You missed my point. The operative word there is *alone*. Concentration is absolutely an important variable, but only when considered in conjunction with the properties of the molecule in question. Add huge amounts of a gas that doesn't absorb radiation and you'll have very little effect on temperature. Add relatively small amounts of a gas that absorbs strongly at a relevant wavelength and you *will* have an effect - and that effect will, of course, be concentration dependent. Add more, and you'll have a larger effect.
