Check this out. McCain and Obama respond to 14 questions presented by the scientific community on topics ranging from the health of the world's oceans to stem cell research to the climate to the looming water crisis.
I particularly recommend perusing the comments section where there is some political posturing but mostly some really informed responses to the candidates' answers. A few point out that McCain's stem cell answer confuses embryos and fetuses, for example, and his take on water is entirely locked up with his Western state POV.
Not surprisingly, I learned a few things from the discussion. "Virtual water," for example. It's the amount of water needed to produce something. The World Water Council states that it takes about 1,000 liters of water to produce a kilo of wheat.