The Lantau experiment, a joint project with the Swire Institute for Marine Science at the University of Hong Kong, is part of the painstaking detective work that is taking Nisbet and his team across the world – from the Arctic to Amazonia, and, of course, Hong Kong. And the results of their studies will have implications for the future of life as we know it.

Methane is the simplest of the many organic chemicals, known as hydrocarbons, which predominate in fossil fuels. If you cook using natural gas, most of the blue flame is the result of methane burning, reacting with oxygen to form carbon dioxide (CO₂) and water.

Methane is one of the four main greenhouse gases. Along with CO₂, water vapour and nitrous oxide, it causes the Earth’s atmosphere to retain solar energy that would other­wise escape into space. Molecule for molecule, it absorbs more infrared radiation than CO₂, making it a more potent greenhouse gas.

It’s relatively easy to estimate the magnitude of methane’s role as a greenhouse gas: simply measure how much infrared it absorbs in a laboratory and combine the result with a figure representing the amount of methane in the atmos­phere. Getting a detailed picture, however, is far more difficult, partly because atmospheric methane is oxidised through chemical reactions, meaning most of the gas released will be gone within nine years. Furthermore, the amounts released into the atmosphere are in constant flux, as they come from a complex mix of sources, including industry, natural gas exploration, rotting vegetation, rice fields and – you guessed it – belching cows and water buffalo.

Rising methane levels have been responsible for perhaps a fifth of the additional warming by greenhouse gases the world has experienced since pre-industrial times. Writing in Science magazine, Nisbet and his two co-authors note that the growth rate of atmospheric methane slowed in the late 1990s, and the total amount was nearly constant between 1999 and 2006. But significant growth resumed in 2007 – and no one knows why.

It’s the search for an answer that brings Nisbet to Hong Kong.

Given that his early career was focus­ed on ancient volcanic rocks, Nisbet might seem an unlikely candi­date to lead a squad of global “gas­busters”. Yet his ancestry, background and inquiring mind make him uniquely suited to the role.

“I was born in the ruins of Germany and grew up in South Africa and Zimbabwe,” he says. “I went to univer­sity in Zimbabwe, for six months, and did badly.”

Luckily for Nisbet, a wealthy donor had left funds to cover the education costs of people in Zimbabwe, and he gained a scholarship to study at Britain’s Cambridge University. He initially read physics but his interests changed.

“My great-grandfather, Andrew Geddes Bain, was the first geologist in Africa. I’ve got a bushman painting of him,” says Nisbet. “I got more and more interested in geology and shifted to it in my final year.”

It was during a professorship at the University of Saskatchewan, in central Canada, that he roamed the Arctic tundra and encountered what he realised may have been symptoms of climate change.

“I saw bubbles coming up and wondered, ‘What are the bubbles doing?’” he says. The bubbles contained methane from decomposing vegetation and Nisbet realised he could study the phenomenon using isotopes – variants of an element that differ only in their atomic weight – much in the way he had studied early life forms known as stromatolites, and shed light on Earth’s environment almost three billion years ago.

Looking at methane in this way would mean studying the Earth as it is today, and gaining insight into what it might be like in the not-too-distant future.

Nisbet shifted from pure geology to environmental issues. In this, too, he was influ­enced by his background.

“My family were foresters and environmentalists in South Africa,” he says . “One of my great-grandfathers was the chief conservator of forests for South Africa, before the first world war. Another great-grandfather founded the botanical garden in Cape Town. My father was a Southern African Presbyterian and was concerned about our guardianship of the environment.”

Nisbet says he grew more and more worried about what was happening to the planet.

“I became aware of climate change in the 1980s, when I saw ice core data [from Antarctica and Greenland]. It was clear greenhouse gases and temperature are closely linked.”

To Nisbet, author of the 1991 book Leaving Eden, our response to the challenge is “fundamentally down to human choices; whether we see ourselves as guardians or exploiters of the environment. Even economics should be about stew­ard­ship, but we sometimes tend to forget this, and focus on making money”.

