"It was one of most spectacular places on the whole reef, and apparently one of the most remarkable sites in the whole world. And now, you may as well go dive on a parking lot some place.”

The reef a kilometre further out, where merely half the corals had died, offered some cheer. "There was still great beauty and a great sense of what an enchanted corner of God’s brain this all was."

McKibben's own wits don't seem to get much downtime, either.

A prolific writer, the lanky Vermonter - when he's not researching or campaigning around the world - was among the first to popularise climate change as a major threat with his 1989 book, The End of Nature. 

His working title for the three-decade anniversary update next year - “Falter: Has the human game begun to play itself out?” - suggests things aren't looking up.

“Thirty years ago, I didn’t anticipate how quickly the world would change, and I didn’t anticipate how slowly the political world would respond," McKibben says. "I was remiss on both counts."

He isn't letting up though. To anyone following his Twitter feed, it's evident McKibben remains passionate about many issues - from lawsuits against oil giants for their climate impact, new worrying science such as confirmation of a slowdown in the Gulf Stream, to US President Donald Trump's latest announcement.

McKibben's journalistic nous was nurtured as an undergraduate at Harvard where he "theoretically" majored in government. In reality, he spent "day after day after day" on The Harvard Crimson, the campus newspaper that doubles as an incubator for future New York Times or Washington Post talent.

"I’m sure I wrote more words per day in my college years than any other part of my journalistic career,” he muses.

McKibben's news nose means he appreciates the difficulties journalists have keeping the climate issue in the public eye.

That's despite the science being basically settled since the first Intergovernmental Panel on Climate Change report in 1994, and the mounting evidence of more frequent and more extreme weather events as atmospheric concentrations of greenhouse gases continue to climb.

“Although [climate change is the] most important thing happening in the world every single day, it’s never the most dramatic, urgent thing on any particular day,” he says.

“It may be journalism is just a reflection of the brain of our species, which is not good at reacting.”

I raise the point that news on the climate science front also tends to be negative, citing the recent discovery of algae forming on the warming Greenland ice sheets, darkening the surface and speeding the melt. 

“We’ve not caught a significant break from physics or chemistry or biology in the 30 years I’ve been working it," he agrees. "Instead, virtually everything’s come back worse than imagined."

Indeed, some processes - such as ocean acidification as the seas absorb more carbon dioxide from the atmosphere - were barely foreseen when The End of Nature first went to print, he says.

For many Americans, the election of the pro-fossil fuel President Trump - who has also sought to gut government climate action - has added a degree of dismay that few liberals saw coming.

"[It's] as if everybody’s taken a dose of reverse Prozac, and they’re just anxious and jittery at all time,” McKibben says.

“It turns out to be an under-appreciated virtue of all former presidents that you could forget about them for weeks at a time,” he adds. “This guy, every 45 minutes, he rings a little bell and you have to go stare at him for a while.”

One way McKibben responded was to step up his writing, producing a mischievous debut novel, Radio Free Vermont, in which his beloved state seeks to secede from the United States.

“Nobody was in the mood for anything dark," he says. "It’s half a love letter to my small quirky home state [that produced Democratic presidential candidate and former socialist mayor Bernie Sanders], and half a kind of mash note to the resistance, of which I’ve sort of been a part for, I guess, 15 years."

“The one good thing to say about the Trump era is that the resistance has grown dramatically.”

His 350.org now employs 100 people around the world, which he claims makes it the biggest such group devoted solely to tackling global warming.

The name refers to the 350 parts per million level of carbon dioxide in the atmosphere considered by some scientists as a "safe concentration" for a stable climate. That's well below the current CO2 level, which is 410-plus and rising.

The group is "a hell of a lot bigger than it was 10 years ago, when I started it with seven college kids," he says.

"But it’s pathetic, you know," McKibben adds with a self-deprecating chuckle. "Any halfway ambitious mid-sized oil companies spends more money lobbying in a quarter than our budget for a year, and there are hundreds of them.”

The future, he says, hinges on a contest between technology, with the promise of renewable energy to displace coal, oil and gas, and the physics of a climate we are shifting.

"Basically, it’s a race, and the job of movements [like 350.org] is to try to make that race come out the right way," he says.  "Left to our own devices, we’ll do [the transition] too slowly. Maybe we can goose the process.”

Two emerging trends offer McKibben some hope. One is the "literal miracle" of a solar panel, which can bring light and communications to poor tropical villages just by taking "a plate of glass and pointing it at the sun",  as he witnessed last year in Ghana .

"They’d just put in, a week before in this rural, remote community, a solar micro grid - maybe an array of 50 panels and the most rudimentary wire into each hut – and they kept handing me cold bottles of water to drink, for which I was grateful because it was very hot.

"But in my predictably clueless Western way, it took me a good 15 minutes to figure out why they would be so proud to be doing it," he adds. "Nobody had ever had a refrigerator. Almost literally, the concept of cold had heretofore been an irrelevant concept."

The other promising development has been "the remarkable emergence of frontline communities in general, and indigenous communities in particular, around the world at the absolute head of this fight” against fossil fuels, McKibben says.

“We work so much alongside and behind our indigenous colleagues everywhere - in Keystone, Standing Rock and Kinder Morgan [pipeline tussles in North America], in the Pacific Islands, in the Adani fight [in Queensland], wherever."

"Standing Rock [in North Dakota] was just an amazing scene" led by Sioux protesters, McKibben says. "And one of the things that made me saddest about Trump’s election was losing that overnight - that pipeline would have been the first constructed pipeline to never go into operation."

As our chat winds down, the waiter comes to inquire as to the satisfaction with our meal, saying he hadn't wanted to disturb our discussion.

"It was really good," McKibben says, joking: “We were literally solving the problems of the world today."

"Good, at least somebody’s doing it," the waiter says with a smile.