It seems that Spencer, WUWT, Lubos and of course all climate alarmists, take the existence of a GHGE for granted, maybe because it has an acronym, while the nature of this effect remains elusive, which makes serious scientific discussion difficult or even meaningless.
Spencer gives the hint that GHGE "is an infrared effect" which connects to the common (mis)conception that the GHGE is an effect of radiation, more precisely, that the lapse rate, or temperature drop with atmospheric altitude, is determined by radiation.
- - alpha x dT/dx = Q
If the coefficient of heat conduction in still air is small, which is the case, then a small heat source at the bottom will prior to convective overturning establish a lapse rate equal to the dry adiabatic lapse in accordance with Loschmidt, a lapse rate thus determined by thermodynamics and not radiation.
To sum up: Loschmidt was more correct in the setting of the Earth atmosphere, since the Earth surface is heated, and the lapse rate is thus determined by thermodynamics and not by radiation. A GHGE based on a lapse rate determined by radiation, is just an acronym and no a real effect.
With the lapse rate determined by thermodynamics and not radiation, the role of GHG is limited to an effect on the temperature at the tropopause, which may not easily be changed by small perturbations in the radiative properties of the atmosphere, thus suggesting small climate sensitivity as discussed in previous posts.