Up In Flames: Cameron's pledge to lead the greenest government ever

Johann Hari on an environmental disaster in the making

When David Cameron gazed into the dewy eyes of a husky and promised to lead "the greenest government ever", what did you think that would involve?

Probably not an attempt to sell off all our trees to logging companies. Probably not a decision to open up the coast of Britain to the deep water oil-drilling that worked so well in the Gulf of Mexico. Probably not the bombing of another Arab country because there would apparently be "terrible economic consequences [for] the price of oil" if he didn't, as the Foreign Secretary William Hague put it in a recent interview.

And you certainly wouldn't have expected David Cameron's latest plan. He has decided to convert us to a new energy source that seems, in the US, to have released cancer-causing chemicals and radiation into the water supply – and will unleash even more planet-cooking gases than coal. Trapped under very hard shale rock in Lancashire, there is a large amount of natural gas.

But it's impossible to get to unless you use a previously-verboten method called "hydraulic fracturing", or "fracking" for short. It's simple. You blast the rock with one to seven million gallons of water that has been combined with up to 596 rock-dissolving chemicals. This penetrates 800ft into the ground and causes something like a mini-earthquake, breaking the rock into thousands of pieces and allowing the gas out.

Where it's already being used, fracking has been accused of three fatal flaws: contamination of the water supply, contamination of the air, and contamination of the climate. Let's start with the water. When his home in the woods in Pennsylvania was designated as an area perfect for fracking, the film-maker Josh Fox went to meet other people whose land had been used this way.

The result – the film Gasland – was nominated for an Oscar. He started in a small town called Dimock, on the border between Pennsylvania and New York state. They had over 40 gas wells that used fracking – and after it began, the community there started to notice something odd. Their water caught fire. Literally. When it came out of the tap, the water smelled of gas – and when it got anywhere near a flame, it combusted.

In addition to fizzing and bubbling with gas, the water tasted metallic and looked brown. Pat Farnelli, a local woman, explained: "Everyone was sick, including me. Our stomachs were really playing up – we couldn't handle anything." Fox's film argues that only half of the waste water that goes into the ground comes back up.

A report by senior Democrats in the House of Representatives last week found that this waste water contains at least 29 chemicals that are known to cause or strongly suspected of causing cancer, including methanol, benzene, sulfuric acid and lead. None of this biodegrades. When the fracking companies came and assured the residents of Dimock the water was perfectly safe, they said they should try drinking a glass – and the company men refused.

Fracking has also been shown in the US to contaminate the air. Fox's film went to the town of Dish in Texas, where large chemical clouds sometimes form over the gas wells. The town's mayor, Calvin Tillman, said that when the clouds form, "most of the people in this community think they've just taken their last breath". He commissioned an independent scientific analysis of the clouds – and it found "amazing and very high levels of known and suspected human carcinogens and neurotoxins", including one carcinogen that was at 107 times the safe level. The film-makers asked the companies involved to comment on all these allegations and they declined to do so.

The chemicals that have been found in the fracking waste include glycol ethers. Its known effects on humans include testicular toxicity, malformation of embryos, bone marrow depression, and destruction of red blood cells. Dr Theo Colborn, who has been named Time magazine's environmental hero of the year, warns: "The workmen are inhaling these chemicals round the clock, 24/7."

But this isn't the worst thing about fracking. More than any other popular fuel source, shale gas destabilises our planet's climate – driving catastrophic warming, sea-level rise, and increased extreme weather. Until recently, it was thought that this natural gas was "cleaner" than other fossil fuels when it came to global warming.

But a bombshell study by three professors at Cornell University, published in the prestigious peer-reviewed journal Climatic Change last month, found that the process of fracking releases so much methane – one of the most potent warming gases – that it could be as much as 43 per cent worse than coal. (The US fracking companies are refusing to co-operate, so the authors stress it's hard to be absolutely precise with figures.) The early green champions of shale gas have, in light of this evidence, recanted.

Everybody involved in the study of the downside of fracking stresses that it is at an early stage in its investigations. This is not a totally settled view, in the way that (say) the evidence for man-made global warming is accepted by virtually all scientists. But all this suggests there are very significant environmental risks that should make us think twice before rushing in.

The company engaging in fracking off the coast of Blackpool, Cuadrilla Resources, seems to believe there is no danger at all to the public. Its chief executive Mark Miller told MPs at the Energy and Climate Change Committee: "We're not really using unconventional technology. Shale gas exploration techniques, including hydraulic fracture, are conventional and have been used across the oil and gas industry for many decades. It is the reservoir source in which the gas is found that is unconventional."

He said it would be "near impossible" for any leak to occur, but then added that, if it did happen, it could be fixed within three to five days. Yet even the sober Financial Times quotes an analyst warning there is a "Toyota-sized reputational risk" associated with potential pollution from shale gas. Two days ago, France announced a ban on fracking, saying it is unacceptably dangerous.

So why is Cameron doing this? The easy, safe sources of fossil fuels have all been burned up by now. The ones that remain are in dangerous places – whether it's the soil beneath Libya, or rock that has to be dissolved with a potentially carcinogenic cocktail off the coast of Blackpool. The flaws of nuclear power have also been horribly exposed in Japan. That's why the US is expected to depend on shale gas for 45 per cent of its energy needs by 2035, with Britain trailing obediently behind – a terrifying prospect for the climate.

It doesn't have to be this way. Britain could instead be leading the world in showing how an advanced society can be powered by the awesome force of renewables – the wind, the waves and the sun. These are job-intensive industries that will dominate the 21st century, as the fossil fuels run out and throttle humanity. We could have the head-start on a better path, and become the global experts. Instead, we are bombing and drilling for the dirtiest fuels.

You might remember that David Cameron added a wind turbine to his house before the election. I warned then that it was a PR gesture – the Tory leader had dismissed wind turbines as "giant bird-blenders" only a few years before. But I didn't see quite how cynical it was. If Cameron had wanted to alert the public to what he would really do on the environment in office, he should have bombed his house to get cheaper oil – and then slathered a cocktail of chemical-sludge into the ground in the hope of hitting gas.