"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."Many have asked why a photon with insufficient quantum energy cannot be thermalized or increase the heat energy of a warmer blackbody. This is the basis of blackbody radiation absorption and emission and Planck's Quantum Hypothesis, as is very well described beginning on page 146 of "Principles of Modern Chemistry, 7th Edition" excerpted below.
To falsely assume that a photon of any energy level can be thermalized by a blackbody at a given temperature would result in the dashed red and blue function in fig 4.8 below, which does not happen in nature. Therefore, Planck devised quantum theory to explain why blackbodies instead follow a Planck curve shown by the solid blue and red lines below (corresponding to different blackbody temperatures) and contain "cutoff frequencies for thermalization":