James Lovelock lives with his wife, Sandy, in an old coastguard's cottage less than 100 metres from Chesil beach in Dorset. To reach it, you have to drive along a rough, mile-long road, which in stretches has collapsed because of the winter storms that pounded the shingle spit. You must have had a devastating winter, I say when I eventually find the cottage. Not devastating, he insists, despite having been cut off by floods for four days, fascinating. Which sums up Jim Lovelock perfectly. The inventor/scientist/environmentalist is captivated by and curious about everything, which is why at 94 he radiates joie de vivre. He is the youngest 94-year-old you could ever hope to meet.

His new book, A Rough Ride to the Future, is part memoir of his long life in science and part prediction of whether humankind can survive. I had intended to ask him whether it was a final testament, but the question dies in my throat. He so obviously doesn't plan his life that way. He has mastered the art of getting old by not giving it a moment's thought.

The concept for which Lovelock is best known is Gaia – the idea that the Earth is a single, self-regulating entity in which the organic and inorganic interact to sustain life. He developed the idea in the 1960s when he was working for Nasa and has returned to it frequently; he says defending it from detractors is one reason he carries on writing. "I want to keep fighting the battle because the academics just won't buy it, whereas most other people have."

Lovelock, who for the past 50 years has been what he calls an "independent scientist" unfettered by institutional links, reckons he knows why academics reject Gaia. "It's political," he says. "You can't run a university unless it's divided into subjects. If you try and teach the whole lot, it becomes a complete mess and the vice-chancellor goes mad, so they have to divide it up. But if you divide it up, you can't understand it." Lovelock, who trained as a chemist but is just as interested in and likely to expound upon physics and biology, detests academic compartmentalisation. "The universities," he says, "have reached a point similar to the monasteries in the middle ages where the monks counted the number of angels that could stand on the head of a needle."

The thesis underpinning A Rough Ride to the Future is what Lovelock calls "accelerated evolution". He argues that Thomas Newcomen's invention of the steam engine in the early 18th century was as significant in evolutionary terms as the emergence of the first photosynthesisers more than 3bn years ago, ushering in an age in which human activity has had a rapid and profound effect on the planet. "The changes in the environment that we see as adverse – from rising carbon dioxide abundance, climate change and population growth – are," he writes, "all consequences of this new [evolutionary] inflation; as may be economic instability and the tendency of the human species to become city or nest animals."

He cites Moore's law, which states that a computer's processing power doubles every two years, and says we, too, will have to adapt to this speeded-up world. Man likes to assume he is the end of the evolutionary cycle, but dinosaurs, who held sway for almost 150m years, probably laboured under the same misconception. In the book, Lovelock posits the idea that one consequence of accelerated evolution could be that at some point we ourselves incorporate inorganic elements in our bodies. "Instead of robots going to war with us and taking over the world, which is the way it's always portrayed in science fiction," he says, "I thought, what happens if we join with them?"

Lovelock working for Nasa at the University of Houston in 1962. Photograph: Donald Uhrbrock/Time Life Pictures/Getty Images

I express a polite degree of incredulity, but he persists. "It's already happening. I've got a pacemaker, which is a very handy device and works like a dream. I'm beginning to regard it almost as part of my body, and don't think about it. My pacemaker is an old-fashioned one. It has a battery that lasts 10 years and has to be replaced, but already pacemakers are starting to be thought about that use the body system to provide the energy to keep them going. It's coupled to the physiology of my body more or less completely, and, much more sinister, it has a radio communication with the outside world so that the technician can check it every year to see whether it's working. This really bothers me, because I can see it's only a short time before my body's on the internet and receiving spam. Once you go in for this endosymbiosis with the mechanical world, you're in for trouble, and we've started."

Lovelock, who manages to be both playful and deadly serious at the same time, is almost converting me to the idea. "Computers are getting more and more organic all the time," he says. "They are being made from carbon, and I can envisage a process whereby an endosymbiotic person with these things in it will sufficiently fuse the two life systems together that it will become a single person that will breed true." I ask when this startling development might occur, but he prefers not to make a prediction. Cue further incredulity on my part. "Dash it all," he says, "we're pretty odd when you think that we started off 3bn years ago as single cells floating around."

If academics dismiss the notion of Gaia, how are they going to react to Lovelock's projection of robo-people? Won't they just dismiss him as a crank? "I'm sure some will," he admits, "but that's why I've always been an independent scientist." If he was part of an academic institution, he says, he would never be able to explore the wilder shores of science. He left the Medical Research Council in the early 1960s, when he felt it was becoming more restrictive. "I wanted to be free. I could see tramlines of security going on to retirement and the grave. It was very selfish and very stupid of me in many ways." Stupid because he was by no means wealthy, had four children, and soon after quitting his job his first wife was diagnosed with multiple sclerosis. But happily the US rescued him with offers of work at both Nasa and Hewlett-Packard, and his career as a freelance scientist-inventor was launched.

Lovelock's pursuit of freedom had begun even earlier. The son of working-class parents who ran an art shop, he grew up in Brixton, south London, "hated school like poison", and taught himself science from books in the local library. He says he wanted to be a scientist from the age of four when his father gave him a primitive electronics set, and reckons the sense of science as a vocation that motivated him has largely disappeared. "The whole system of teaching has lost it, because it's taught as if you were going into a career. It isn't a career and never should be. I've never had a career. One lives from day to day, and doesn't think about it too much. That's why at approaching 95 I don't think about ageing and death. I just think, 'What's the next job?'" Lovelock had a heart attack 30 years ago and has had surgery on 40 occasions since, so to be in such good shape at 94 is miraculous.

