy use by 60 per cent.

Yes, that's 60 per cent. I am all in favour of an urgent programme to cut waste, but this is an unserious, glib proposal, like so much of Goldsmith's "thinking". If he was not the pretty Old Etonian son of a fantastically rich man, Goldsmith would struggle to get a job as Number Two on the environment desk of a local paper. If he is going to shape the Tory policy on global warming, then we will be worse off even than under Tony "I'm-changing-my-thinking-on-Kyoto" Blair.

Goldsmith's reputation for environmentalism stems from his adoption of a trendy lifestyle greenery that is - at best - a distraction from the ongoing global crisis. Cameron's decision to address the Soil Association today in praise of organic farming is a perfect example of this.

The idea of organic farming was created in the 1920s by Rudolph Steiner, a mystic who said crops should be planted not with chemicals, but according to the signs of the zodiac. He believed there was a mystical force emerging from the centre of the earth - and radiating down from the stars - that could make crops grow far better than "inhuman" mechanised agriculture.

Ah, but surely the organic movement has moved far beyond these anti-scientific roots? The man David Cameron will stand next to today and hold up as a model for Britain, the Soil Association director Patrick Holden, uses Steiner's techniques on his own farm in Wales, planting apples according to the movements of the moon and astrological signs. (Apparently, apples belong to the Leo star sign, presumably because of their fiery temperament and ruthless ambition.)

The hero and icon of the organic movement - Charles Windsor - champions this Mystic Meg approach to farming too, using your tax money and mine. Organic farming started as a faith-based position, and ever since, it has scrambled - without success - to find scientific backing for its claims.

At first, the argument for organic food sounds persuasive: isn't it better to use the things we can find in nature, rather than synthetic chemicals? But it doesn't take much analysis to see why this is flawed: after all, toxins occur naturally too. This becomes clear if you compare the way organic farmers deal with potato blight to the way science-based farmers treat it. Organic farmers use copper sulphate, because it occurs in nature. Ah, natural - and safe, right? Well, this organic copper sulphate has caused liver disease in vineyard workers, and it is so toxic that the EU theoretically banned it in 2002, but since organic farmers don't have any alternative, it is still being used.

In exactly the same situation, scientific farmers use synthetic copper. Boo! Hiss! Unnatural! But every single scientific study has found it to be safer and more effective than its organic twin. It's not hard to absorb this reality: after all, Sars and Aids are "natural" phenomena; paracetamol and AZT are "synthetic".

We certainly need tougher regulation of pesticides to ensure that dangerous chemicals such as DDT don't slip through. But there was an EU proposal to do just that last month - the Reach agreement - and Cameron's Tories opposed it as (how did you guess?) "red tape". To now go to the other extreme and promote farmers who are against using any synthetic chemicals at all is an incoherent and inconsistent over-reaction - like responding to the dangers of thalidomide by stopping pregnant women from taking any medicine at all.

Environmentalists have science on their side when it comes to the biggest issue in the world, global warming. Why allow that fact to be compromised by also advocating this hocus-pocus? The world's leading environmental science journal, Nature, made this warning recently, when it published a study of organic food that found it contains "very little science", is no better for consumers, and causes environmental disasters of its own because it burns up high levels of fossil fuels.

Nature concluded: "Organic agriculture was originally formulated as an ideology, but today's global problems - such as climate change and population growth - need agricultural pragmatism and flexibility, not ideology."

So far, Cameron has offered environmentalists nothing but a playboy airhead, some worthless New Age farming, and a road-building programme - while the world slowly, fatally warms. Now remind me again: why we were applauding his greenery?

j.hari@independent.co.uk