THE MOST shocking sequence in An Inconvenient Truth is the ending. Former Vice President Al Gore doffs his clothes to reveal a makeshift caveman outfit. As the ushers pass sharpened spears to those assembled, all take a pledge to never use fossil fuels for cooking ever again. They further promise to abjure furnaces of any kind, in favor of huddling for warmth and hoping that the glow of politically correct superiority will be enough to keep their homes warm.

Well! It's not yet six years after Gore's anti-technology policies were soundly defeated by a little less than half of the voting public (not counting a few Floridians outwitted by ballots an origami master couldn't have unfolded) and here he is again filling impressionable brains with hoo-ha about melting ice caps and stuff that might happen 50 years from now.

By that time, as anti-global warming theorist Dr. Robert Balling Jr. told Business Week in 2004, "There will be engineering schemes that will allow our children's children to have whatever climate they want." After all, the new X-Men pic forecasts a race of homo superiors with the ability to quell storms by staring at them. Who is Al Gore to say this couldn't happen in real life? I, for one, welcome our mutant masters. Wringing the audience's heart with schmaltzy satellite photos of Earth is just one more way Gore deigns to promote the interests of the globe instead of the small North American quadrant of the planet that really matters. And most unforgivably, Gore uses humor in the lecture.

An Inconvenient Truth is a record of Gore's "traveling global-warming show." Those who have claimed that Gore would have made a first-rate professor now have proof. He excels at explaining the poetry of the biosphere, gulf-stream patterns and the seasonal adjustment of temperatures ("It's as if the Earth breathes in and out"). In a deservedly serious tone but in a monologue leavened with hope, Gore overcomes any moviegoer's natural resistance to lectures by use of multimedia props. He deploys PowerPoint graphics, anecdotes, a hydraulic lift and even a snippet from the global-warming episode of Futurama in which Gore appeared.

Director Davis Guggenheim includes scenes of Gore's private life, filming at a drowsy riverside in Tennessee near where Gore lives and including scenes of the former vice president addressing audiences about global warming. As an environmentalist, Gore was ahead of his time. Now, Hurricane Katrina got the nation's attention but that storm was just a small part of a pattern: the floods in Mumbai, the heat waves in Sydney and Europe, the drying up of the Aral Sea—all pieces of evidence of disaster to come, which can't be wished away by citing the Little Ice Age. (Gore mentions, and dismisses, that matter so close to the heart of those who believe global warming is a hoax.)

More evidence is set forth here: the calving of ice flows, the Antarctic core samples proving that CO2 gasses haven't been this high in eons, the reminder that 10 of the last 14 years have been the hottest on record. And as gas prices climb, along with the death tolls in Iraq, the necessity of overconsuming oil to keep the economy on track seems as outdated as the slogan "What's good for General Motors is good for the USA."

One point the film makes is the unusually high gas consumption of American cars. While some Americans would love to blame global warming on China's coal and gas consumption (let those heathen devils clean up their act first!), part of GM's financial woes derives from not being able to sell hulking cars to countries that have strict emissions standards. As Gore points out, one of these countries is China.

The film is less compelling away from the podium, which is another way of saying that Gore's climactic dog-and-pony show is more riveting than could be imagined. Guggenheim reiterates the turning points in Gore's life. One of these is the death of his sister Nancy from lung cancer, which taught Gore, a son of tobacco farmers, about the responsibility industry has to address the aftereffects of its products. And the lost election in 2000 is touched on: "That was a hard blow, but what can you do?"

Sometimes, the approach is aggressively lowball. The animated polar bears look like the white bruins that advertise Coca-Cola. The famous frog in the slowly boiling water seems to be an extra from Hoodwinked. I respect Gore's refusal to stand on false dignity, and obviously he needed to sweeten the medicine, but it can be rather sweet.

Still, Gore's quote from Churchill—"We are entering a period of consequences"—seems all the less arguable when compared with the kinds of sacrifices Gore is asking for. He's not flaunting the end-of-the-world, back-to-the caves policies I was mocking a few paragraphs up. Rather, he's insisting on conservation and new technology that won't make anyone seriously uncomfortable.

Gore's conclusions may even be too mild. Is he too optimistic? Will the public prefer to go, as Gore puts it, "straight from denial to despair"? This seminar of Gore's is fascinating enough that it may even make a difference. The good news is that he seems to believe it's not too late.

An Inconvenient Truth (PG; 96 min.), a film by Davis Guggenheim, opens June 2.

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