James Lovelock, inventor of Gaia Theory and godfather of the modern environmental movement, has finally renounced the green religion.

Climate alarmism, he says, is not “remotely scientific”; one volcano could make more difference to global warming than humans ever could; the computer models are “unreliable”; greens have behaved “deplorably”; and anyone who tries to “predict more than five to ten years is a bit of an idiot.”

Though this is not the first time Lovelock has rowed back on his earlier climate catastrophism – in 2012 he was already admitting “I made a mistake” – it’s his most emphatic rejection yet of the green litany.

Lovelock, 97, ascribes the dramatic change in his once fervently alarmist beliefs to the fact that he has “grown up.”

Only ten years ago – when the inventor, scientist and environmentalist was a mere spring chicken of 87 – Lovelock argued in his book The Revenge of Gaia that mankind was doomed.

Because of global warming, he predicted, “billions will die” and the few survivors would have to retreat to the Arctic which would be one of the few habitable places left on earth.

But now he admits to being “laid back about climate change.”

“CO2 is going up, but nowhere near as fast as they thought it would. The computer models just weren’t reliable. In fact I’m not sure the whole thing isn’t crazy, this climate change. You’ve only got to look at Singapore. It’s two-and-a-half times higher than the worst-case scenario for climate change, and it’s one of the most desirable cities in the world to live in.”

Besides, he says, nature is more powerful than the computer models:

It’s only got to take one sizable volcano to erupt and all the models, everything else, is right off the board.

Lovelock was speaking in an interview with the fervently alarmist Guardian whose interviewer Decca Aitkenhead was naturally somewhat taken aback by his views which she ascribed in part to his temperament as an “incorrigible subversive.”

But Lovelock himself insists that it is simply a question of looking at the evidence.

One experience that has sharply concentrated his thoughts is the cost of heating his home, an old mill in Devon. When the heating bills rose to £6,000 for just six months, he realised that he would have to downsize and has now moved to a smaller cottage on Chesil Beach in Dorset. This claim has brought him into conflict with another green guru, the chunky knit Guardianista George Monbiot.

“I remember George Monbiot took me up on it and wrote that it was impossible, that I had to be lying. But I wasn’t lying, I’ve got the figures.” Monbiot doesn’t quite accuse him of lying, in fairness; just of “talking rubbish” and “making wild statements”. In any case, he says that in the US he found he could heat a house for six months, in temperatures of -20C (-4F), for just £60. As a result, he has withering contempt for environmentalists’ opposition to fracking. “You see, gas in America is incredibly cheap, because of fracking,” he says. But what about the risk of triggering earthquakes? He rolls his eyes. “Sure enough, that’s true, there will be an increase. But they’re tiny little tremors, they would be imperceptible. The only trouble is that you can detect them. The curse of my life has been that I’ve spent a lot of time inventing devices that are exceedingly sensitive. And the moment somebody can detect something, they’re going to attach a number to it, and then they make a fuss about it.” He chuckles, then pauses. “I’m not anti-green in the sense that I’m in favour of polluting the world with every damn thing we make. I think we’ve got to be careful. But I’m afraid, human nature being what it is, the thing gets exaggerated out of all proportion, and the greens have behaved deplorably instead of being reasonably sensible.”

Besides Monbiot, Lovelock finds time for a little dig at yet another fervent green catastrophist the Prince of Wales:

He was once invited to Buckingham Palace, where he told Princess Anne: “Your brother nearly killed me.” Having read that Prince Charles had installed grass-burning boilers at Highgrove, Lovelock had tried one in his house. “It’s supposed to smoulder and keep the place warm; but it doesn’t, because it goes out, and clouds and clouds of smoke come out.” He giggles. “Princess Anne thought this was hilariously funny.”

His heretical stance on nuclear energy too is likely to alienate many of his former admirers in the green movement:

Even more heretical than his enthusiasm for fracking is Lovelock’s passionate support for nuclear power. But, like fracking, he says, it offers only “a stopgap” solution. “Because in the long term, they’ll use up all the uranium.” How long would that take? He pauses to do some quick mental arithmetic, as casually as I might tot up how many pints of milk to grab from Sainsburys. “Let’s see … I think uranium that is affordable to extract would last about 50 years, something in that range. It might be 100. When you’ve used all that up, you go to thorium, and that would last you three times as long as uranium – so, shall we say, about 200 years?” The most sensible energy solution would be to cover 100 sq miles of the Sahara in solar panels. “It would supply the whole of Europe with all the energy they needed,” but it won’t happen “because it would be so easy for terrorists to go and bugger it up”. So for now, nuclear energy is the only viable option.

Not that any of this matters much anyway, Lovelock suggests, because by the end of the century robots will have taken over and they probably won’t find much use for us.