In 1992, world leaders signed up to something called "sustainability". Few of them were clear about what it meant; I suspect that many of them had no idea. Perhaps as a result, it did not take long for this concept to mutate into something subtly different: "sustainable development". Then it made a short jump to another term: "sustainable growth". And now, in the 2012 Rio+20 text that world leaders are about to adopt, it has subtly mutated once more: into "sustained growth".

This term crops up 16 times in the document, where it is used interchangeably with sustainability and sustainable development. But if sustainability means anything, it is surely the opposite of sustained growth. Sustained growth on a finite planet is the essence of unsustainability.

As political economist Robert Skidelsky, who comes at this issue from a different angle, observes in the Guardian today:

"Aristotle knew of insatiability only as a personal vice; he had no inkling of the collective, politically orchestrated insatiability that we call economic growth. The civilization of "always more" would have struck him as moral and political madness. And, beyond a certain point, it is also economic madness. This is not just or mainly because we will soon enough run up against the natural limits to growth. It is because we cannot go on for much longer economising on labour faster than we can find new uses for it."

Several of the more outrageous deletions proposed by the United States - such as any mention of rights or equity or of common but differentiated responsibilities - have been rebuffed. In other respects the Obama government's purge has succeeded, striking out such concepts as "unsustainable consumption and production patterns" and the proposed decoupling of economic growth from the use of natural resources.

At least the states due to sign this document haven't ripped up the declarations from the last Earth summit, 20 years ago. But in terms of progress since then, that's as far as it goes. Reaffirming the Rio 1992 commitments is perhaps the most radical principle in the entire declaration.

The cold financial climate of the last three years has made little impact on public attitudes towards global warming, according to a new Guardian/ICM poll.

As the world assembled for the Rio+20 UN sustainable development conference at the end of last week, the survey found that most British voters (57%) accept that man-made climate change is happening. That is one point more than the 56% who took the same view when ICM posed a near-identical question just before the Copenhagen climate conference of 2009.

The poll identified a hardcore of 7% of respondents who deny the planet is getting warmer, two points more than the 5% who said the same at the time of Copenhagen. The proportion who accept the planet is warming but insist this is not principally due to human factors has dwindled slightly, from 33% in December 2009 to 30% today.

The results suggest a remarkable pattern of stability in acceptance of climate change as established fact, a finding which may surprise politicians who have been lowering their environmental ambitions for fear of appearing out of step with hard times. The leaders who went to Rio were so resigned to an insubstantial outcome that they allowed their sherpas to agree the basic communique before they had even arrived.

A follow-up question on impressions of the summit also revealed more continuity than change. Only 17% of voters dismissed the Rio summit as a panic about an exaggerated threat - exactly the same proportion who said the same of Copenhagen.

But if the voters have not moved much, the same cannot be said of politicians. Whereas David Cameron had hailed Copenhagen's "historic importance" as opposition leader, in the months running up to Rio, he licensed his chancellor to argue that "we're not going to save the planet by putting our country out of business".