A resolute independence has shaped James Lovelock’s life as a scientist. On the occasions over the past decade or so when I visited him at his home in a remote and wooded part of Devon to discuss his work and share our thoughts, I found him equipped with a mass of books and papers and a small outhouse where he was able to perform experiments and devise the inventions that have supported him through much of his long career. That is all he needed to carry on his work as an independent scientist. Small but sturdily built, often laughing, animated and highly sociable, he is, at the age of 93, far from being any kind of recluse. But he has always resisted every kind of groupthink, and followed his own line of inquiry.

At certain points in his life Lovelock worked in large organisations. In 1941, he took up a post as a junior scientist at the National In - stitute for Medical Research, an offshoot of the Medical Research Council, and in 1961 he was invited to America to join a group of scientists interested in exploring the moon who were based at the National Aeronautics and Space Administration (Nasa). It was during his time at Nasa that Lovelock had the first inklings of what would become the Gaia theory – according to which the earth is a planet that behaves like a living being, controlling its surface and atmosphere to keep the environment hospitable to life. He has since worked closely with other scientists, including his former doctoral student Andrew Watson, who is now a professor of environmental science, and the late American microbiologist Lynn Margulis, in developing the theory.

Lovelock has always cherished the freedom to follow his own ideas and stood aside from institutions in which science is conducted as a vast collective enterprise. Partly this is an expression of his ingrained individualism, but it also reflects his radically empiricist view of science as a direct engagement with the world and his abiding mistrust of consensual thinking. In these and other respects, he has more in common with thinkers such as Darwin and Einstein, who were able to transform our view of the world because they did not work under any kind of external direction, than he does with most of the scientists who are at work today.

Lovelock was born in 1919 in Letchworth, Hertfordshire. His parents were working class –his mother had left school at the age of 13 to work in a pickle factory – and because he could not afford to attend university he took a job as a laboratory assistant after leaving school. Most of the science he learned as a boy came from the books he borrowed from the public library in Brixton, where his parents ran a small business. Far from viewing this as a privation, Lovelock believes it helped him to become a generalist who could move freely between the proliferating disciplines, increasingly narrowly defined, into which science has been divided. If he had received a specialised scientific education he might never have developed the Gaia theory at all.

As Lovelock explains in Homage to Gaia: the Life of an Independent Scientist (2000), the idea of Gaia came to him when he shared the view of the earth from space of the Apollo astronauts: “Suddenly, as a revelation, I saw the earth as a living planet.” Much later, when already nearly 90 years old, he eagerly accepted Richard Branson’s gift of a trip into space on the Virgin Galactic shuttle when it makes its inaugural flight. He wanted, he told me, to see the face of Gaia.

There can be no doubt that the idea of Gaia came to Lovelock as a kind of epiphany. But the Gaia theory originated in the experimental difficulties of detecting signs of life on Mars, and he has developed the theory in rigorously scientific terms, producing a computer model of a virtual planet (Daisyworld) in which a self-regulating climate could emerge from simple organisms by a process of natural selection. The novelist William Golding was a neighbour of Lovelock’s in the Wiltshire village of Bowerchalke and became a close friend. He proposed the name of Gaia – the earth goddess in Greek mythology – for the self-regulating planet. Although Lovelock is grateful to Golding for his inspired suggestion, he views the notion of the earth as a self-regulating system as an integral part of science.

This insistence that Gaia is science, rather than myth or mysticism, has distanced Lovelock from greens for whom environmentalism has become a religion. An agnostic, he recognises the need for transcendence. As he put it to me in a recent email exchange, “It has always seemed that many would have faith in Gaia . . . I prefer to keep a trust in Gaia; it is more consistent with science.”

Turning to Gaia for a God-substitute, as some greens have done, seems a fundamental error. Though vastly older and stronger than the human species, Gaia is neither omnipotent nor immortal – and, unlike the God of western monotheism, it has no particular interest in human beings. The goal of a selfregulating system is to renew itself, rather than preserve any of its constituent parts, and if human beings become an obstacle to that end they will find Planet Earth increasingly inhospitable.

