When you look at the logarithmic nature of CO2’s absorption of IR and keep in mind the ppm currently in the atmosphere, you can see that increasing levels of CO2 has less and less absorption potential. The reason is that, once the band of IR susceptible to absorption by CO2 has been absorbed, the addition of more CO2 cannot have any effect. This is proven in the laboratory. CO2 absorbs certain bands of the IR spectrum. Once these bands have been absorbed, CO2 is inert to the rest of the spectrum. Furthermore, the band of IR most susceptible to absorption by CO2 is entirely overlapped by H2O’s absorption spectrum, meaning that H2O is MUCH more capable of absorbing this band of IR and other bands. I hope this helps.
