The UN climate change talks in Cancun are "poised on a knife edge" as they enter their final day this morning, with the possibility of success, but also the possibility of "a car crash," according to Britain's Energy and Climate Change Secretary, Chris Huhne.

A couple walks past a bottle with a message placed by Oxfam activists during a demonstration in Cancún, Quintana Roo State, Mexico, last month. (Photograph: Ronaldo Schemidt/AFP/Getty Images) Mr Huhne, who is leading a special group of ministers tackling the meeting's key problem - how to replace the current international climate treaty, the Kyoto Protocol - gave a solemn warning last night that the conference could very possibly end in outright failure, as happened at Copenhagen last year.

Such an outcome would be "very very serious" not only for the issue of global warming, but also for the whole UN process which has been set up to deal with it, he said, and it would risk turning future talks into a "zombie conference", at which there would nobody of sufficient seniority in attendance to take any serious decisions.

Mr Huhne is leading a group which includes ministers from Brazil, New Zealand and Indonesia on tackling the Cancun's most intractable problem - how to resolve the split between rich countries and poor countries over Kyoto, which runs out at the end of 2012.

For two weeks at Cancun's luxury Moon Palace hotel complex, while 15,000 delegates from nearly 200 nations have been discussing all aspects of a new climate deal, from a treaty to prevent deforestation to a new global Green Fund which could give developing countries billions of dollars annually in climate aid, Kyoto has remained the central question, threatening to undermine everything else.

Signed in the Japanese city in 1997, the treaty makes the rich industrialised countries take on legally-binding commitments to cut their emissions of greenhouse gases, while imposing no such commitment on the poorer developing nations.

The developing countries are fiercely attached to it, not only for self-interest - although that is clearly part of it - but also because they see it as an earnest sign of the rich countries' continuing good intent in tackling the climate problem and they want there to be a so-called "second commitment period" of the protocol, binding the industrialised nations to new and tougher targets for cutting their emissions, while they themselves are still legally obliged to do nothing.

The rich countries want a new treaty which binds everybody to cut their CO2 and it was essentially over this difference that Copenhagen collapsed.

It was hoped that a compromise could be found in Mexico - Britain and the European Union would now accept a renewed Kyoto, as long as there is a separate, parallel agreement which binds everybody - but on the opening day the Japanese electrified the conference by asserting in unusually strong language that "under no circumstances" would they consent to renewing the treaty signed in their historic city.

They were joined in their stance by Russia and Canada, who are also refusing to sign up again.

They were met with a fierce response from the conference's most radical grouping, the "Alba" group of socialist Latin American states, who insisted that without a new Kyoto, there would be no deal.

These positions have become entrenched and Mr Huhne has spent the last three days leading the special group set up to try to bring them together, but yesterday he said that in essence the two sides were still far apart and unless people gave ground, the conference would end in deadlock.

"The issue is whether countries that are on the extremes about this are prepared to recognise that they're not going to get what they want in its entirety here in Cancun," he said.

There was "a deal to be had", on many aspects of climate change, but it could would not be done without some sort of resolution of the question of Kyoto and a future parallel treaty binding everyone.

He disclosed that David Cameron was seeking to be in direct contact with the Japanese Prime Minister, Mr Naoto Kan, as was the Mexican President, Felipe Calderon, to see if the Japanese position could be softened.

Referring more than once to the possibility of a "car crash" at the end of today, Mr Huhne said: "I think the consequences would be very very serious and very worrying. "Obviously the science on climate change is getting more worrying, not less; the evidence over the last year has got stronger for anthropogenic climate change, and we really do have a very limited window in which we have to move forward globally to get emissions down - if we don't do that, we are going to lose any real prospect of holding temperatures to below two degrees above pre-industrial levels." [regarded as the danger threshold for the world.]

He went on: "I think the other element which is very worrying, is that if there is a failure here, the whole question of the effectiveness of the United Nations process at coming up with solutions to global problems, is going to get called into question. And the worrying scenario there will be that this process becomes a sort of zombie conference, where there won't actually be anybody able to be at a senior enough level to take any serious decisions at all. So the stakes are extremely high here, both for climate change, because this is the pre-eminent global problem, and for our existing means of dealing with global problems - the UN process."

The reason why Kyoto is no longer acceptable to some nations now, when it was signed by all the world community in 1997, lies in changing circumstances. The agreed basis on which it was constructed was that "parties should protect the climate system ... in accordance with their common but differentiated responsibilities".

What "common but differentiated responsibilities" means is that we're all in this global warming business together, but some of us have done, and are doing, a lot more to cause it than some others, and on that basis, we should bear the lion's share of putting it right. We, of course, are the industrialised countries. Most of the excess carbon dioxide in the atmosphere which is causing climate change was put there by us, in the two fossil-fuel-burning centuries since the Industrial Revolution began in Britain, and when the original UN Climate Convention was being drawn up, between 1990 and 1992, not only did we have the historical responsibility, we had the present responsibility.

If you look at the left-hand side of the graph on this page you can see how CO2 emissions were divided up in 1990: America, the blue chunk at the bottom of the graph, was overwhelmingly the world's biggest single polluter, emitting 25 per cent of the world's CO2 for less than five per cent of the world's population. The major, OECD countries of Europe were next, with something approaching 20 per cent, and the industrialised world as a whole, which ends with the green band, was emitting between two-thirds and three-quarters of the total; the developing countries were far, far behind, and even the emissions of China, the largest, were less than half those of the US.

Under these circumstances, who could argue against common but differentiated responsibilities? Who could gainsay the fact that we in the industrialised world had not only done most to cause the problem, we were still doing it and therefore should do most to put things right? And if you go back to the graph and use a ruler or a sheet of paper to see where countries were in 1997, you can see that it was still the case, as the Kyoto deal was being negotiated in the city of a thousand temples, that the industrialised world was emitting far more than the developing world was.

But then the graph starts to change radically: developing world emissions begin to shoot up, those of China above all. Chinese carbon emissions doubled, from three to six billion tones from 1996 to 2006, and in 2007 they overtook the US, the biggest polluter of all. Now go back to the graph and look at this year, 2010: the industrialised world and developing country emissions are nearly equal (and they will be soon); then look at the projections for 2030: the developing world is well ahead, and its emissions are shooting away from those of the industrialised nations, growing far faster. This colossal, historical shift has thrown a spanner in the works of the UN climate mechanism, because it undermines the idea of common but differentiated responsibilities, as the key organising principle. It may not undermine the principle itself, but it certainly undermines its universal acceptance, in so far as it means that the industrialised world should do everything and the developing world should do nothing. For even if the historical responsibility of the rich world remains - as it does - what are we to do about the present?

Are the huge developing country emissions simply to be ignored?

Some countries such as Japan will no longer accept this, and the split has become a fault line which now bisects the world's climate change machinery, and which, if agreement cannot be reached in Cancun by tonight, will become unmistakeably visible.