Radiance and Absorption

Fig. 2

This chart, originally prepared by physicist R. A. Rhode, sets out in graphical form the results of an elaborate calculation of infrared absorbance. The percentages of absorbency (the grey areas) in the lower set of graphs need to be read in conjunction with the curved lines in the upper graph, which show how much infrared radiation is emitted by sun and earth before atmospheric absorbance takes place. (The colored areas show how much gets through the atmosphere.) The lower set shows how much of that emission is absorbed. In the two top charts, the higher the curved lines are, the greater the radiance and the greater the energy.  (Be aware that that the vertical scales of sun and earth radiation are vastly different from one another.) The lower the curved line, the less radiance and energy. Thus, for example, the CO2 absorbance band around 14.5 microns is obviously significant, while the smaller CO2 band around 4.3 microns is not because there is very little earth radiance in that range for it to catch. (In addition, most if not all radiation in that range is already absorbed.) The earth emissions graph at the top has several curves in order to show what happens to the theoretical maximum for earth emissions at different temperature levels - as average temperature rises, the curve shifts to the left. The middle, dark blue curve approximates current average earth temperature. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6174548