If a gas can emit radiation, and if a function of a gas such as so called greenhouse gases is to emit radiation, and that more so called greenhouse gases emit more radiation, then such a gas provides a mechanism for cooling...not warming. The ability to emit radiation is given by a factor called emissivity. If a surface or substance has low emissivity, then it has to attain a higher temperature to emit a given quantity of energy. by the same token, something with high emissivity will conversely have a lower temperature needed to emit a given quantity of energy. The relation between a surface's or substance's temperature is inversely proportional to its ability to radiatively emit energy i.e. its emissivity.
Thanks for actually making an attempt at explaining your position. It helps me see where you are coming from.
Emissivity is the ability of a substance to absorb/emit specific wavelengths of EMR. You cannot have the ability for one without the ability for the other. Obviously.
You mentioned that temperature has a relationship with emissivity. Indeed it does, while a substance can always absorb favoured bands of radiation it can only produce that radiation if there is enough available energy. And the higher the amount of available energy (AKA temperature), the larger the amount of radiation (
j=eaT^4).
Let's use CO2 as an example. The amount of radiation energy it absorbs and adds to the atmosphere is only limited by the amount of 15 micron radiation the surface produces. The cooling it is responsible for is limited by the amount of 15 micron radiation produced by the cold atmosphere at the emission height.
Ordinarily I would mention that some radiation energy would reurn to the surface but I don't want to leave the topic of emissivity.
CO2 has three bands in IR where the emissivity is one, unity. 15, 4, 3 microns. Why do we not talk about the bands at 4 and 3? Because the Sun sends very little of those to the Earth, and the Earth's surface is not warm enough to produce it.
Are there bands that CO2 has an emissivity of 0<x <1 ? Yes of course. Near the surface there are pressure effects that widen the 15 micron band to a 14-16 micron band. Like a badly fitting key, it only works if you hold it just right. That is why the CO2 notch gets wider at higher concentration but any escaping radition comes from a high temperature low altitude emission height.
All GHGs produce the same type of result. They absorb more surface emitted radiation than they eventually emit to space from a cold high altitude.
Increasing the amount of a specific GHG will increase the radiation absorbed near the surface and decrease the amount released to space.
Personally I think that the miniscule amount of increased emissivity near the surface (via widening the wings by pressure) should be ignored here as unnecessary complexity. It does not reduce the GreenhouseEffect, it adds to it.
So SSDD. I will ask you again, why do you think adding more GHGs will cool the atmosphere? What energy reservoir will it be depleting, and by which wavelengths?
