There's no real scientific debate as to whether or not global warming is happening (at least in academic and research circles)... the debate itself is to what's causing it... man-made vs. a natural cycle.
The thing that gets me about the naysayers though, is that even if our insane CO2 emissions aren't causing it to happen, it's hard to argue that it just isn't good for us.
When you consider the tons of emissions we let out (not just CO2), you have to wonder "what is this shit doing to us?" I mean, we wouldn't stick our faces onto a car exhaust and breathe it because it would kill us within minutes... but when you multiply that by millions, then include every factory with smoke stacks, you can't help but realize that we're turning the planet into a big noxious marble.
If we keep it up, we'll wind up like Venus.