I believe the spectrums of IR absorbed by CO2 are already fully saturated, so that there is very little effect, if any, of increased CO2 levels in the atmosphere.
You're right, I misremembered. The 2-3x warming effect is due to other atmospheric effects ("radiative forcing") and nor direct effects of the emitted co2.
End result is the same however - the same fossil fuel is much worse when used in air travel than on the ground.
