As I understand the original rationale behind the "greenhouse gas" hypothesis, CO2 "insulates" because it absorbs (and emits) light energy in a broad band in the infrared--IOW, it has a broad fluorescence band in the IR range. That is the basis of its "reflection" of infrared. The thing is, it absorbs IR energy from all directions, and reemits it in all directions. So there is no net quantity of IR energy being redirected back towards the earth, and thus no net increase in heat directed at the earth. Substances can increase the heat of the atmosphere, by absorbing the energy of visible light and reemitting it as IR light--but CO2 does not do that, since it is transparent within the visible range.
The only thing that anyone ever told me that could account for CO2 increasing the total heat energy content of the atmosphere is that within the fraction of a second where a CO2 molecule has absorbed IR light and not yet emitted it, the CO2 molecule could bump into another atmospheric molecule (e.g. N3 or O2) and transfer that extra energy to it. That would increase the kinetic energy of that molecule, which would manifest as heat.
Anyway, I hope I did not become hopelessly technical here.
OK, I see what you mean. Yes, that's true. But in the case of CO2 in the atmosphere it's an imbalance because the incoming energy from the sun heats the earth, which radiates infrared. There's more infrared coming from below than above.
"Anyway, I hope I did not become hopelessly technical here."
Don't worry, I do technical.