But that is still a distant ambition. In terms of hitching themselves to a model of environmentally sustainable progress, Copenhagen delegates are still haggling over the prenuptial agreement.
Why the cold feet? The problems divide into three broad categories.
First is money. On a simple cost-benefit analysis, the best value lies in substantial and early action, as Sir Nicholas Stern’s landmark report in 2006 found. The price of dealing with natural disasters and population movements triggered by global warming in the future is higher than the price of cutting emissions today.
But at Copenhagen the question of cost cuts across delicate diplomatic lines. It is broadly recognised that countries that have already industrialised, and so already pumped billions of tonnes of carbon into the atmosphere, ought to subsidise the transition to greener energy elsewhere. But there is no agreement on how big the subsidy should be or how the transfer will be managed. The idea of western taxpayers, for example, helping the Chinese to develop competitive new green technology is not an easy sell in the US Senate.
There lies the second problem: politics. A global treaty to limit emissions would require a global enforcement regime to ensure its provisions were met. That means some submission of national governments to international authorities, possibly with inspections and sanctions of some kind. The US has always been virulently opposed to any such implied subordination. But without US participation a climate deal is practically useless.
Meanwhile, the prospect, however distant, of a global climate governance regime will surely fire the growing anti-environmentalism movement to new excesses of paranoia.
And that is the third problem: denial of the science. The opponents of a climate deal are newly emboldened by the recent publication of hacked emails from a leading research centre, purporting to show manipulation of data and intent to suppress dissenting opinion. In fact, the emails, taken in the context of a vast and uncontroversial body of correspondence, prove nothing. They demonstrate, at worst, a cavalier prejudice against work that the correspondents deemed shoddy. They categorically fail to show the case for man-made climate change is flawed, or even exaggerated.
The climate conspiracy theory falls apart when you consider the effort that would be required to sustain such a scam (recruiting thousands of scientists, falsifying mountains of data) and then ask what plausible motivation there could be to continue such a vast conspiratorial effort? None, is the simple answer.
Man-made climate change is real. Copenhagen is clearly not the last major climate summit of its kind, but it must be the last one conducted in an atmosphere of public debate where science is still fighting a rearguard action against nonsense.
It must also be the last summit where binding treaty obligations are deferred. The scientific case for action is irrefutable. So is the economic case. That just leaves the politics, where courage is the deficient commodity. The prenuptial talks have gone on too long already. The time has come to exchange the necessary vows.