Air in the atmosphere is at relatively low temperatures, compared with the sun. While emission of short wavelength radiation (visible and ultraviolet) by the sun is extremely important, emission of radiation at those same wavelengths by the cooler earth-atmosphere system is insignificant. Absorption of incoming solar radiation by the atmosphere is a significant factor to include in earth-system science considerations even though the absorption is relatively small compared with the amount transmitted through the air. Scattering of solar radiation by the atmosphere (even the clear atmosphere) is a significant process and should be taken into account in earth-system science considerations.