An Inconvenient Truth (2006)

"An Inconvenient Truth" is based partly on a presentation by Al Gore.

But when this does not happen — and it is hardly a partisan statement to observe that, in the case ofglobal warming, it hasn't — others must take up the responsibility: filmmakers, activists, scientists, even retired politicians. That "An Inconvenient Truth" should not have to exist is a reason to be grateful that it does.

Appearances to the contrary, Mr. Guggenheim's movie is not really about Al Gore. It consists mainly of a multimedia presentation on climate change that Mr. Gore has given many times over the last few years, interspersed with interviews and Mr. Gore's voice-over reflections on his life in and out of politics. His presence is, in some ways, a distraction, since it guarantees that "An Inconvenient Truth" will become fodder for the cynical, ideologically facile sniping that often passes for political discourse these days. But really, the idea that worrying about the effect of carbon-dioxide emissions on the world's climate makes you some kind of liberal kook is as tired as the image of Mr. Gore as a stiff, humorless speaker, someone to make fun of rather than take seriously.

In any case, Mr. Gore has long since proven to be a deft self-satirist. (He recently told a moderator at a Cannes Film Festival news conference to address him as "your Adequacy.") He makes a few jokes to leaven the grim gist of "An Inconvenient Truth," and some of them are funny, in the style of a college lecturer's attempts to keep the attention of his captive audience. Indeed, his onstage manner — pacing back and forth, fiddling with gadgets, gesturing for emphasis — is more a professor's than a politician's. If he were not the man who, in his own formulation "used to be the next president of the United States of America," he might have settled down to tenure and a Volvo (or maybe a Prius) in some leafy academic grove.

But as I said, the movie is not about him. He is, rather, the surprisingly engaging vehicle for some very disturbing information. His explanations of complex environmental phenomena — the jet stream has always been a particularly tough one for me to grasp — are clear, and while some of the visual aids are a little corny, most of the images are stark, illuminating and powerful.

I can't think of another movie in which the display of a graph elicited gasps of horror, but when the red lines showing the increasing rates of carbon-dioxide emissions and the corresponding rise in temperatures come on screen, the effect is jolting and chilling. Photographs of receding ice fields and glaciers — consequences of climate change that have already taken place — are as disturbing as speculative maps of submerged coastlines. The news of increased hurricane activity and warming oceans is all the more alarming for being delivered in Mr. Gore's matter-of-fact, scholarly tone.

He speaks of the need to reduce carbon-dioxide emissions as a "moral imperative," and most people who see this movie will do so out of a sense of duty, which seems to me entirely appropriate. Luckily, it happens to be a well-made documentary, edited crisply enough to keep it from feeling like 90 minutes of C-Span and shaped to give Mr. Gore's argument a real sense of drama. As unsettling as it can be, it is also intellectually exhilarating, and, like any good piece of pedagogy, whets the appetite for further study. This is not everything you need to know about global warming: that's the point. But it is a good place to start, and to continue, a process of education that could hardly be more urgent. "An Inconvenient Truth" is a necessary film.

"An Inconvenient Truth" is rated PG (Parental guidance suggested). Some of the subjects discussed might be upsetting.

An Inconvenient Truth

Opens today in New York and Los Angeles.

Directed by Davis Guggenheim; produced by Laurie David, Lawrence Bender and Scott Z. Burns; released by Paramount Classics and Participant Productions. Running time: 96 minutes.