This post contains excerpts from "Principles of Modern Chemistry, 7th Edition" and will be a reference text for comments here and elsewhere regarding the physics and physical chemistry of the atmosphere, the gravito-thermal greenhouse effect, the laws of thermodynamics, entropy, enthalpy, and other related topics.
First up, a common misconception in the climate debate is that radiation from a cold body (e.g. the -18C atmosphere) can warm a hot body (e.g. the +15C Earth surface) just because the cold body does indeed send very-low-energy photons to the hot body. Heat transfer (not radiation) from cold to hot is forbidden by the 2nd Law of Thermodynamics on a macro basis, and by the Pauli Exclusion Principle of fundamental quantum theory on an atomic and molecular basis.
If a lower-quantum-energy photon is "absorbed" by the completely saturated low-energy microstates (eg vibrational, translational, rotational, chemical bonds) & molecular or atomic orbitals of a higher-energy body, the hot body must simultaneously eject a photon of the exact same wavelength/frequency/energy as that absorbed, due to the Pauli Exclusion Principle of fundamental quantum theory. Thus there is no change whatsoever in the energy content/temperature of the hotter body due to "absorbing" a low-energy photon from the colder source with simultaneous emission of an identical photon of the exact same wavelength/frequency/energy (some instead refer to this as "reflection" of the lower-energy photon). This explains the 2nd Law of Thermodynamics on a quantum basis, thus why low frequency/energy photons from a cold emitter cannot warm a warmer blackbody at a higher frequency/temperature/energy.
Since the emitting temperature of ~15um photons from atmospheric CO2 is -80C by Wein's & Planck's Laws (also explained in the reference below), these photons cannot possibly be thermalized/increase the energy or temperature of the much warmer Earth surface at +15C.
In the reference below, the Pauli exclusion principle is discussed on pages 215, 224, 230, 254, 268, and others. The Pauli exclusion principle prohibits more than 2 electrons from being in the same atomic or molecular orbital simultaneously. In the hot body, photons from a colder emitting source will not be able to join the higher-energy orbitals in the hot body both because they contain insufficient quantum energy, and those orbitals are already saturated with a maximum of 2 higher-quantum-energy electrons.
In the (simplified) Bohr theory, the energy well is very steep and any incoming photon at a lower-quantum-energy level than that of the target will not "catch and stick" on the sides of the energy well as illustrated in the figures below (from an earlier 4th edition of the Principles of Modern Chemistry, p. 540), thus, such lower-quantum-energy photons are not thermalized and cannot increase the energy/heat content/temperature of the hotter body.
Also in the reference below (beginning on page 236), microstates of molecules, for instance chemical bond energies and molecular orbitals are also subject to discrete quantum energy levels. A molecular orbital or chemical bond can only have a 1-2 electron wave functions at a time, analogous to the Pauli Exclusion Principle for atoms. A photon must contain sufficient quantum energy to increase such electrons to the next higher quantum energy level in order to be thermalized/increase the energy of the hotter body.
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