It was a perfect moment in cultural history. Well, nearly perfect. Some time in the mid-1960s, James Lovelock, a scientist of international distinction, and his friend William Golding, destined to win the Nobel prize for literature, were taking a walk near the Wiltshire village of Bowerchalke, to which they had both retreated to escape the conventions of gainful employment. Lovelock expounded his almost mystical idea that the Earth and all the plants and animals that inhabit it are a massive, self-regulating entity. Life and Earth are one. All that Lovelock lacked was a name for his hypothesis. Golding, master of literature, had the answer: Gaia, mythological goddess of the Earth.

The problem was that Lovelock thought Golding was suggesting "gyre", a sort of giant whirlpool in the ocean. "They're not self regulating," he laughs. "We walked on for 20 minutes talking at complete cross purposes."

If it had ended up as the Gyre hypothesis, Lovelock may have suffered less flak from evolutionary and mathematical biologists as eminent as Richard Dawkins, Stephen Jay Gould and John Maynard Smith. They all sniped at the new-ageist notion of a self-regulating living Earth in which the evolution of all species is coupled through their shared environment. Lovelock protests that Gaia, the goddess, is just a metaphor. The name has stuck. And he says, most opponents "in private" now admit he's right.

It's paradoxical that Lovelock, the futurist, lives more like an 18th-century scientist, pottering in a barn that doubles as his lab. He was born in Letchworth in 1919, son of Nell, who worked in a pickle factory, and Tom, who had done six months' hard labour for poaching. They moved to London and James had to take a job at a photography company to help support his ageing parents. "I learned more science there than I did at university," says Lovelock. "The most important thing they taught me is never, ever to cheat." The owner recognised his talents and paid for him to attend evening classes at Birkbeck College, and he won a place to study chemistry at Manchester, worked for a while on a Quaker farm, and then, in 1941, went to the Medical Research Council's National Institute in Hampstead as a research student.

He "wandered around the institute" asking people for problems to solve – "a wonderful way of getting around," he says. "As soon as they hear you can invent something they come with their problems – a great way of making friends." He tells the story of making a device to measure mercury vapour and discovering that a pressure chamber designed to study the physiological reactions of divers was so saturated with mercury it would have killed anyone who used it.

Early in the second world war he registered as a conscientious objector. His views changed as news of Nazi atrocities emerged, but when he tried to enlist he was turned down because his research on ways of shielding soldiers from burns was considered more important.

In 1961, after 20 years at the National Institute, just as he was beginning to feel that his work was "dotting Is and crossing Ts", Lovelock got a letter from Nasa inviting him to join the team working on the Viking programme, which hoped to detect life on Mars. Lovelock's job was to design sensors to measure the composition of the planet's atmosphere and soil.

He recalls a pivotal event in 1965, in the Jet Propulsion Laboratory in Pasadena, California. He was writing a paper with the astronomer Carl Sagan when a colleague burst in with news that French scientists, using equipment on Earth, had found that Mars is wrapped in a cloak of carbon dioxide. Lovelock immediately saw that this said more about the Earth than about Mars: our atmosphere is far from an inert equilibrium. It has changed dramatically through the 4.5bn years of its existence, and some of that change was undoubtedly caused by living things. His advice that the Viking probe was "a waste of time" fell on deaf ears. The mission went on, and two of Lovelock's instruments are still up there on the surface of Mars. "I can look in the sky when Mars is visible and get a bit of pleasure from it," he says.

After his return to Britain and self-exile to Wiltshire, he invented a device capable of detecting tiny concentrations of substances in the atmosphere, including the CFCs then used as refrigerants and aerosol propellants. A grant application to support the research failed but, in 1972, the Natural Environment Research Council offered him free passage on their research ship, the Shackleton. His measurements, compared with data from the manufacturer DuPont, produced the scary conclusion that most of the CFCs ever manufactured were still up there in the atmosphere. That was the start of the realisation that the ozone layer was being destroyed by our fridges and deodorants. It was a piece of practical environmental science that set standards for international co-operation and global action.

It's hard to avoid the impression that Lovelock relishes his maverick image. He has been at the forefront of dire predictions about the consequences of global warming. "Before this century is over billions of us will die and the few breeding pairs of people that survive will be in the Arctic where the climate is tolerable," he wrote in 2006.

Yet he is vilified by the green movement for his enthusiasm for nuclear power. "The public perception of the danger of the nuclear is that it's possibly the greatest danger there is," he responds. "But the greatest danger is climate change itself."

He is withering in his criticism of the "scam" of commercial exploitation of renewable technology – "to produce solar voltaic energy in Britain does nothing except benefit German industry" – and is still seen as an outsider by the stuffier cliques of academe. Yet, despite his gloomy prognostications – "I think we expect too much of our scientists," he warns – he still bubbles with excitement at the possibility that cataclysmic disaster might be prevented by ocean pumps, or nanoparticles injected into the high atmosphere. Ever the inventor.

• You can read all about the Observer Ethical Awards in a special edition of the Observer magazine this Sunday

Observer Ethical Awards full winners list

Local retailer: The People's Supermarket

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Campaigner sponsored by B&Q: Compassion in World Farming

Global campaigner: Greg Valerio

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Conservation: Thameside Nature Park

Blog: Shirahime

The Observer lifetime achievement award: James Lovelock