Leading article: The climate change circus rolls on

In assessing the importance of the climate change agreement made in Cancun yesterday, we should not confuse relief with genuine cause for celebration. The talks did not break down in acrimonious failure, which would have been bad for the prospects of humankind's sustainable stewardship of the planet. But the hailing of the deal at Cancun as a "breakthrough" is premature and excessively enthusiastic. The essence of the deal was that all countries (apart from Bolivia and Cuba) agreed not to call it a failure. Yet discussion of all the difficult issues was postponed for resolution at a later date.

In this, the Mexico summit represented a triumph of the management of expectations. After the heady millenarianism that preceded the Copenhagen conference a year ago, only to be brought down by the intransigence of the Chinese government (behind which hid the Indians and others), no one held out much hope that anything substantive could be agreed at Cancun. So, when the 193 countries reaffirmed this, committed themselves in principle to that, and expressed a determination to go on talking all the way to the next stop, Durban in South Africa, this was better than what might have been.

So the caravan rumbles on; the show stays on the road; the bicycle stays upright. All the staple metaphors of UN climate-change negotiation commentary remain in play. We are all still aboard the train; the travelling circus is still in business. This time next year it is Durban (mind you, type Cancun and South Africa into Google and the first site that comes up offers cheap flights from one to the other). It has become an annual event, with an Olympics or World-Cup-style competition to stage the next one. Qatar, appropriately enough, is in the running to provide the venue for the summit in 2012.

However, simply keeping a vast itinerant bureaucracy in being is not the point of the exercise. The ultimate question is how much the governments of the world succeed in reducing the carbon intensity of economic activity, and so far little has been achieved beyond the vagaries of switching energy sources and the steady march of technological efficiency. The key drivers of greenhouse gas output remain population growth and the economic cycle. At each conference, the participants agree a form of words and express the shining hope that the binding details can be nailed down by the time of the next one.

Of course, that is better than the alternative, which is to give up on negotiations that seek to include all the countries of the world. And, of course, we have to accept that progress in such a complex global endeavour will be painfully slow. Indeed, if we adopt a wider perspective, and strip out the expectations effect, it can be seen that Copenhagen was more successful, and Cancun less so, than the contemporary perception.

Anthony Seldon, in his instant history of Gordon Brown's government, comments, "In hindsight, the Copenhagen accord looks better than it did at the time." Within six months, most of the world's major economies, responsible for 80 per cent of global emissions, had written into it their commitments to cut emissions.

By contrast, and although progress was made at Cancun on difficult issues such as the need to account for the world's forests, little new was agreed yesterday. For example, the fate of the Kyoto protocol, the main legally binding climate-change agreement, which expires in 2012, was not decided. Much of the rest, such as more details of the scheme by which rich countries subsidise the efforts of poorer nations to curb their emissions, was a matter of elaborating the Copenhagen accord.

Let us not be churlish. Reaffirming rhetorical commitment is the precursor of practical action. Parochially, David Cameron's response to yesterday's agreement was to repeat his aspiration, saying, "This will be the greenest ever British Government." That makes it just a little harder for him to slide farther backwards. Greg Barker, the junior Climate Change minister, also made an important point when he said: "Cancun will send a strong signal of confidence to business investing billions in the new global green economy."

Keeping the travelling circus on the road is critical to confidence, and it is only if people and businesses worldwide believe that carbon-based energy will become more expensive in future that deep long-term changes will happen.

The Cancun agreement is better than nothing, but it is not enough.