Are US politicians suddenly so convinced of the threat of global warming that they are prepared to do something about it?

No: probably not for years, for all the talk. President Bush’s decision to refer to climate change and energy security in his State of the Union address last night shows that it is on the political map; so, more emphatically, do the congressional measures on the theme.

That doesn’t mean that the White House or Congress is prepared to rush into action — nor should they be. Some of the reluctance stems from well-founded concern about economic growth, given the formidable size of the required changes.

For a president’s scriptwriters, the State of the Union speech is a challenge of balance that it is almost impossible to get right: too domestic, and the president appears parochial; too foreign, and he appears evasive and irrelevant. Bush’s dilemma about whether to stir the planet’s atmosphere into that lumpy mixture was comical.

After five years of war, climate change offers a welcome distraction — except that it is not a battle that is going to make any president look good. For all Al Gore’s success with his film An Inconvenient Truth, it is not a subject that flatters politicians: it is technical, threatening and its consequences potentially overwhelming for some communities — but impossible to predict. It flatters the more impersonal politicians, like Gore; David Cameron struggled to warm it up with huskies and polar bears.

The White House has stretched itself to accommodate the new mood by stapling climate change to the theme of energy security. It has been pushed into that position by the chiding of other leaders, notably Tony Blair and Angela Merkel, the German Chancellor — and by the conviction of the new Democratic- controlled Congress that this theme has great potential.

In the past fortnight Congress has poured out eight Bills proposing to limit emissions, and more may come. Polls show that fear of global warming has shot up the list of public concerns.

Yet when the same polls ask whether people want to pay more to do something about it, they generally answer no — and particularly loudly in the poorer communities that are the Democratic bedrock.

Rising petrol prices have made Americans alert to their vulnerability, but no more willing to pay up. Nor does any politician want to risk higher fuel taxes, even if far below the levels in Europe. So they take refuge in plans to raise the fuel efficiency standards on new cars, among the lowest in the world.

Those would take years to show an effect. So would investment in making coal-fired power stations cleaner. Yet that innovation could prove one of the most environmentally valuable exports, to China, for instance. This slow change, frustrating to activists, may be what the US can best deliver.

The US, in its objections to the Kyoto Protocol that have earned it such opprobrium in Europe, made fair points about the dependency of its economy on cheap transport and certain kinds of energy. It could not redraw those features as quickly as could Europe, with the “advantage” of jettisoning crumbling, dirty old industries.

The benefits of US economic growth for other countries are clear. It is not ducking the issue to argue that in the interests of protecting that growth, it will change, but slowly.

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