Nisbet’s budgets involve carbon rather than dollars.
“The Venusians have lost all their carbon to the atmos­phere,” he says.

Not that there are any sentient beings on Venus, of course, and even if there were, a surface temperature of 500 degrees Celsius – thanks to global warming so extreme the planet’s oceans evaporated – would soon send them packing. On Earth, by contrast, most carbon has been precipitated out in the form of limestone and coal, leaving CO₂ and a little methane – and temper­atures that can sustain life.

“The system runs rather well,” he says.

With humans adding to green­house gases, however, the system is under increasing strain, and global temper­atures are rising.

There has been extensive research into CO₂, partly because so much of it is generated but also because it’s relatively stable in the atmosphere – add some today and some of it will still be there in thousands of years. Also, CO₂ is believed to be a key driver of temperature change.

As he began studying methane, Nisbet realised that enormous amounts of the gas are locked in a form of ice known as methane hydrate, or clathrate, which is abundant beneath the Arctic permafrost and ocean depths. He wrote a paper suggesting a massive release of methane from hydrate could have played a role in ending the last ice age – resulting in an intensification of warming that spurred more changes, leading to our current interglacial period.

Others then began worrying that we, too, might be threat­ened by a sudden methane hydrate release causing abrupt climate change. A term was coined for this cata­strophic peril: “clathrate gun”.

Happily, Nisbet believes there is no imminent danger from methane hydrate. One of his team members, Rebecca Fisher, has analysed the methane emerging from deep-sea sources and found that it does not reach the atmosphere. And although methane was a culprit in the Deepwater Horizon oil rig blowout in the Gulf of Mexico, in 2010, most was similarly oxidised before it could get to the surface.

Nisbet leads the atmospheric methane group at Royal Holloway college, University of London. Much of his work is pains­taking and unglamorous, aside from that paper on dinosaurs he co-authored, which reported: “Our calculations suggest that sauropod dinosaurs could potenti­ally have played a significant role in influencing climate through their methane emissions.”

Even Fox News was captivated, twisting the findings to declare, “Dinosaurs may have farted themselves to extinction, according to a new study from British scientists.”

The Smithsonian magazine duly stepped in with a correction: “A new study claims dinosaur farts contributed to prehistoric climate change, but don’t believe reports that they gassed themselves to death.” Yet it, too, erred in writing of flatulence.

When I mention this to Nisbet, by e-mail, he curtly notes: “Sauropod eructation? – front end!”

And it’s eructation – belching, to you and me – that brings Nisbet and his team to Pui O. Ruminants such as cattle produce methane while digesting plant material. But with most of his data having come from northern areas in the West, Nisbet wants samples from tropical Asia.

AFTER CAPTURING SOME buffalo breath in a bag, the team seal it, assign it a code linked to notes on time, wind speed and other variables, and carefully place it in a reusable shopping bag together with precious samples collected earlier. The bags will be packed in boxes and posted back to the university to determine carbon isotope ratios – which should act like signatures for the buffalo; methane from a biological source has “lighter” isotopes than those found in gas given off by fossil fuels or in a natural leak.

When methane levels rose in the 1980s and ’90s, there was a shift towards the heavier isotopes, neatly dovetailing with notions that the key sources were natural gas and the burning of fossil fuels. But the current rise is different.

“There’s a shift to significantly lighter methane, including when levels went up dramatically in 2014,” Nisbet says. What’s been driving the increase? It’s clearly a biogenic source, and as growth tends to be tropical and in the south­­ern hemi­sphere, it’s probably cows or rice fields, or tropical wetlands.”

Nisbet suspects South American wetlands bear most of the blame, but he also needs to assess data from Asia. As well as Hong Kong’s buffalo and cattle, the team are inspect­ing rice-farming areas in Yi O, on Lantau, and Hok Tau, north of Tai Po.

