Leading article: Cancun: Where's green Dave now?

Remember the environment? This newspaper does. The Prime Minister, on the other hand, seems to have forgotten his promise after the election to lead "the greenest government ever". There is an obvious explanation for his early onset amnesia, which is that the voters have become markedly less willing to make personal sacrifices for the sake of a distant, global objective in times of economic stringency. But that is precisely the kind of opportunism to which we feared that David Cameron was prey when he posed on a sled in the Arctic or insisted that the recession made it more important that he stuck to his green message, not less.

He talked a good green game in opposition, but so far his main claim to environmental credentials in government consists of not doing something – cancelling the third runway at Heathrow. And it could give an unfortunate impression that one of the few announcements by a Conservative minister in the Government was Caroline Spelman's policy of helping the country to adapt to climate change rather than trying to stop it. It is actually a sensible policy, given the amount of warming that is already in the global climate system. But we must press ahead with mitigation at the same time as adaptation, in the jargon of policy-makers.

It has been left to Chris Huhne, the Liberal Democrat Secretary of State for Energy and Climate Change, to push ahead with bringing some economic rigour to Britain's planning for its own low-carbon future. This he has done with some skill. Last month The Independent on Sunday reported that he had dropped the plan for a tidal barrage across the Severn; its electricity would have been simply too expensive compared with other forms of renewable energy. Hard-headed green economics – one of Mr Huhne's Mastermind special subjects – dictates that nuclear power, clean coal and wind farms should form the core of future electricity generation.

Mr Huhne also represents the nation at the Cancun summit, which starts tomorrow, about which he writes today. In effect, his message is that we should not expect much of this latest stop of the caravan of climate-change summitry, as it lumbers from Rio 1992 via Kyoto 1997 and Copenhagen last year, but that the momentum will take us to the promised land eventually. Well, it is telling how an impatient idealist who would have castigated ministers for such a plea for "a little time" turns to such language when he becomes a minister himself. But that is politics, and Mr Huhne is one of the more capable ministers when it comes to negotiating complex global agreements.

However, his article raises wider issues about the climate change agenda. It is not, as we have pointed out before, simply a narrow matter of energy policy. The obstacle to a bold low-carbon energy policy, for example, is ultimately the question of fairness, in that low-income households will have to pay more for their energy. That requires the Treasury to be involved. And the point about climate-change summits, as Gordon Brown learnt at Copenhagen, is that, after decades in which the United States was the villain of the piece, China is the main holdout against a legally binding global treaty now.

Realistically, British influence on the closed Chinese political system is limited, even as part of the European Union. But the point is that for Britain to have a chance of any role whatsoever on the world stage, action on climate change must be pressed by the Foreign Secretary and Prime Minister. Yet on the multi-ministerial visit-cum-trade mission to Beijing earlier this month, it cannot be said that climate change was at the forefront of the British pitch.

Mr Huhne is doing good and important work, but until a sense of green purpose is rediscovered at prime ministerial level, the Government will play no more than the role of a well-informed facilitator in international talks. For that, we need to look to Mr Cameron and his deputy, Nick Clegg, another politician who talked a green game in opposition, but whose interest in the issue in office has not been easily discernible by the naked eye.

If the Liberal Democrats are agonising about their party's purpose, after all the compromises required by coalition politics, they could do worse than to see their role as being to keep the Government honest on the green agenda over the coming years.