‘IT’S IMPORTANT for Gaia that human beings survive,” says James Lovelock .

“Our intelligence, if it can be integrated as part of the whole planetary system, would make ours the first intelligent planet in the galaxy, perhaps. What a wonderful future for humans!”

A great scientist needs great courage and a great imagination — and Jim Lovelock has both, in spades.

It is now 40 years since he rattled the scientific world and electrified the rest of us by publishing Gaia: A New Look at Life on Earth (1979), which argued that the Earth behaves like a single living organism that creates and maintains a viable environment for life.

The Gaia hypothesis — named for the Greek Earth goddess — implied that the world was far more complex than modern reductionist science had imagined. It offered a coherent vision of the whole living world that echoed all our wisdom traditions and renewed the human sense of wonder.

Mainstream scientists were horrified. Many still are. But Lovelock’s bold insights, and his continuing exploration of their implications, became the foundations of “Earth system science,” the study of systems like the circulation of the oceans, the maintenance of the atmosphere and the relationships among the earth’s many systems.

Noted author Gwynne Dyer considers Lovelock “the most important figure in both the life sciences and the climate sciences for the past half-century,” and compares his achievements to Darwin’s.

Slight, cheerful and white-haired, Lovelock is now 90 years old, though he looks decades younger. He published a new book last year, The Vanishing Face of Gaia. He and his American-born wife Sandy spend their summers in Devon, England, and their winters in her home town of St. Louis, Mo., where I came calling one brilliant January morning.

Lovelock resembles a geologist in his easy navigation of the vastness of deep time, but he recalls the Enlightenment sages in his assumption that science is a single enterprise, artificially split into disciplines. He has been self-employed as a freelance scientist and instrument-​​​maker for 50 years, largely because of “silly people who would say to me, ‘You can’t do biology, you’re a chemist.​​’ As if I didn’t have a brain.”

Freedom from institutional politics allowed him to indulge his preference for observation over computer modelling and permitted him to follow the evidence fearlessly, wherever it led.

In 2007 he was “shocked” to learn that the Intergovernment​al Panel on Climate Change had “reached a consensus on a matter of science.”

Science is about nature. Consensus is about politics.

So where has the evidence led him lately?

Sea level, Arctic ice cover and ocean algae populations, he says, are the best indicators of global warming — and they all reveal that the earth is heating up much faster than the panel’s projections. Furthermore, the evidence from the Earth’s last hot period, 55 million years ago, shows that global temperatures don’t necessarily change slowly and evenly; they can flip fairly quickly to hotter or colder states.

On that earlier occasion, most of the Earth became a scorching desert. Life retreated to the shores of an Arctic Ocean with surface temperature of 21 C, where crocodiles lived and bred.

Lovelock thinks that’s the kind of world we’re creating — and because of our essentially tribal politics, our efforts to avoid it will likely fail. Since a less habitable Earth won’t sustain a global population of seven billion, populations will crash. Human beings should plan a “sustainable retreat” to the Arctic region. Canadians should prepare for hordes of people trying to relocate to northern Canada.

Is this inevitable?

No, says Lovelock. Gaia is far more complex than we understand, and we do not even know the depth of our ignorance. A scientist can only say that this nightmare scenario is probable. But we should prepare for it now, while the world is still a reasonably civilized place.

The real horror would be if our species survived, but its finest achievements were lost — science, art, culture.

Lovelock believes we could be the evolutionary ancestors of an intelligent, post-tribal species that will serve an aging Gaia as her consciousness.

This is a colossal vision of tragedy — and redemption.

Lovelock smiles.

“Gaia needs us,” he says. “What a wonderful future for humans!”