We have been using a DVD at work called an Inconvenient Truth. It is a presentation by Al Gore (ex American Vice President) about global warming. We have based a number of sessions around the issues raised. I would recommend watching, (there is a fair bit of American sugar and slop) but it has a good message (and a bit scary). Al Gore comes across as a good man (he was almost the president instead of George W. Bush!)
There is also the web site well worth a visit.
Turn of those water taps, televisions and lights!!!