Thank you for this post.
The effect of adding extra CO2 to the atmosphere is fundamental to explaining the temperature of the atmosphere and the earth.
While I disagree on the level of the feedbacks and other interactions the temperature increase due to CO2 increase causes it has an obvious effect*.
One of the problems I have is defining the surface of the planet as an effective entity.
Because of the atmosphere, which in a sense is part of the surface when it reflects light [That light bounced of earth] we do not have a real surface like a meteorite or the moon but a layer of surfaces depending on what depth the light penetrates too.
This leads to your concept of a radiating layer [then the layer from which the energy is radiated directly to space will move to a slightly higher altitude.], also known as a TOA, which is an artificial designation of the effective surface layer of the earth.
“Essentially, the presence of greenhouse gases prevents energy from being radiated directly from the surface to space; instead it’s radiated from within the atmosphere. you can think of there being a layer in the atmosphere where the energy can be radiated directly to space.” Yes.
“However, the temperature of the atmosphere decreases with increasing altitude, and so moving the radiating layer to a higher altitude will reduce the outgoing energy flux.”
Not happy with this comment as the outgoing energy flux total must be higher. The real temperature at the artificial TOA is not the same thing as the construct of “what temperature the TOA needs to be to radiate this amount of energy into space. Two problems.
The amount of energy going out to space from a square meter at that extra height means there are more meters for the energy to go out from. Which means there is an increased outgoing [total] energy flux. Which makes sense as the earth is hotter.
Technically if the earth is warmer then the temperature at the higher altitude now being used would be warmer than what it was before. Practically as it is an artificial construct the air is warmer at lower heights than it used to be and probably does not change in temperature at all. Being very thin and not much GHG or energy absorbent molecules at 100 km.
“If we were in energy balance before adding the extra CO2, then we’ll now have more energy coming in than going out, and we’ll warm until we’re back in energy balance.”
Conceptually the energy coming in balances the energy going out. The instance you put the CO2 extra in it increases the heat of the atmosphere it is in* by delaying the return of that heat as energy to space. This is a momentary and continuous delay the end effect is as you say, energy in equals energy out or energy balance..