Back in May, Friends of the Earth endorsed Barack Obama. By August they were putting out statements attacking his decision to embrace a bill that would have allowed drilling in Alaska and slamming his support for 'dirty liquid coal'.

Such has been the pattern of this election. The environmental lobby get momentarily excited about the candidates on offer. Then someone asks a question about energy policy and their green credentials go out the window. Obama favours renewable energy targets, but is also a proud supporter of food-price boosting ethanol subsidies. John McCain says that tackling global warming will be one of the priorities of his presidency. Yet he wants to hand carbon permits to polluting industries, and has made a campaign slogan of 'drill baby drill'.

Americans are waking up to global warming. But cheap petrol and low taxes come first every time - and where voters lead, politicians will follow. "Most people want to do the right thing, but there's the big picture, and there's today," says Rich Bowden, a professor of environmental studies at Allegheny College, Pennsylvania. "If you ask if they care or would they spend money to protect the environment, they'll say yes. If you look at their actual behaviour you get a rather different answer."

Much of the nation's failure of will can be credited to its leaders' failure to actually lead. FDR called on the US to build 50,000 aeroplanes; JFK announced it would put a man on the moon before the decade was out. The best the environmental movement has found was Al Gore, and he lost.

Indeed, plenty of US politicians have done all they can to push the country in the other direction. George W. Bush has slashed environmental protections. Ronald Reagan cut funding for renewable energy, removed the solar panels from the White House, and appointed a secretary of the interior who believed it was okay to pillage the Earth because the Rapture
was coming.

Even Ted Kennedy drew pure green fury earlier this year when he tried to block a wind farm development off Cape Cod, for the marvellously patrician reason that it would ruin the view from his yacht.
("What right do people in Massachusetts have to do that?" fumes Bowden. "I live in a state where people are ripping the tops off mountains and pouring them into streams.")

This year's candidates are better - but only just. And the endorsements for Obama are as much a judgement against McCain as enthusiasm for the Democrat.

"It's a choice between 'drill baby drill' and change - but we don't know what that change will be," says Bowden. That's a worry. After all, environmental collapse is change too.