Leaving the last topic aside, the challenge in developing a simple description of the radiative transfer through the atmosphere, especially for use in computationally intensive circulation models, is to incorporate the combined effects of particle scattering and gaseous absorption in a computationally simple yet physically robust manner. The heart of the issue is to simplify the spectrally integrated absorption by atmospheric trace gases. The more traditional methods of the past that have achieved a modicum of success are the emissivity methods and band model methods typically described in any basic text on atmospheric radiation. These techniques unfortunately suffer from a lack of flexibility and rigor in treating overlapping scattering effects. This is a significant drawback as the need to treat scattering is crucial for the majority of problems that currently confront us. One technique that is both rigorous and simple yet presently of questionable computational efficiency is the method referred to as the correlated k-distribution (CKD).