Australian climate scientist Andy Pitman only met James Lovelock once at a conference and remembers a "classic elderly, charming Englishman", but it's an image that belies nothing short of a revolutionary influence.
For someone like Professor Pitman, who studies the interaction of climate and vegetation, it's obvious that living things play a key role in regulating Earth's climate.
"If it wasn't for life, we would have cooked long ago, because life sucks the carbon dioxide out of the atmosphere into the land," says Professor Pitman, of the University of New South Wales.
But when Professor Lovelock first went public with his idea that the Earth was a giant organism that could regulate itself (including its climate) by using feedback between biological life and the rest of the planet, it was seen as rather radical.
"It was just so out there. It wasn't taken very seriously by many," Professor Pitman says.
But that was back in the 1970s — and today, even though many of Professor Lovelock's ideas remain controversial, his Gaia theory underpins a whole field of research called Earth systems science.
"I cannot overstate how profoundly transformative his contribution was," Professor Pitman says
"There are many people who think he has had more impact on our understanding of the Earth than any other singular scientist through the 20th century."
Life on Mars
Professor Lovelock, who died last week on his 103rd birthday, has been described as the "ultimate polymath" and a "connoisseur of nature" for whom "intuition and feeling" were just as important as science and data.
"My role has been to bring separated things and ideas together and make the whole more than the sum of the parts," he once told The Guardian.
It all started back in the 1960s when Professor Lovelock, while working for NASA, designed an instrument to measure the chemical composition of Mars's atmosphere.
After comparing his measurements with those taken from Earth's atmosphere, he concluded there could be no life on the Red Planet.
Professor Lovelock argued the Martian atmosphere did not contain the signature balance of gases including oxygen, which is a sign of life on our planet.
"He basically was able to demonstrate without sending robots to Mars that there was no life there," Professor Pitman says.
The findings changed the way we understand Earth's atmosphere and its relationship to the rest of the planet.
In 1987, Professor Lovelock and colleagues proposed that phytoplankton in the ocean helps regulate the climate by giving off a gas, especially when it is sunny, which helps form clouds that shade the Earth, and bring rain that helps forests grow.
While scientists still debate how these cycles work, it was complex planet-scale interactions like this — involving biology as well as physics and chemistry, and the recycling of nutrients — that were key to Professor Lovelock's thinking.
Professor Pitman likens the feedback processes central to Gaia theory to what happens in our bodies to regulate temperature — we sweat when we're hot and shiver when we're cold.
He says Professor Lovelock's writings were "essential reading" for his own PhD back in the 1980s, and a vast amount of what we understand today is the result and direct consequence of such work.
Like minds with a planetary perspective
The idea of using the name Gaia — the Greek goddess who personifies the Earth — originally came from a chat with novelist William Golding of Lord of the Flies fame. And a Pentagon consultant by the name of Dian Hitchcock also appears on an early scientific paper of Professor Lovelock's.
But his key long-term intellectual collaborator was the evolutionary theorist, microbiologist and fellow maverick Lynn Margulis, who overturned our understanding of how life on Earth evolved.
Professor Margulis also had a planetary perspective on things, says Bruce Clarke, of the Texas Tech University, who is a co-author of Writing Gaia, a new book that analyses 300 letters exchanged between professors Margulis and Lovelock between 1970 and 2007.
"She understood life as a global or planetary phenomenon," Professor Clarke says.
That's not surprising given that Professor Margulis was once married to cosmologist Carl Sagan, who knew Professor Lovelock, and suggested his wife connect with him.
"Lynn believed Gaia is run by the microbes," Professor Clarke says.
As well as collaborating on ideas, professors Lovelock and Margulis (who died in 2011) supported each other, in justifying their opposition to mainstream ideas, he adds.
And during the '70s and '80s it was them against scientists like Richard Dawkins, who was reducing life to a "molecular gene-centred vision" that made living organisms all "lumbering gene robots" at the mercy of their environment.
"For the longest time, Richard Dawkins was their mutual nemesis."
Gaia myths and climate prophecies
The fact that Gaia had mystical or spiritual connotations that resonated with many in the New-Age movement undermined Professor Lovelock's ideas in the eyes of some scientists.
So he spent a lot of time explaining that Gaia was not some kind of benevolent Earth mother, but it would take care of itself first, even if that wasn't great for humans.
As his collaborator Professor Margulis said: "Gaia is a tough bitch."
Professor Lovelock is also well known for warning of the dire consequences of human activity pushing Gaia to the limit.
At the age of 86 he published a book called The Revenge of Gaia, which predicted destructive extreme weather from climate change would be the norm by 2020.
He even thought the COVID pandemic might be "a Gaian negative feedback mechanism to reduce human pressure on the Earth system".
At the same time, he argued humans were part of Gaia, and needed to use their consciousness to "give her a hand" to stave off the worst of climate change.
Professor Lovelock shocked many environmentalist fans, for example, by advocating the use of nuclear energy and then geoengineering as solutions to global warming.
His recipe for human salvation also included human retreat to megacities and artificial intelligence controlling the climate.
A free thinker
Whatever you think of James Lovelock, he will be remembered for being a truly independent scientist, which, Professor Pitman says, is "a very rare" thing in this day and age.
"He was a free thinker who thought outside the box … and had hard core scientific credentials."
Professor Lovelock was elected a Fellow of the Royal Society not long after his first paper on Gaia was published, and has received many other honours.
And it seems he was able to be so independent because he funded his own work, with the help of the income from no less than 40 patents from inventions he had created over the decades.
These included the electron capture detector, which ended up detecting ozone-depleting chemicals.
Professor Lovelock's protégé, Tim Lenton, a professor of climate change and Earth systems science at the University of Exeter, believes his mentor's ideas on the interconnectedness of Earth's systems will help humans build a more sustainable future.
"He will go down in history as the person who changed our view of our place on Earth," Professor Lenton says.
"We need Jim's way of thinking now more than ever, if we are to get out of a climate and ecological crisis of our own making."
