Stop economic growth in its tracks, start living locally, at a slower pace, and share more - that was the remarkable demand yesterday at the beginning of the Sustainable Planet Forum, a three-day international conference on environmental issues in the French city of Lyon, which The Independent is co-sponsoring.
In the radical corner was Paul Ariès, one of France's more colourful political figures, an anti-globalization campaigner who edits a magazine entitled Le Sarkophage, which is a French pun on the word for coffin and the name of the President of the Republic, Nicolas Sarkozy. (You can guess the content.)
In the Conservative corner was Peter Ainsworth, the former shadow Environment Secretary who left Parliament at the last election after 18 years as the MP for East Surrey. He is active on numerous environmental issues and has long been seen by environmentalists in Britain as the epitome of a Green Tory.
Immediately after the forum's opening ceremony, they clashed in the main auditorium of the Lyon Opera House before an audience of nearly 1,000 intent listeners, many of them young. It's an indication of how popular in France such think-fests are - this one being organized by the French daily Libération, in co-operation with The Independent and Italian newspaper La Repubblica.
The Sustainable Planet Forum is focusing on the issue of sustainable development - how we can provide for our needs without stopping future generations from satisfying needs of their own (and without wrecking the planet) - which until less than a decade ago was the animating cause of the environment movement, until concern for climate change swept everything before it. The forum also has an underlying subsidiary theme, which is Europe and its future.
But it was the idea of economic growth, or rather degrowth, to use the term of Mr Ariès - décroissance - which set the debates going with a bang. The French thinker is not just opposed to economic growth, but actively wants to stop it, seeing it as the root of all our evils. In fact, he is opposed to sustainable development, as - to paraphrase his thought - for him, the development bit cancels out the worth of the sustainable bit.
Economic growth, he told the audience, inevitably leads to social inequality. Mr Ariès wants a new sort of society, organised locally, at a slower pace, based on sharing rather than exploitation, and if you take his thought to its logical conclusion, virtually shrinking.
He expressed it yesterday from the stage of the Opera House with a finger-jabbing and strident passion which at times verged on the excitable, and was in sharp contrast to the dry but powerful response of Mr Ainsworth, who told him to his face: "You are a dreamer."
"Vous êtes un rêveur," said the interpreter, just in case Mr Ariès had missed it in English. He certainly didn't look like he got told that an awful lot, and Mr Ainsworth hastened to add that society needed dreamers. But he launched a full-frontal assault on his opponent's degrowth idea, based in what you might call a Conservative view of human nature.
He said: "Humans are acquisitive; we always have been. It's a fair bet that when we originally crawled out of a cave in prehistory we went looking for stuff to accumulate. Another pelt; a better home; a sharper weapon; a longer stick. Stuff: it's what people like."
That word stuff caused the interpreter a momentary hesitation, but Mr Ainsworth was already saying: "The people who live in the poorest parts of the world don't talk about poverty. They live with it. The notion of poverty is for the affluent to worry about, and rightly so. But people who live in real poverty, whether in the deprived cities or rural areas of the developed West or in the developing world, talk about prosperity. They want economic growth because it is a natural thing to want. They want more stuff."
A recent visit to Albania, one of Europe's poorest countries, had impressed this upon him, he said.
"Try telling people in Albania you want to offer them degrowth. You won't get a friendly answer."
Mr Ainsworth said he shared many of Mr Ariès' concerns about overexploitation and overconsumption, pointing out: "If everyone on our planet lived like an average European, we would need three planets to live on. If everyone had the lifestyle of an average citizen of the United States, we would need five planets to live on."
But he said degrowth was not the answer. The only solution was to grow in a different way - that was what sustainable development meant - and the only institutions who could enable us to do that were major companies, with innovations.
Mr Ariès responded that he wasn't looking to Coca-Cola to save the planet - his best line, which drew laughter and applause - but Mr Ainsworth insisted that it was only new technological advances ("game-changers" he called them) which would set growth on a different path. "You want to save the planet with gadgets!" cried a woman in the audience. "The electric car is not a gadget," Mr Ainsworth said.
His finished by telling Mr Ariès that the ultimate problem with his degrowth idea was political. "No democratic politician anywhere in the world will embrace it," he said. "Call that cowardice, or call it realism." And turning to the audience: "You choose."