Leading article: The green giant awakes

Robin Cook used to call the environment "the sleeping giant of British politics". Perhaps last week was the one in which the lethargic leviathan woke up. On successive days, both likely next prime ministers - David Cameron and Gordon Brown - delivered long and meaty speeches putting global warming at the top of their agendas. Mr Cameron visited the Arctic Circle to see it happening for himself, accompanied by his environment spokesman, Greg Barker - who, as we report today, first sold his Porsche, presumably better to travel by eco-friendly dog-sled. And Mr Brown dutifully picked up the message of our leading article last week by declaring that tackling the climate change is a "moral duty".

If the giant is indeed stirring, it is Mr Cameron who has poked him in the eye. Whether out of conviction or, more likely, because Mr Cameron has spotted an electoral opportunity, he has made the environment his trademark since winning his party's leadership. Last week, before heading north, he launched the final stage of his local government campaign under the slogan "Vote Blue, Go Green". On his way back, he delivered a thoughtful speech on climate change in Oslo which should help lay to rest the charge that his approach is all spin and no substance. He backed the Kyoto Protocol - in contrast to Tony Blair's wobbling - and laid out concrete policies for the future.

Mr Brown appears to be playing catch-up. That impression is not entirely fair: stimulated by the horrific impact that the climate change will have on the world's poor, the Chancellor was exhibiting increasing interest long before Mr Cameron. But it was not until the end of last week that he nailed his new green colours to the recycled wood mast. He did so in the US, complete with an implied rebuke to President Bush - something that, despite much urging, the Prime Minister has failed to deliver. Yet going on to Washington, he also extolled the importance of increasing production of the very oil that is fuelling the looming climate catastrophe.

So now the giant is awake, what should he deliver? Mr Cameron is right that green taxes are an important part of the solution. They make economic, as well as environmental sense. Shifting the burden of tax from "goods" such as employment to "bads" such as pollution, would increase employment as well as combat climate change. Mr Brown agrees, and indeed promised to boost them before taking office - but under his stewardship they have actually decreased. He did introduce the climate change levy on industry - and got small thanks for it from environmentalists while being denounced by those affected. But, scandalously, he scrapped automatic increases in petrol prices in the face of the fuel price protests in 2000 (again green groups got it wrong by bottling out of making the case for the tax when it was under assault).

So Mr Brown must finally put the taxpayers' money where his mouth was. He should also back tough caps on pollution from British industry under the EU emissions trading scheme, which allows countries to buy and sell permits to pollute within set limits and which he vigorously backed in his speech. And both he and Mr Cameron face an early test over nuclear power. The atom, as repeated studies are showing, is more likely to hinder than help the fight against climate change by stifling renewable alternatives. There are signs that Mr Cameron is prepared to abandon his party's long commitment to it (although Zac Goldsmith - his once fiercely anti-nuclear adviser - seems to be travelling in the other direction). Mr Brown is also sceptical. Between them they could stop Britain from heading down this dangerous blind alley. Then we would know the green giant is truly awake.