Oxford University, in collaboration with ClimatePrediction.net, has created a "Climate Basics" website using interactive Flash to explain how climate change is predicted, for non-scientific audiences. The site's emphasis is very much on how we figure out what's coming, not explanations of greenhouse gases or why we know warming is happening, etc.; it's an interesting example of what a "global warming for beginners" looks like in a setting where the core evidence is already accepted and non-controversial.
I should emphasize that it is a very basic presentation, and several of the observers on RealClimate have pointed out some underlying problems with the probability math used in the program. The errors aren't anything that would change one's understanding of the issues, but more mathematically adept readers may wish to watch for them.
Hmmm... unfortunately, the "bucket" exercise featured in this creates more confusion than clarity. For a great stock and flow "bathtub" illustration that explains the problem better, see John Sterman and Linda Booth Sweeney's "why waiting won't do" article.
The "bucket" exercise is inaccurate in a couple of ways:
1) the "tap" is adjustable, but represents energy in from the sun (non-adjustable)
2) GHG emissions are represented by their impact - how much they trap energy in the earth's atmosphere - rather than as something that accumulates in the atmosphere.
3) carbon emissions are not adjustable (you can't alter the flow out of the bucket -- a much more plausible leverage point than turning the "tap" of solar energy on or off).
4) Unlike Sterman & Booth Sweeney's bathtub diagram, this doesn't express the dynamic between an increase in GCG emissions and the earth's ability to absorb emissions. It's that imbalance that causes the bathtub (or "stock", in systems thinking terms) to overflow, as GHG emissions annually exceed the earth's ability to absorb them.
As anyone who watched last nights' TBS special "Earth to America" (a comedy special to draw attention to global warming) can attest, it's hard to make the science clear and understandable (let alone funny) while retaining a level of accuracy. The bucket exercise doesn't quite get it right.