It does not exactly have blockbuster written all over it. The film is a documentary about Al Gore, the famously wooden vice-president and failed presidential candidate, wheeling his suitcases from town to town and presenting a slideshow about climate change.

Former vice president Al Gore and director Davis Guggenheim at the Sundance film festival. Photograph: Mark Mainz/Getty

Yet An Inconvenient Truth is getting standing ovations at the Sundance film festival in Utah this week. The festival guide describes the film as a "gripping story" with "a visually mesmerising presentation" that is "activist cinema at its very best". In Nashville, Mr Gore's home town, fire marshals had to turn away hundreds of fans trying to get into a screening.

The film's unlikely success may have something to do with the producer, Lawrence Bender, who also made Pulp Fiction. But it is hard to imagine two more different films.

An Inconvenient Truth follows Mr Gore as he undergoes the daily indignities of emptying his pockets and taking off his shoes at airport security screens, sitting alone in hotel rooms working on his computer, and warning audiences around the world about the imminent danger of global warming.

Unlike his former boss, Bill Clinton, who is making millions on the lecture circuit, Mr Gore tells his story for free. In the film, he comes across as funnier and more self-deprecating than the stiff performer of the ill-fated 2000 presidential campaign.

He reveals that his commitment to the environmental cause was, in part, triggered by the near death of his son in a car accident in 1989, which he says forced him to ask: "How should I spend my time on this earth?"

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