James Lovelock, the scientist and writer, is 100 years old on Friday and remains a combination of environmental Cassandra and Old Testament prophet. Unlike them, though, he changes his mind about what the future holds. Foolish consistency, Emerson wrote, is the hobgoblin of little minds, and Dr Lovelock’s mind is not little. More than 10 years before the record high July temperatures, Dr Lovelock flatly told the Guardian that 80% of human life on Earth would perish by 2100 because of the climate emergency. He imagined a dystopian end of humanity where “the few breeding pairs of people that survive will be in the Arctic where the climate remains tolerable” by the end of the 21st century.

As a scientist (his first letter to Nature was published in 1945, on the subject of writing on petri dishes), Dr Lovelock’s life has been studded with insight. He invented an electron capture detector that could pick up minute traces of pollutants – such as the pesticides that spurred Rachel Carson to write the 1962 book Silent Spring. At home he built instruments that ended up on Mars, helping Nasa to establish that the red planet was lifeless.

Dr Lovelock’s imagination has not narrowed, but his vision has become bleaker with time. His new book Novacene: The Coming Age of Hyperintelligence proposes that the 300,000-year Anthropocene era of Earth’s human domination is ending. Novacene is a new age where our species is doomed to a worse fate than clinging on for dear life at the north pole as previously imagined. Instead we will become lackeys of cyborgs able to think 10,000 times faster than humans. We will be kept on to ensure there are habitable temperatures for these superior intelligences.

Novacene’s thesis is a straight-line extrapolation of Dr Lovelock’s breakthrough idea which he began to develop while a consultant at Nasa in the 1970s; the thought that the planet was a superorganism. In 1974, he and biologist Lynn Margulis proposed the Gaia hypothesis, which holds that Earth is in some way alive. The paper suggested our planet metabolises and responds to changes in its environment to survive. In bestselling books such as The Revenge of Gaia, Dr Lovelock argued that humans have exploited Earth and the “old lady” would eliminate us unless we treated her with greater reverence. That is why the Novacene will start, he now reasons: because a superintelligence will recognise that all living tissue will be consumed by climate crisis and will act with Gaia to keep the life going.

When it came out, the Gaia theory immediately chimed with the incipient green movement. Tough-minded scientists, though, initially reacted as if – as one critic put it – Dr Lovelock had let off a bad smell at the vicar’s tea party. Its appeal, they wrongly sneered, was to devotees of faith-healing and mysticism.

But Dr Lovelock has stuck to his guns and refused to be co-opted by environmentalism. He backs nuclear power and has zigzagged on global heating, saying that some alarmist books – including his own – had made unwarranted predictions. He even told the Guardian: “We’ve got to really make it clear to those very silly people who think we can save the planet to cease and desist.” And what of the Gaia hypothesis? Evolutionary biologist Stephen Jay Gould described it as “a metaphor not a mechanism”. Its truth is poetic not literal. That echoes how Dr Lovelock sees himself. “I’m a romantic,” he said once. “I’m much more of a poet by nature than anything else.”

He might be best seen then as a 21st-century William Blake – one whose words are no more testable than verse, but no less valuable for that.