The only time you could harness wasted energy from a car is when it is braking, a BMW engineer in Munich once told me. Conceivably, this could be done by sinking some sort of energy pick-up into the surface of the road, say at the approach to traffic lights, or by allowing the braking wheels to charge up a battery, and then feeding the stored energy into the grid when you get home.

Listening to former Chief Science Advisor Sir David King addressing a conference on Climate Change Opportunities at the Said Business School this week, I was reminded of this conversation. Perhaps the need to start cutting carbon emissions will put a brake on the world economy; but on the other hand, facing up to the environmental challenges of the 21st century will also present money-making chances galore.

In a town such as Oxford, with its memories of floods last year (even if those floods were not related to climate change, they were certainly reminders of what to expect in future from wetter winters) opportunities for entrepreneurs to earn money from flood defences are perhaps more obvious than elsewhere.

At the conference Sir David, 68, pointed out that there is now more world-warming carbon dioxide in the atmosphere than at any time for 800,000 years. He said it was incumbent on business to change from being seen as the cause of the problem to becoming the "agent for redressing it".

He sees climate change as the greatest threat to civilisation ever, noting that temperatures will continue to rise until mid-century, regardless of what we do now, with average summers by then resembling the record-beating one of 2003.

He said: "For years, we thought that colourless and tasteless carbon dioxide was also harmless. Now we know it is not. And we know, too, that this year there are 387 parts of carbon dioxide per million in the atmosphere and that next year there will be 389."

He added: "And with world population expected to rise from 6.7 billion today to 9 billion by 2050, with many becoming more affluent, tackling potential disaster will be hard."

But he is not full of doom and gloom about science's ability to tackle it. He said: "About half the emissions come from the built environment; but the UK, for one, is committed to making all houses built after 2017 carbon neutral. That is clearly a win-win situation."

But what about the often-asked question: whatever we do here in the developed west, how on earth do we persuade developing and BRIC (Brazil, Russia, India and China) countries to do likewise? Is this not another "tragedy of the commons" - ie, commodities not owned by any single nation - similar to the one that brought about the depletion of fish stocks in common waters?

He answered: "I see the USA's lack of leadership as the most important thing here so far. In the USA, the world's biggest emitter of carbon dioxide, the carbon produced is 27 tonnes per person, in Europe its 11 tonnes, in China six, and India three.

"Obviously, the developed world faces a high bill - but all three US presidential candidates are committed to taking action.

"On the other hand, it is the BRIC countries that face the highest costs from taking no action. When I was the Government adviser, I visited China and worked with Chinese scientists. They are very aware that rising sea levels will threaten Shanghai. Any international agreement will be bound to be difficult, but is not impossible."

In his book The Hot Topic, co-written with the science journalist Gabrielle Walker, he also comes out in favour of nuclear power, arguing that it is essential if Britain is to meet its target of reducing emissions by 60 per cent on 1990 levels by 2050.

Now Sir David is devoting all his time and energy to furthering the cause. In January this year, Oxford University's £80m Smith School of Enterprise and the Environment came into being, with him as its first director, thanks to funding from the Martin Smith Foundation. Its aim is to work closely with business and government leaders to promote a workable response to the challenges of climate change.

At present the school, employing just six people, is housed in Hayes House, George Street, but will shortly move to a larger, Nuffield College- owned building down the street. In October ,the first fellows will arrive and numbers of employees are expected to rise rapidly.

Sir David told The Oxford Times: "Within the next three years, we aim to have a new eye-catching building, probably on the Radcliffe Infirmary site.

"I hope climate change will become a mainstream subject at the university."

But one (former) Government leader with whom Sir David is not pleased at present is former Chancellor of the Exchequer Nigel Lawson. On the desk in front of me as I listened to Sir David at the Said School conference was a newspaper open at a review of Nigel Lawson's new book, An Appeal to Reason: A Cool Look at Global Warming (Duckworth Overlook £9.99 ) in which Lord Lawson hits out at the way green-ness seems to be the received wisdom these days, with dissenters labelled "deniers".

Lord Lawson wrote: "The PC at the heart of the IPCC the International Panel on Climate Change which predicts that temperatures could rise this year by between 1.8 and 4 degrees C as it were, is the most oppressive and intolerant form of political correctness in the western world today."

"Complete and utter nonsense", was Sir David's robust response. "How an economist can comment on science in this way is incredible.

He added: "The IPCC report model upon which scientific predictions are based was headed by the head of the British Met office, the best Met office in the world, used internationally."

For this listener at the conference, even a short spell of listening to a top scientist, rather than economist, was enough to convince me that climate change is happening, that it is man-made, and that if carbon emissions are left unfettered, some 50 million people in China, Malaysia and Bangladesh will be displaced - and that is just for starters. A brake needs to be applied - but the economies of the world can benefit, all the same.