The only suggestion I have as of now is Al Gore's An Inconvenient Truth, and I'm concerned that might be boring (though I've watched only about a minute of it so can't say). I thought of A Mighty Heart, though it's not strictly speaking, educational. But I want something that will hold their attention as well as prompt them to think about (and discuss) particular issues.
What do you suggest? Please help, readers! I need it for Sunday and the clock is ticking away.
Edited to add: Thanks, people. Due to a combination of circumstances (the group that had been planning to take a workshop but then tentatively cancelled have now confirmed, and I will be busy with something else that came up suddenly), we won't be having the movie screening this Sunday. But I'll keep these in mind for later, and do keep coming back and putting in suggestions (or send me an email).