I've been attending, or at least surfing, David Archer's Coursera Global Warming class. It's probably not for the totally innocent, but a good high school level background in chem or physics should let people understand most stuff. It's pretty good, though it took me a bit to get used to his style.
Some people I know who think they know a lot could learn a lot from it.
Of course those are mostly the people think they know everything.