The United States consumer is the "engine of the global economy". If the Americans stop buying, that engine will "stall". Or so we have been told repeatedly in the past few weeks. Yet, it would take the resources of more than five planets like Earth if everyone shopped like America. The problem, rather, is that if the US "over-consumer" keeps on shopping, we face the much worse scenario of all the planet's human life-support systems stalling.
Relying on an environmentally suicidal model of consumerism to deliver fulfilment is both a non-starter and a contradiction in terms. But it leads to a question that the political mainstream and the British left (old, new, or any other type) seems incapable not only of answering, but of bringing itself to ask. How can more than six billion people have their needs met and get the chance of a good life, without wrecking the natural systems on which we depend?
The good news in wealthy countries is that satisfaction with life has nothing to do with rising consumption. In the UK, while our economy has grown consistently over the past few decades, our well-being has flatlined.
A recent New Economics Foundation survey of more than 35,000 people from across Britain and Europe revealed widely varying levels of consumption - from very low, so-called "one-planet living" to very high "seven-planet living". The staggering finding, however, was virtually no connection at all between life satisfaction and consumption levels.
But shooting the messengers of eco-friendly good times has become a popular sport (see the review of Oliver James's The Selfish Capitalist in last week's New Statesman). The irony is that the founding economic texts of both left and right saw through the false promise of conspicuous consumption right from the start.
Adam Smith mocked lovers of luxury who "walk about loaded with a multitude of baubles . . . all of which might at all times be very well spared, and of which the whole utility is certainly not worth the fatigue of bearing the burden". Karl Marx laid bare the inevitable treadmill and trap of dissatisfaction behind purely material ambitions: "A house may be large or small; as long as the neighbouring houses are equally small, it satisfies all social requirement for a dwelling. But let a palace arise beside the little house, and it shrinks the house to a hut."
New systems of measurement now allow us to assess the efficiency with which scarce natural resources are converted into human well-being, measured in terms of life expectancy and satisfaction. With policies to maximise that efficiency, instead of crude overconsumption, good lives needn't cost the earth.
Andrew Simms is policy director of the New Economics Foundation and co-editor, with Joe Smith, of "Do Good Lives Have to Cost the Earth?" (Constable, £7.99)