Via Tyler Cowen, here's a very nice three-part primer (1, 2, 3) at Effect Measure on the science of greenhouse gases—what they actually are, why they trap heat, why carbon-dioxide is a greenhouse gas but not, say, oxygen. This is really just the basic, basic physics and of course not the sum total of what's known about climate change (for that, the IPCC is the go-to guide), but it's still a handy reference in case you're curious. Though possibly it's no one else's idea of thrilling afternoon reading on a Sunday...