In An Inconvenient Truth, perhaps the world's first film based on a PowerPoint presentation, Al Gore plays himself: a sometimes brooding, sometimes funny ex-politician come to deliver a message about "a planetary emergency". He gives an impressive performance, one that the American press - a group that never before seemed terribly sympathetic to the former vice-president - has greeted with almost universal enthusiasm. (In two fairly representative examples: the New York Times described Gore as "the surprisingly engaging vehicle for some very disturbing information", while USA Today called the documentary a showcase for his "dedica-tion, warmth and, yes, charm".) An Inconvenient Truth has prompted a great deal of discussion in the United States about what might have happened had Gore revealed a few more of the qualities of his on-screen persona while out campaigning in 2000, and even more speculation about whether he is preparing to run again in 2008.
Perhaps not surprisingly, the strongest claims about the film's reception have come from the star himself. Speaking last month on the popular public radio show Fresh Air, Gore said that recent events had made him "optimistic" that American attitudes towards global warming were finally changing. The US political system, he further observed, "shares one thing in common with the climate system. It's non-linear. It can appear to move at a glacier's pace and then, after crossing a tipping point, it can suddenly move rapidly into a completely new pattern. I've seen that happen."
Certainly, there are few questions more urgent than how - and how quickly - the US will react to climate change. As is well known, Americans represent less than 5 per cent of the world's population, and yet they produce roughly 25 per cent of its carbon-dioxide emissions. The country is one of only two industrialised nations that has rejected the Kyoto Protocol and, with it, mandatory emissions cuts. (The other is Australia.) Even as European leaders are pushing for negotiations to begin on a post-Kyoto treaty, the US has refused to participate. And on and on. At this point, it is almost impossible to imagine how the world will avoid disastrous climate impacts without a fundamental, and prompt, change in US policy.
Gore's professed optimism that such a change is at hand, which is shared, at least for the purposes of public consumption, by many of the country's leading environmentalists, rests on what might be called the democratic (with a small "d") imperative. As Gore points out, accurately enough, companies such as ExxonMobil and General Motors, working in concert with right-wing think-tanks such as the George C Marshall Institute, have spent millions of dollars trying systematically to obscure the facts. (Indeed, as if on cue, the Competitive Enterprise Institute greeted the première of Gore's movie with a pair of 60-second TV ads full of jumping gazelles and kids skipping rope, carrying the tag line: "Carbon dioxide: they call it pollution; we call it life.") Add to this an American press corps axiomatically devoted to the notion of "balance", and the result has been confusion. But as soon as Americans understand "the inconvenient truth" about climate change, Gore has asserted, they'll do the right thing.
Making generalisations about an entire nation is always a dubious enterprise, and this is especially true of the US. The modern environmental movement was born in America and enjoyed its first successes there. Even under George W Bush - perhaps the most polluter-friendly president in the nation's history - the country still spends more money than any other on environmental science; as the president likes to boast, this year alone, the federal government will spend roughly $2bn on climate research and monitoring. Britain's Met Office has the Hadley Centre: the US supports three climate modelling teams - one at Nasa, the second at the National Oceanic and Atmospheric Administration (NOAA) and the third at the National Centre for Atmospheric Research (NCAR).
All around the country there are towns and cities and state governments that are actively working to reduce their emissions in spite of - or perhaps one should say because of - federal inaction. In February 2005 the mayor of Seattle, Greg Nickels, began to circulate the "US Mayors Climate Protection Agreement", which calls on cities to " strive to meet or beat the Kyoto Protocol targets in their own communities"; as of this month, 243 mayors, representing communities as diverse as Miami, Racine in Wisconsin and Charleston, South Carolina, had signed on. New York, New Jersey and several other north-eastern states have pledged to freeze their power-plant emissions at current levels and, eventually, to begin to roll them back. Even Governor Arnold Schwarzenegger, the Hummer collector, has joined in the effort: an executive order he signed last year calls on Califor-nia to reduce its greenhouse-gas emissions to 2000 levels by 2010 and to 1990 levels by 2020. "I say the debate is over," Schwarzenegger declared before signing the order. "We know the science. We see the threat. And we know the time for action is now." The California Public Utilities Commission recently launched a $2.9bn rebate programme aimed at installing solar-power arrays on one million rooftops.
