I believe that you are looking at the picture incorrectly.
Let's try a mind experiment.
Let's assume that the world including the atmosphere is as it is today, with he sun switched off. Let's replace GHG with a half silvered mirror, transparent to shortwave, instead of the GHG absorption and radiation in all diirections that we know is the truth.
Switch on the sun.
The earth will start warming from the impinging solar energy. When will it stop warming? When the temperature of the surface is hot enough to radiate 396 W/M2 and therefore the net energy out = the energy captured from the sun.
Replace the half silvered mirror with one twice as reflective. What happens? The first thing would be that the net energy out would halve, the world would start warming, until it reaches a new temperature that once again restores the energy out balance with incoming energy.
How many years would that take, and what would be the final temperature?
For others to determine.
there are a few things that you seem to be confused about. solar input is the stable component of the temperature equilibrium, therefore the surface can be a wide range of temperatures depending on the conditions for heat loss. this is an important point! without GHGs to constrain IR radiation from directly escaping to space the surface would be ~minus 18C. the 496W/m2 from the surface is a combination of solar input and charged heat sinks of the ground and atmosphere. it can have many other values but the net output from the earth must equal the net input from the sun ( to a close degree, the conditions are always changing).
you are also confused about CO2 somehow being equivilent to a half-silvered mirror for IR radiation. it is not. the extinction length for CO2 reactive bands of IR is roughly 10 metres. got that? the IR is totally dispersed in random directions in 33 feet, it cannot become any less ordered. if a CO2 molecule has absorbed a suitable IR photon and is vibrating (quantum vibration, not ordinary vibration), then collides with another molecule, that IR quantum becomes part of the overall energy equation and can be emitted as blackbody radiation. if the CO2 molecule simply emits the same type of photon its direction has been randomized. because we dont care about the lateral component, only the vertical component, we say that half goes up and half goes down on avg. there is no 'reflection', only total dispersion, happening constantly.
while I admire your confidence in your ability to think things through, so do a lot of us here on the message board. I think you need to delve a little deeper because your posts have been very simplistic and in many cases have significant errors in them.
First, hopefully you realized that I understand the GHGs absorb and re-radiate, I was using the half silvered mirror as a metaphor. If you find it confusing, it's not a necessary part of the explanation.
From my perspective you are inclined to confuse things with frequency domain stuff that is both confusing and unnecessary. The only relevant commodity is energy, no matter it's form.
Also, you intoduced Trenbarth's energy budget, so I assumed that you bought into his portrayal of reality.
Considering the energy budget and simple physics, I don't see how anybody can, and certainly nobody has, come up with any rational that denies AGW.
GHGs make it harder, considering outgoing longwave radiation, to achieve energy balance. The force that overcomes that additional resistance is the long term average temperature of the earth and atmosphere. With the incoming solar energy the same, and a reduction of outgoing longwave energy, the earth components will warm. There simply is no other possibility to achieve eventual equilibrium.
The dynamics of the transition are very complex, made more so by the reality of daily massive additions to our atmospheric GHGs, but the stable end can only be achieved by a warmer planet and atmosphere.