Just a visual on way there is no back radiation at the surface.There is no "back radiation" warming the surface—that is a misconception.
At standard temperature and pressure (STP), CO2 can theoretically absorb up to 12 W/m² in its IR absorption band—if no water vapor is present.
However, since water vapor is far more abundant and has overlapping absorption bands, it absorbs the majority of that energy.
Once this IR energy is absorbed, it is immediately redistributed through molecular collisions to N2, O2, and other surrounding molecules (Collisional De-Excitation, CDE).This is the key point:
CO2 and H2O have virtually no capacity to radiate energy in most of the troposphere because the continuous collisions prevent radiative decay from occurring before the energy is transferred kinetically.Only at higher altitudes, where air density is lower and collisions are less frequent, can CO2 and H2O finally radiate energy away.
