It would not have been surprising to find that Tim Flannery was smug as well as green. He is, after all, a global man of the moment as well as Australian of the Year 2007. The world - even George W. Bush - is finally starting to heed warnings from Flannery and fellow scientists about the dire consequences of climate change.

Biologist, palaeontologist, explorer (he described 29 new species of living and fossil kangaroos) and successful author, he is now best known for his efforts to curb -runaway global warming. Like all good greens, he has plenty of facial hair.

The bearded professor is bound to be a vegetarian, I think, but he immediately proves me wrong when we order dinner at Shui Hu Ju, a Chinese restaurant in the heart of Hong Kong’s SoHo district, which serves robust, traditional food, the beer served in clay bowls on tables of lacquered wood. Flannery is on his way to Europe to help launch a new pressure group called the Copenhagen Climate Council. It is in the Danish capital that the vital successor agreement to the Kyoto Protocol on climate change will be negotiated in 2009.

Flannery is not smug. He is worried. ”We want a better outcome than we got for Kyoto, which was bloody appalling. And when you see the way these meetings work, everyone is arguing from self interest. So we thought we’d try to run a parallel process to lay out clearly the moral case for strong emissions reductions. For us, and I think most of the scientific world, 450 parts per million [of carbon dioxide in the atmosphere] is a serious threshold that we don’t want to cross.”

That is a tall order, given that the greenhouse gas content of our air is already up to 420ppm (these figures include CO2 and other greenhouse gases expressed in terms of CO2 ), and is continuing to rise rapidly as a result of humanity’s addiction to coal and oil. I ask whether he is, nevertheless, pleased that world opinion on global warming is moving fast in his direction - even in his native Australia, where John Howard, the prime minister, has been an loyal ally of Bush in the anti-Kyoto brigade.

Pausing to admire a dish of prawns in a mouthwatering egg-yolk sauce, Flannery shakes his head. ”Some of the leading nations are certainly making the right sort of sounds, but there are a huge number of others which are not moving in the right direction, or at least not fast enough. Despite our best efforts we’re headed rapidly in the wrong direction. We’re coming very rapidly to a crisis point. I don’t think anyone of good conscience can look at the data and say, ’Oh, it’s going to be okay.’”

Flannery denies insulting Howard when the prime minister performed the uncomfortable task of giving him the Australian of the Year award. ”I said I would be relentless in pursuit of [climate change], and anything I saw as bad to do with decisions or foot-dragging, I’d speak out about it. I couldn’t see his face but he looked unhappy according to those who did see.” He laughs. ”It wasn’t specifically directed at him. Both parties have their problems in Australia.”

We start on our second bottle of Tsingtao beer and I ask him if he finds it depressing to be a prophet of doom. Flannery - who wrote Throwim Way Leg (New Guinea pidgin for going on a journey) about his jungle adventures long before he addressed climate change in his recent book, The Weather Makers - admits it was ”a huge amount more fun” being an explorer.

Yet he does not despair. ”I’m naturally a pretty cheerful person and that helps. But you have to create a sort of an escape, and that for me is doing a bit of creative writing, to create a fiction world I can escape in to. I haven’t published anything yet. At the moment I’m just writing a black comedy about death.” I burst out laughing, pointing out that this is hardly a cheerful subject, but Flannery the novelist-to-be is adamant that the death of a heavy-smoking real-estate agent who has tried to change his life is very Australian and very funny.

”Extraordinary - serious chillis!” Flannery interjects as we are presented with a huge platter of flaming red Sichuan chillis piled over chunks of spicy black chicken.

The conversation quickly returns to the serious business of the future. At 51, Flannery has two children, aged 20 and 22, who are ”environmentally aware”. But he is surprised that there is not more radicalism among the young - he recalls the firebombing of a Hummer dealership in California in 2003 - given the way their parents have bungled the stewardship of the Earth and its fragile atmosphere.

Underlying Flannery’s message is a fear that global warming will reach a tipping point beyond which recovery will be impossible. ”I think it’s going to be a bit like a heart attack,” he says. ”You can go along for a very long time if you’ve got a bad heart condition and live a relatively normal life, because at the start you accommodate it and you change your lifestyle. But then you have quite a serious shift, a changing condition. All the projections are that some time this century there will be no more Arctic ice cap and when that happens (the ice cap helps structure the climate system for the whole northern hemisphere) we’ll see some really significant changes.