Ballooning house sizes If you focus on efforts such as these, it's tempting to conclude that the US is ready to shift course and, indeed, to some extent is already doing so. Look elsewhere, however, and it's far less clear. Consider what has happened to the average new home built in the country. Even as average household size has declined, the size of the average house has ballooned. It was 1,000 square feet in 1950 and is nearly 2,500 square feet to-day. New homes, meanwhile, now routinely feature a gamut of energy-intensive conveniences, such as outdoor kitchens, professional-sized appliances and heated towel racks.
Or consider what has happened to the American automobile. At the same time Americans were being presented with ever more compelling evidence of global climate change, they were also, in ever greater numbers, purchasing cars like GM's Yukon Denali, which has a 335-horsepower engine, weighs 7,000lb, comes equipped with heated leather seats, and gets 13 miles to the gallon. On average, passenger vehicles purchased in the US last year got 21.0 miles to the gallon; this was a worse gas mileage than the average passenger vehicle got 20 years earlier. In many parts of the country George Bush's recalcitrance isn't representative, but in others his equivo-cations look positively progressive: Senator James Inhofe, Republican of Oklahoma, who chairs the Senate committee on environment and public works, has famously called global warming the "greatest hoax ever perpetrated on the American people". Every year Senator John McCain, the Republican Party's most vocal proponent of action on climate change, brings to the floor a bill that would impose federal limits on CO2 emissions. Every year it's a foregone conclusion that the bill will be defeated. It is worth noting that all the way back in 1992, Gore published a book, Earth in the Balance, which eloquently laid out the dangers of global warming. The book became a bestseller. Gore became the vice-president. And still nothing happened.
Are such patterns really the result of disinformation? Do Americans drive around in 7,000lb cars because somehow they missed the many thousands of news stories and scientific studies documenting record high temperatures, rising sea levels and shrinking ice caps? As an American, I'd like to believe this is so. But it's hard to.
Life in the United States, more than just about anywhere else save perhaps some of the oil-producing Gulf states, depends on cheap and plentiful energy. This is a fact of American culture and also of the American economy. Really addressing the problem of climate change will require many small-scale adjustments (no more heated towel racks) and also a great many more substantial ones: changes in energy consumption, energy production, patterns of land use, transportation systems, international relations. Rather than assume that Americans haven't done anything about global warming because they are sceptical about the threat, one could just as plausibly argue that they are sceptical about the threat because they don't want to do anything.
Shortly after Gore was elected vice-president, he proposed a tax on energy - specifically on the energy content of fossil fuels. It was defeated ignominiously, even though the Demo-crats still controlled Congress. Gore never raised the prospect of an energy tax again. Four years later he flew to Japan to salvage the Kyoto Protocol when negotiations seemed on the verge of breaking down. The Clinton administration eventually signed the protocol but never presented it to the Senate for ratification. Though Gore knew that the very future of the planet was at stake, he apparently concluded that pressing for action was hopeless, or politically inexpedient, or both. Talk about an inconvenient truth.
Beyond the tipping point
At this point, midterm elections in the US are just five months away. Recent polls suggest that control of both houses of Congress is up for grabs. It's possible that the Democrats will win a majority in at least one, in which case the chairmanships of certain important committees will shift to less openly anti-science members. On the other hand, it is also possible that the Republicans will retain their majorities, in which case they are likely to interpret the results as a mandate for staying the course. Two years from now is a presidential election. Among the current leading contenders are some of the most passionate advocates of action - Gore and McCain - and also some of the leading obstructionists, such as Senator Chuck Hagel, Republican of Nebraska. (Hagel was among the chief opponents of Kyoto.) Whoever wins in 2008 will face an American public that still expects the government to respond to rising energy prices by cutting gasoline taxes.
