I was surprised to see two skeptic blogs describe the "Greenhouse Effect" in their first post of the new year. Dr. Roy Spencer started it with Misunderstood Basic Concepts and the Greenhouse Effect which was commented on by Lubos Motl Greenhouse Effect doesn't contradict any laws of physics.
One of the misunderstood concepts is that sunlight is required for the greenhouse effect. That is true. The "Greenhouse Effect" doesn't depend on the source of the heat, just that there is heat and the atmosphere is a barrier to that heat loss.
My add to this would be that the more uniform the source of the heat the more efficient the "greenhouse effect" would be.
Think about a round room versus a square room. If you place a single source in the center of each room, the round room would be more uniformly heated than the square room simply because of the geometry. If you placed the heat source against a wall in either, the round room would still be more uniformly heated. Since the square room would have corners, if you placed the heat source in a corner, that would be the most inefficient location to place the heat source. If the insulation is very good, location would matter less.
To determine the temperature at a given place both the incoming and outgoing energy must be considered. Also true.
Consider the round and square rooms, if one section of either has less insulation value and the heat source is closer to the less well insulated section, the temperature of both rooms would be different than is they where equally well insulated.
Both points agree with the second law of thermodynamics. Of course.
Infrared adsorption and infrared emission are almost always different from each other for a given radiant layer. Without a doubt, an ideal radiant surface is an idealized construct, a useful tool, nothing more. The thinkness of a radiant surface would have to be "tuned" to the perfect optical depth for each frequency range to approach "ideal" and there could be no convection, advection or scattering meaning both the volume above and below the radiant layer would have to be isothermal. As a tool, it is only useful if you remember its limitations.
Radiation going up and radiation going down from a radiant layer aren't equal either. Because of the last condition this has to be true.
The existence of the lapse rate itself requires the "Greenhouse Effect". Of course, an ideal black body and and ideal grey body do not exist, but they are useful "models" to compare to reality.
All these are pretty much points I have made in the past. In fact, my personal estimate of the impact of a doubling of CO2 is lower than the "no feedback" sensitivity because it would required near "ideal" conditions to produce the full impact of that estimate of sensitivity. There is always some degree of inefficiency that bites ya in the butt, based on Murphy's Law.
The first two point I used a simple comparison of two rooms. If you consider that the "walls" of the rooms are moist air, you would understand more of the points I have attempted to make. Now that the material of the wall construction is known, what is the shape of the "room" and where is the heat source placed? Figure that out and you can use any dry radiant layer to finish solving the problem, if you can get the room to stop spinning.