'Earth is as old as me in comparative terms. It doesn't have long to go' … James Lovelock. Photograph: Laura Jones/BNPS

Ageing is inevitable, and doesn't worry him in the slightest. "Everything's running down, so enjoy it while you can. It's not a gloomy thought at all. You wouldn't have energy to do things unless things were running down." He is thinking of planets as well as people. "Earth is about as old as me if you look at it in comparative terms. It doesn't have long to go. It could be as little as 100m years, though I think it's more likely to be about 500m. As things age, they become much more vulnerable to disturbance. If someone as old as me gets pneumonia, it'll probably kill me, whereas if you're young you'll shrug it off. It's the same with planets. If there was an asteroid impact as big as the one 65m years ago, it would be quite dodgy. The older a planet gets, the less capable it is of resisting such an event. Life gets more complex and more vulnerable to disturbance."

Shouldn't this news worry us? "Of course it shouldn't worry us. If we [as a species] are still around in 100m years, it would be amazing." He doubts whether anything resembling man will still be around, but even that can't dent his essential optimism. "I don't mind the thought that a hundred progeny from now I'll be unrecognisable," he says. There will, he reassures me, be a bit of us left in whatever emerges, just as the DNA of those first cells from 3bn years ago feature strongly in our own DNA.

Lovelock's new book is likely to be claimed by both sides in the climate change debate. He has pulled back from the alarmist predictions of The Revenge of Gaia, published in 2006, and now says the rate of global warming is slower than he anticipated. "I was a little too certain in that book," he admits. "You just can't tell what's going to happen." He says the oceans store most of the heat from the sun, tempering the impact on the atmosphere, and our lack of understanding of the likely effects of the warming of the oceans makes it very difficult to predict the long-term impact. "It could be terrible within a few years, though that's very unlikely, or it could be hundreds of years before the climate becomes unbearable."

Damaged reactors at Fukushima in Japan in 2011. Photograph: Air Photo Service/AFP/Getty Images

Won't this give succour to climate change deniers? "It's just as silly to be a denier as it is to be a believer," he says. "You can't be certain." He says climate change scientists should adopt the same level of statistical stringency as exists in medicine. So we need to take the politics out of climate science? "Oh sure, but we're tribal animals. We can't help being political."

I suggest to Lovelock, who dislikes the fetishisation of eco-causes, that he has a complicated relationship with the environmental movement. "Not really," he insists. "I'm an old-fashioned green, a person who's happy with that Selborne character, Gilbert White [the 18th-century parson, writer and pioneering naturalist]. I'm very old, and the British countryside up until world war two was glorious. It was heathland all the way from London to the coast, and you could walk everywhere. Humans and the countryside were in a wonderful equilibrium. We were just another animal in the place, but it got wrecked with the coming of cars."

Lovelock sees environmentalism today as a form of what he calls "urban politics". "It's become a religion," he says, "and religions don't worry too much about facts." He is an enthusiast for nuclear power, which makes him unpopular with many greens. "I'm a scientist and an inventor, and it is absurd to reject nuclear energy," he says. "It all comes from the religious side. They feel guilty about dropping atom bombs on people. Here was this extraordinary gift given to humans – a safe, cheap source of power – and it gets horribly abused right at the start. We're still playing out the guilt feelings about it. But it's sad because we in Britain could now be having cheap energy if we'd gone on building [nuclear power stations]."

Nuclear waste? "It isn't a problem," he insists. "Sandy and I were invited to France, and we stood on 25 years of nuclear waste at La Hague. I had my own handheld monitor to check whether they were bullshitting me about it, and it was showing about the same reading as I was getting in this room. It was completely safe. The Swiss did a study of the number of deaths per year in all the various power systems, and nuclear beats everything." What about the meltdown at Fukushima in 2011? "That's the most amazing collection of lies ever known," he says. "There is virtually no wildlife damage anywhere near Fukushima. Levels [of radiation] are much too low. Nobody was killed, nobody was even hurt, so what was all the fuss about? It's all propaganda. People badmouth nuclear so nobody dares use it."

He also supports fracking, but only as a second-best to nuclear power. "The government is too frightened to use nuclear, renewables won't work because we don't have enough sun, and we can't go on burning coal because it produces so much CO 2 , so that leaves fracking. It produces only a fraction of the amount of CO 2 that coal does, and will make Britain secure in energy for quite a few years. We don't have much choice."

Lovelock is usually considered to be an opponent of wind power, but he says that's not quite true. He doesn't object in principle, but thinks wind turbines are an inefficient way to produce energy, and doesn't believe the results justify the despoilation of his beloved English countryside. Solar energy? Terrific, he says – in the desert. "Europe could get all its energy from the Sahara, but politics screws it. A solar farm 100 miles by 100 miles could supply energy for the whole of Europe, but terrorists would blow it up." Turning all the lights in Europe off, he points out, would be an even bigger coup for al-Qaida than knocking down the Twin Towers.

Lovelock manages to be both catastrophist and boundless optimist at the same time. He believes humanity will suffer crises that threaten the species, but will somehow pull through. "We shouldn't worry too much about terrible disasters because they've happened in the past [when we may have been down to just a few thousand individuals] and we've come back. We are an extraordinarily special species, the first to harvest information." So we will survive – at least until evolution turns us into something else a few million years down the road? "Oh sure," he says, the afternoon sun bathing his still surprisingly youthful face in light. "As a species, we're cunning bastards."

• An exhibition, Unlocking Lovelock: Scientist, Inventor, Maverick, opens at the Science Museum on 9 April.