As a view of the world, the Gaia theory is thoroughly ecocentric, and this is another feature of Lovelock’s ideas that has put him at odds with recent green thinking. “I am old-fashioned green,” he told me, “a follower of [Aldo] Leopold, Blake and of the naturalist instincts of Rachel Carson, those where she was concerned about the effects of pesticides on wildlife, especially birds.”

In the Gaia theory human beings aren’t at the centre of things. To be sure, humans are having a big influence on the planet. Through carbon emissions and by destroying the biosphere, we are altering the planet irreversibly. That doesn’t mean we can control the change in climate our activities have set in motion. The earth system will respond so as to restore some kind of balance, regardless of human plans. Finally dislodging the human animal from primacy in the world, the Gaia theory can be seen as completing Darwin’s work.

In rejecting anthropocentrism this way, Lovelock finds value in the larger system in which human beings belong, with other animal species. During his time as a medical researcher, he was required to measure the heat that causes burns by burning the exposed skin of live rabbits. Even though they weren’t anti-vivisectionists, he and a colleague refused to do so, and performed the test on their own skin instead. To begin, he found the effect “exquisitely painful”, but after a time it faded away and he was able to perform the experiments on himself without difficulty.

As this story shows, other living things are not, for Lovelock, simply resources to be exploited by humans; but he rejects firmly any Romantic belief in the intrinsic benignity of the natural world of the kind that is often found among urban greens. As he put it to me, “Modern greens are mainly concerned about people living in cities and the effects of changes in the environment on humans. Because they are city-dwellers and only rarely see or walk in the natural world, many of them have a confused idea of what is natural. I have the feeling that urban greens would rather eat deadly nightshade in their salads than GM lettuce.” In his book Eco-socialism: From Deep Ecology to Social Justice (1993), the left-environmentalist David Pepper berated Lovelock for his “distaste for seething urban humanity”. However, the real difference between Lovelock and conventional greens of all political stripes is his consistent rejection of any view in which the chief role of the earth and its diverse life forms is to serve human wants and ambitions.

This rejection of anthropocentrism helps explain another manner in which he differs from contemporary greens. One of the reasons why Lovelock has long supported nuclear power is that its impact on the environment has been vastly less malignant, even in cases of disaster such as Chernobyl and Fukushima, than industrial technologies such as coal mining. His view of nuclear power is one that I share – along with Mark Lynas and George Monbiot, among others – but it is anathema to most greens. More recently he has come out in support of fracking, not as a solution to our energy problems but as a way of buying time. Lovelock favours these technologies on pragmatic grounds, but there are deeper reasons why his view of them is at odds with that of most contemporary greens.

While it would be an exaggeration to represent most of those active in green movements as neo-Luddites, greens are generally scornful of technical fixes. If they favour new technology, they do so as part of a drastic change in society, which to many of them implies rolling back globalisation and relocalising economic life. What they have in mind, in effect, is a post-industrial economy powered by low-tech means – windfarms, solar energy and the like – and fed by organic farming. Rightly, to my mind, Lovelock is sceptical of all such schemes. The great majority of human beings want the style of life that advanced countries enjoy, and they will not be persuaded otherwise by sermonising.

In any case a low-tech, relocalised economy would not deal what Lovelock regards as the fundamental problem: the rising numbers of human beings. Climate change has not always been caused by us; there appear to have been several large shifts before the human species existed. However, if the current global warming is anthropogenic (as Lovelock still firmly believes), human numbers play a critical role in the process.

When I suggested to him that the perennially unfashionable Thomas Malthus may in the long run be shown to have been on the right track, he responded: “Yes, John, I agree strongly with you that rising population is probably the greatest danger. If we had stayed at Malthus’s numbers, one billion, there would be no climate problem.”

