Let's have another look at what Roy Spencer writes about the GGH:
6) The tropospheric temperature lapse rate would not exist without the greenhouse effect. While it is true that convective overturning of the atmosphere leads to the observed lapse rate, that convection itself would not exist without the greenhouse effect constantly destabilizing the lapse rate through warming the lower atmosphere and cooling the upper atmosphere. Without the destabilization provided by the greenhouse effect, convective overturning would slow and quite possible cease altogether. The atmosphere would eventually become isothermal, as the full depth of the atmosphere would achieve the same temperature as the surface through thermal conduction; without IR emission, the middle and upper troposphere would have no way to cool itself in the face of this heating. This scenario is entirely theoretical, though, and depends upon the atmosphere absorbing/emitting absolutely no IR energy, which does not happen in the real world.
The first thing worth to say about this is that it is a correct account of the GGH. For some reason skeptics have had a tremendously hard time to understand the significance of this. The lukewarmers have been very anxious to keep this secret for understandable reasons. Why? Elementary, because it provides a test which could potentially lead to a falsification of the theory.
Expressed in other terms, what he says is that if the atmosphere was depleted of greenhouse gases the tropopause would be at the surface. Remember, the tropopause marks the beginning of the stratosphere which is the isothermal layer above the troposphere.
Now please have a look at the following fact sheet:
Almost consistently, we see that the tropopause is situated at a pressure of about or slightly above 100 mB. (Mars beeing a notable exception, on the other hand it has a very thin atmosphere so the data might not be that reliable).
What does this mean. Well, the pressure is a direct measure of the amount of atmospheric mass above that level. Hence, it corroborates the assumption that it is the total mass, rather than the amount of GHGs that determine the amount of heat trapping in the atmosphere.