But the first order effect is the absorption and emission of radiation by water vapor, i.e., the greenhouse effect. (realclimate.org)
But that does not mean that emission of radiation at that wavelength = absorption of radiation at that wavelength. (scienceofdoom.com)
The principles of absorption and emission of radiation by various atmospheric trace gases like water vapor and CO2 rely on the theory of quantum mechanics. (scienceofdoom.com)