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The future has become a playground for competitively minded pessimists …

"You wait until the oil runs out, pal; once the global resource wars are over, the survivors will be going to work on horseback …"

"No more petrol? World war? That's a picnic. When global warming kicks in the entire population of North Africa is sailing to Europe …"

"Mass migration and famine? A doddle. Once we run out of kerosene and there're no more planes, all the crap in the air that helps keep us cool is going to blow away, leaving most of the Earth a scorched wasteland …"

This last point was made by James Lovelock, the originator of the Gaia hypothesis and comfortable winner of the pessimism Palme d'Or. He wrote in The Independent recently that "before this century is over, billions of us will die, and the few breeding pairs of people that survive will be in the Arctic". So, we're not talking about the mere collapse of civilisation, but the near extinction of the species.

What does the other side say? Well, even the US' Optimist-in-Chief recently warned the American people that their addiction to cheap oil was undermining their future. Coming from George W Bush, the president that Big Oil made, this was chilling news. And an indication that a political tipping point may have been reached. Talking of which, didn't Margaret Becket tell the Today programme last week that the public should be aware that "we could come to a tipping point where change could be irreversible"?

The Edge debate, held at the Institution of Civil a couple of weeks ago, was conducted in the sombre shadow of Lovelock's article. The subject was the need to control energy demand so as to ameliorate the effects of atmospheric carbon and eke out the oil and gas that remains.

The climate change debate used to be about whether or not global warming was happening. We appear to have moved on. The sense of the meeting was that climate change cannot now be stopped: the physical forces that are causing it are too powerful and too far advanced. The debate is rather about how long we have left: is it going to affect our children or merely our grandchildren?

Colin Challen MP offered some encouraging figures from a recent poll that suggested that 69% of people agree with reducing energy consumption and 98% want action to be taken (62% thought strong action, 36% thought some action). Challen has recently launched the Climate Change (Contraction and Convergence) Bill. This recognises that there is an upper limit to the amount of CO2 the atmosphere can absorb and when we can agree what it is we should cap our emissions at this point and create a system whereby those who don't use their full carbon entitlement can trade with those who do. The mechanism for doing this would be domestic tradable quotas (another of Challen's bills).

This proposal has intellectual elegance, but did you see the reports last week of a rift between the DTI and DEFRA over the European Union's existing emissions trading scheme? It seems that The DTI wanted to cut no more than 3 million tonnes from the UK's carbon allowance between 2008 and 2012, whereas DEFRA is pushing for 8 million tonnes.

At the global level, intergovernmental structures based on treaties are too weak to make states change their behaviour. According to another speaker, Chris Beauman, a senior adviser to the European Bank of Reconstruction and Development, greenhouse gas emissions will rise 57% between 2000 and 2025. Beauman explored the Pacala and Socolow position on solving climate change through technology. This approach asks one to take a handful of the 14 or so carbon-reduction technologies on offer and to back those. It is about knowing which ones to back and which combinations work well together. The built environment ought to have a view.

David Fisk, professor of engineering for sustainable development at Imperial College, was the final speaker. What, he wanted to know, would you do if the population said: "Got no permits … Am I f* bothered?"

His thesis was that energy efficiency has to be sold the way Marlboro sells something as unsexy as a cigarette: by making it sexy. He argued that we think we have choice in the market but we don't. Paradoxically, we are given too much choice to ever be able to decide. We work instead to a narrative that the ad man gives us. The stock example here is district heating, which is an indicator of middle-class status in Sweden and underclass status in the UK.

The point here is that if you're looking for mechanisms for changing mass behaviour - emotional tipping points - it won't be enough to issue warnings on the Today programme, or to wait until the effects of climate change are visible with the naked eye. What you need to rely on is fashion, and fashion is driven by desire.

So the final question to consider is this: how do you make people desire low-energy lives?

Any ideas?