Planck’s Law for Spectral Radiance From a Black Body
The spectral radiance of radiation emitted by a black body increases with the absolute temperature (K) of the body according to Planck’s law. Only radiation from a black body that is warmer than Earth can increase the spectral amount and the frequency of peak spectral radiation (dashed black line) warming Earth. The peak spectral radiance of terrestrial radiation (black line) is 69 times less than the peak spectral radiance of solar radiation at the top of the atmosphere (Sun TOA) (red dashed line). The energy contained within radiation increases with increasing frequency according to Planck’s postulate (E=hν) (green dot-dashed line). The infrared energy around 20 terahertz (14,900 nm) radiated by Earth and available to be absorbed by greenhouse gases is 48 times less than the solar ultraviolet energy around 967 terahertz (310 nm) absorbed by ozone or allowed to reach Earth when ozone is depleted (red circles).