“Mad dogs and Englishmen,” Nisbet announces, in Yi O, quoting from the Noel Coward song on the foibles of going out in the midday sun. It is indeed scorching – more than 35 degrees in the shade, according to the team thermometer, but today Nisbet likes it hot, because that helps with the capture of methane.

“Bubbles!” he says, as he scrutinises one of the paddies. He deploys the pole and hose while Brownlow pumps air into a bag.

“Sample number two is ‘Drainage ditch below rice fields’; and I see bubbles in it,” says Nisbet. “I’m desperate to get something with methane.”

Sample bags are filled with air from just above the water, and then again two metres higher, and from nearby man­groves. Reusable shopping bags are filled with sample bags and Fisher takes meticulous notes.

The team have a car equipped for methane sampling. Under a strange-looking roof rack, in the back of the vehicle, there’s a hefty piece of equipment that “sniffs” incoming air and sends a real-time readout of its components to a laptop. At Hok Tau, Fisher shows me an image sent by the equip­ment: a red line marks their route on a Google map, and there’s a great spike in methane that appeared as they passed a public toilet block, where a truck was pumping out the septic tanks. Nisbet seems delighted to have captured a record of our stinking poop.

Dubbed “marsh gas” for its close association with decom­posi­tion, methane is also of special interest to Dr James Hansen, former head of the Nasa Goddard Institute for Space Studies, in New York, who has done much to inform the world about global warming.

“Methane will be addressed in the book I am writing now, Sophie’s Planet, which describes the f**king mess that we are leaving for young people,” Hansen informs me by e-mail. “We will need to get a major reduction of atmospheric CH₄ [methane], pushing it back closer to its pre-industrial level. That is possible, but it requires quantitative under­standing of all major methane sources.”

Drew Shindell, professor of climate sciences at the Nicholas School of the Environment, Duke University, in the United States, adds, also via e-mail: “I think we need to simul­taneously clarify to policymakers both WHY and HOW they should reduce methane, via quantifying the many damages resulting from emissions and documenting where they’re coming from and what technologies and policies could reduce them. Nisbet’s work is an important part of the latter, along with satellite data, etc.”

WHEN NISBET WROTE Leaving Eden more than 25 years ago, climate change due to human activity was largely a theory. But its fingerprint has become increasingly evident. Indeed, Nisbet’s team was in Hong Kong during a record-breaking warm spell, when daily temperatures soared above 35 degrees on four consecutive days, during the world’s hottest June on record – the 14th month in a row to break previous records.

Shortly after returning to London, Nisbet sends me a new paper by American researchers who have found that the world’s clouds are shifting towards the poles and reaching higher into the atmosphere, a development that could exacer­bate global warming.

A solution would be to stop using fossil fuels, of course, but “without oil, for 90 per cent of the world, there would be no ploughing, no food transport. If we stopped tomorrow, it would kill five to six billion people; the carrying capacity without fossil fuels is at most one billion.

“We’re hooked on ‘heroin’, how can we come off it?” asks Nisbet, who favours an end to oil exploration and the running down of major sources while alternatives are developed.

Yet too many of the world’s policymakers seem intent on denying or avoiding the issue. Britain has just shut its climate change department; Philippine President Rodrigo Duterte says his country will not honour the commitments it made under the Paris climate change deal; and, in Donald Trump, the US has a presidential candidate who believes “the concept of global warming was created by and for the Chinese”.

In Hong Kong, you only have to walk down a street and feel air-conditioned breezes wafting from wide open door­ways to appreciate the lack of urgency about the issue.

In Leaving Eden, Nisbet warned that a policy of little action now would be followed by “a massive forced change in our civilisation in the early decades of the next century”.

There has indeed been little action, and as greenhouse gas levels rise, we face ongoing climate change – perhaps spurred by methane emissions.

“Standing on [Norwegian archipelago] Svalbard and seeing ice all around, it’s hard to believe it can change – but it will,” Nisbet reflects. “I can see climate conflicts coming.”