”The fact that the Sahara desert is where it is, is due to the temperature gradient between the pole and the equator. One could change that temperature gradient by warming the poles significantly, and who knows how those systems are going to react. If you look back in the geological record, you will see there were times when Greenland was covered in rainforest and the tropics were uninhabitable.”

He brushes off my mention of the environmental sceptics, such as the statistician Bjorn Lomborg, and their contention that money would be better spent on helping the poor than on the uncertain benefits of combating climate change. Global warming, says Flannery, will accelerate the spread of tropical diseases and reduce the availability of water and food. He contends that the widely used official projections of the Intergovernmental Panel on Climate Change have proved to be too conservative, with data from the real world for factors such as CO2 accumulation or the loss of sea ice in many cases exceeding the upper limits of recent predictions. ”At the moment we’re running an inadvertent experiment,” he says. I am struggling to hear his scientific explanations above the hubbub of the restaurant. ”The way I try to explain it is that the metabolism of the -fossil-fuel-based economy is on a collision course with the metabolism of the Earth.”

What, then, is the solution, given that neither Chinese peasants nor European steelworkers nor American investment bankers seem particularly interested in biodiversity or the loss of thousands of animal and plant species? Is population control the answer? Flannery has suggested that the maximum number of inhabitants in Australia ought to be six million, not 20.4 million. ”I have stopped talking about population in Australia or anywhere,” he sighs, ”partly because I don’t think it’s a solution to the climate change problem. Climate change is moving so quickly that it’s got 20 per cent worse in a decade. Population doesn’t move that fast.”

Flannery is not shy of radical ideas. He recommends the imposition of carbon tariffs on trading nations that fail to pull their weight in repairing the global climate. He thinks Australia should abandon the mining and burning of the coal that produces most of its electricity and a share of its exports, and rely on other forms of energy such as solar and geothermal power. And, he believes, it will not be long before business people who knowingly pollute the air with excessive CO2 (by running energy inefficient buildings, for example) are called to account as ”climate criminals”. At the planetary level - assuming neither total catastrophe nor complete success in curbing greenhouse gas emissions - he foresees the need for a kind of super-Kyoto he calls an Earth Commission for Thermostatic Control.

But are we not all responsible as individuals? Is he not about to jet off to Copenhagen in a carbon-spewing airliner?

He admits that the carbon offsets he buys to compensate for his flights do not make him comfortable. But he owns a hybrid car, he says, and produces all his electricity at home from solar panels without the need for a back-up generator. His moment of truth came a few years back when he was showering in a flat in Adelaide. ”It was a summer’s morning, it was already about 30 degrees [centigrade] outside and I thought, this water is being heated by burning coal 300km away, wastefully transmitting electricity through to my bloody house. And I thought, this is intolerable, this is the most immoral shower I’ve ever had. So I went out and bought a solar hot water system.”

After two hours of meaty conversation on what is probably the most important issue facing the world today, our meal draws to a close. Before we part outside in the hot Hong Kong night, he surprises me with the tentative suggestion - even naive, I think - that humanity’s need to co-operate to survive could make wars unthinkable.

”If we do manage to broker a genuine, international, binding protocol to deal with these air-pollution issues, we will be acting as a species for the first time - for our own good as a species,” he concludes. That -comment makes me think of the grim, unanswered question at the heart of a book by another popular science writer, Jared Diamond. Several civilisations extinguished themselves by destroying their environments, he argued in Collapse. Surely humanity as a whole would not be stupid enough to destroy the environment of the planet?

Flannery says climate change is really the only issue we should worry about for the next decade or so, but he will not be drawn on how hopeful he is of success. ”I’m not optimistic or pessimistic. I’m just very determined to make a difference.” For all our sakes, I hope he does.

Victor Mallet is the FT’s Asia editor.

Shui Hu Ju, Hong Kong

1 x wok-fried prawns with crab roe

1 x deep-fried black chicken

1 x fried squid with golden garlic

1 x wok-fried jade vegetable

2 x steamed rice

5 x Tsingtao beer

1 x bottled water

Total: HK$924 (£60)