Leading article: The tipping point

Maybe, just maybe, we are about to reach the most crucial tipping point in the fight against global warming. Not the scientific one, where climate change escalates irreversibly out of control; with luck, we have some 10 years in which to avoid that, though - as Sir Richard Branson points out on page 13 today - we should all pray that we have not passed it already. But the political one where, at long last, the world wakes up to the unprecedented dangers we face and belatedly begins to take action.

Last week showed signs that we might be approaching it. Sir Richard himself - a sceptic on global warming a year ago - announced that he was to invest $3bn in trying to "kick-start" a new green alternative fuel industry. The Liberal Democrats finally began to reclaim the green soul they had largely lost under Charles Kennedy by adopting Britain's most comprehensive proposals yet on environmental taxation. And, as we report on page 14, Yvette Cooper - one of the most promising of the younger generation of Labour ministers - is drawing up plans to turn British houses from the most polluting in Europe to the most eco-friendly.

It is the same story even in Australia and the United States, the two countries that flatly refused to have anything to do with the Kyoto Protocol, the only international agreement on slowing down climate change. Down under, the environment minister, Ian Campbell, praised Al Gore's documentary An Inconvenient Truth in defiance of his Prime Minister, John Howard, who had sniffed that he did not "take policy advice from films". Across the Atlantic, California sued the six largest car firms in the US for contributing to global warming, and started a missionary programme to export its own pollution curbs to other states. The US head of the oil company Shell was storming round the country saying that "the time for debate is passed". And, most astonishing of all, as The Independent on Sunday exclusively reported last week, President George W Bush is alarming the oily right by considering a U-turn on climate-change policy.

We have been waiting a long time for this. For almost the entire life of this newspaper we have been campaigning on global warming, reporting the alarming scientific findings, penetrating the smokescreen erected by the more unscrupulous oil companies and their acolytes, and nagging political leaders to take action, rather than just spout words. It has been a lonely business for much of the time, though it is good to see previously lagging newspapers now adding their voices. A particularly warm welcome, please, for the latest arrivals, The Sun and The Observer. True, some commentators, not unlike King Canute's courtiers, still deny that anything is wrong. But the real debate is over.

So now, as James Cameron argues on these pages, we must move to action - and fast. The prolonged debate has greatly reduced the time left in which to avert catastrophe. The first important opportunity comes with the next round of negotiations, in November, over what will succeed Kyoto when it runs out in 2012. The last meeting, in Montreal last December, achieved surprising progress when the US overplayed its hand, causing such an outraged response that it had to back down. And here is an important lesson. Whenever Mr Blair has cosied up to George W Bush, the "toxic Texan" has been inclined to dig in his heels: but whenever isolated he has had to budge. It is crucial that the pressure is kept up on the President, now that he is really feeling the heat.

David Miliband, Secretary of State for the Environment, will lead the British delegation to the negotiations, which will provide the first - crucial - test of whether he is big enough for the international stage. But an even bigger test of character looms for Gordon Brown, Chancellor and prime-minister apparent. Over the past 18 months he has been taking an increasing interest in the issue, spurred by his concern for the poor of the Third World and the realisation that the climate change will hit them hardest. And last week he did secure an important, if unpublicised, victory in persuading the governments attending the World Bank's annual meeting - against the entrenched opposition of the US - to back a new $20bn fund to finance clean energy in developing countries. This autumn he will publish the results of an important review of the economics of climate change.

We cannot, however, be sure how deep it goes. Mr Brown promised, before coming to power, that he would be the greenest-ever Chancellor, but - despite a few initiatives such as the Climate Change Levy on industry - he has disappointed. We are going to take some convincing that he would be adequately committed to effective action as prime minister. Maybe he will make a start in his party conference speech this week. A similar question can be asked of David Cameron. It is true that he did much - as Sir Richard would say - to kick-start the process by taking up the issue on being elected Conservative leader. It has certainly brought him great success, being the most important factor (apart from the disintegration of the Blair regime) in making his party a credible election prospect. But doubts must remain about how deeply his green priorities have penetrated into his party; an important test will be whether he can bring Tory MEPs into line over crucial EU legislation on controlling toxic chemicals this autumn.

Of course, in the end, beating global warming depends on us. All the political leadership in the world will make no difference if we go on recklessly wasting energy and emitting far too much greenhouse gas. But conversely, individual changes are unlikely to happen, or be effective enough, unless there is leadership that sets the rules, and taxes to encourage environmentally friendly behaviour. Both Gordon Brown and David Cameron urgently need to turn their attention to this. Only then will the promise of the past week have any chance of being realised.