Like nearly all economists, most greens insist that Malthus was wrong. The problem, they say, lies in the resource intensity of the western way of life; what we need to counter this is a global redistribution of power and wealth. I am not sure if Lovelock shares my view that this is an entirely utopian prospect, but he is clear that sustainable development – the current mantra – cannot deal with the challenges posed by a rising population. What is needed instead, he suggests, is sustainable retreat: a strategy of reducing the human impact on the planet by abandoning old modes of food production and embracing high-density urban living. (There are parallels between Lovelock’s ideas on these issues and those of Stewart Brand, the editor of the Whole Earth Catalog.)

Almost certainly, a world population of ten billion or more – the level that experts estimate we will reach some time later this century – cannot be maintained indefinitely.

And yet, by using the technologies most demonised by contemporary greens – genetically modified food, fracking and nuclear power, for instance –humankind could make possible a decent standard of living until our numbers fall globally (as they are doing already in some parts of the world) and eventually stabilise at a lower level.

The realistic alternative is a succession of intensifying resource wars in which endangered human groups fight for control of oil, water, minerals and arable land: “a global decline into a chaotic world ruled by brutal warlords on a devastated earth”, as Lovelock described the darker human prospect in The Revenge of Gaia (2006).

He remains open to the possibilities of geo-engineering, deliberately changing the oceans, air or land surface of the planet with the aim of countering global warming, but questions whether we understand the climate well enough to manage the large risks that geo-engineering involves. “We are not clever enough to handle either the earth or ourselves,” he says. The way forward is to use human inventiveness to adapt to a shift in the environment that can no longer be prevented, and leave recovery to the resilience of Gaia. For the foreseeable future, human beings will most likely muddle through.

In some earlier statements he envisioned a future in which the species might be reduced to small numbers of hunter-gatherers eking out a meagre existence in the Arctic. Such projections were meant to serve as wake-up calls rather than forecasts, but Lovelock concedes that they do illustrate the dangers of “relying too much on model predictions”. He is now more concerned to stress the inherent difficulty of predicting the precise course of climate change. Not for a moment has he become a “sceptical environmentalist”; the scientific evidence points unmistakably in the direction of anthropogenic climate change. He remains what he has always been – a thoroughgoing empiricist, ready to temper his views as the world and our understanding of it changes.

Lovelock has sometimes been portrayed as a prophet of doom. That picture has nothing in common with the man I have known for many years. Cheerful, humorous and life-affirming, he is a passionate talker – and an equally passionate walker. Last summer he moved with his wife, Sandy, to a coastguard’s cottage in Dorset and he told me that the achievement of which he is most proud is walking the 630-mile South West Coast Path with her in 1999. His strong individualism goes with no less strong a sense of the need for community. Registered as a conscientious objector during the Second World War, he applied in 1944 for his exemption from military service to be cancelled. “I had not the heart to stand by nursing my convictions,” he writes in Homage to Gaia, “while the rest of the community, not least the brave merchant sailors, brought in the food that saved me.” A spell of illness many years later, during which he spent periods in hospital, led him to cherish the National Health Service, he told me once, as a unifying social institution. His love of life goes with a natural friendliness towards other human beings.

Where he differs from many is that his life affirmation is not restricted to human beings. He tells me his next book will consider the possibility that evolution may produce another species, one more capable than human beings have been of coexisting with other life forms on the planet. His intellectual iconoclasm showing no signs of diminishing, Lovelock, in his tenth decade, continues to produce ideas that fundamentally challenge the prevailing world-view. A unique thinker, he has no obvious successor, yet in gaining wide acceptance of the idea that our planet is a self-regulating system, he has had a profound effect on many branches of scientific inquiry. Along with millions of others, I can’t wait to hear the latest thoughts of the scientist who, more than any other alive today, has changed the way we think of the earth and our place on it.

John Gray’s most recent book, “The Silence of Animals”, is published by Allen Lane