Such is the inexorable nature of global warming that, at some point or other, even the US will be forced to acknowledge the scale of the problem. As McCain has observed: "This is clearly an issue that we will win on over time because of the evidence." The tragedy is: we don't have more time. The earth's climate system is vast and hugely inertial, and so already we are much further along the path to catastrophe than it appears. The rapid melting of mountain glaciers, the accelerating flow off the Greenland ice sheet, the 2003 heatwave in Europe, the 2005 hurricane season in the US - these are just the first faint harbingers of changes that have, by now, already become inevitable.
If we continue on our present course, at a certain point, truly terrible climatic disasters - the disintegration of the Greenland or the West Antarctic ice sheet, for instance - will become similarly unavoidable. These disasters may take centuries to play out fully, but once the process begins, it will become self-reinforcing and therefore virtually impossible to stop. This "tipping point" could be reached 20 years from now, or ten years from now, or, if truth be told, it could have already been reached ten years ago. Of course the US can go green. The question is: will it do so before it is too late?
Elizabeth Kolbert is a writer for the New Yorker. Her book "Field Notes from a Catastrophe: climate change - is time running out?" is published by Bloomsbury (£14.99)
The changemakers? A who's who of US greens
by Nicholas Wapshott
Barbra Streisand Between railing against Bush and the Iraq war on her website, the Democratic diva champions green issues and declared this month that she would go back on tour after a 12-year absence to raise money for her charity, which backs environmental causes.
Al Gore The green veep who "lost" the presidency by a whisker has remade himself as America's favourite green. The author of Earth in the Balance, published in 1992, took his autobiographical climate-change multimedia roadshow on tour, filmed as the must-see documentary An Inconvenient Truth.
Senator John McCain The green mostly likely to inhabit the White House, the Republican senator from Arizona, former Vietnam prisoner-of-war and presidential front-runner defies and offends fellow conservatives by unequivocally blaming global warming on human beings and backing measures to reduce greenhouse gases.
George Pataki The governor of New York, whose hero is the first environmentalist president, Theodore Roosevelt, upset fellow Republicans by setting strict limits for greenhouse gases. Has persuaded industry to set aside 750,000 acres of unspoiled upstate forest and wetlands.
Hank Paulson When he was boss of Goldman Sachs, George W Bush's new secretary of the treasury, a keen twitcher and chairman of the Nature Conservancy, set greenhouse-gas limits on the firm's properties, invested $1bn in renewable energy, and set aside 680,000 acres of peatbog and forest in Tierra del Fuego.
Laurie David Wife of the Seinfeld creator, Larry David, she produced Gore's An Inconvenient Truth (see above). She campaigns through her eponymous website as well as through www.stopglobalwarming.org. She also blogs on the Huffington Post and the virtual protest marches and write-ins to America's mayors. Producer of this year's hot green documentary Too Hot Not to Handle.
Robert F Kennedy, Jr Son of Bobby Kennedy, he is professor of environmental law at Pace University, New York, leading the fight against polluters of America's waterways through Riverkeeper, which keeps the Hudson clean, and its worldwide equivalent, Waterkeeper Alliance. Hosts weekly green radio show on Air America.
Douglas Durst The New York construction and real-estate magnate's motto is, "People who aren't building green buildings are building obsolete buildings." And he has been as good as his word, championing the erection of energy-self-sufficient office towers in Manhattan.
Arnold Schwarzenegger The Terminator who turned Republican governor of California in 2003 shocked his own party last year by issuing an executive order to reduce the state's greenhouse gases by a quarter by 2020. The first owner of a civilian Hummer, he converted it to burning hydrogen and instigated the California Hydrogen Highway Network.
America's green record
5.8 billion Metric tons of CO2 produced by the United States each year
25% Proportion of global CO2 emissions produced by the US
32% US households with three or more cars
80% Increase in US road travel over the past two decades
53 Number of days after Bush took office that he reneged on his campaign promise to regulate CO2 emissions
1 Number in Bush's 63-person energy advisory team of 2001 with no ties to corporate energy interests