An Inconvenient Truth can't, of course, reveal a future that is still up to us, but by the time you're done watching, the real question is, Which way on God's green earth would you want to err?

Haunting and inspiring film.

Quite apart from its environmental agenda, the film is a reminder that there's no space for substance in political discourse: A 30-second soundbite on global warming could easily be brushed off as tree-hugging rhetoric, but after 100 minutes of level-headed elaboration, it's chillingly undeniable.

Gore looks as energized and purposeful as Mother Earth looks sickly and mad as hell, which is no doubt why many commentators suggested it was less an environmental action statement than a test balloon for future political ambitions.

As unsettling as it can be, it is also intellectually exhilarating, and, like any good piece of pedagogy, whets the appetite for further study.