There's this standard argument that so called 'climate skeptics' like to toss around.
There's so much water vapor in the atmosphere. Since water vapor is a more potent greenhouse gas, surely, the teeny weeny CO2 concentrations (only limited to ppms) can't trap all that radiation! Thus Al-gore is after my bank account.
I'd always assumed that the amount of water vapor was constant, and not growing - therefore it was not to be such a big deal. This is probably incorrect, since an increase in global temperatures will mean more evaporation, and therefore more water vapor at a given point of time. A positive feedback.
However, things, it seems are much more complicated. The atmosphere is so massive that it does not act like a single lumped layer. There's some radiation frequencies that the atmosphere fully absorbs (and starts re-radiating), there's some that go through unscathed.
Apparently, CO2 that's way high up, where no water vapor molecules dare to go. Also CO2 spectral transmittivity differs from that of water vapor. That's why increasing CO2 concentration increasing average global temperatures. This remarkable article from realcimate.org clarifies. I also found this page fun to peruse. Fairly wonkish, I will have to read this in more detail later.
So, I tell you why there's so many skeptics out there. The science is too tough to understand, so people would like to follow their gut. And the gut of the average American conservative is a pretty simple thing. It will follow the mantras of individual responsibility and small government. The American conservative does not think too much of 'ivory tower inhabiting liberal intellectuals'.