Topic summary
Water absorption
Extracted from the Wikipedia article Electromagnetic absorption by water.
Atmospheric effects
As well as absorbing radiation, water vapour occasionally emits radiation in all directions, according to the black-body emission curve for its current temperature overlaid on the water absorption spectrum. Much of this energy will be recaptured by other water molecules, but at higher altitudes, radiation sent towards space is less likely to be recaptured since there is less water available to recapture radiation at water-specific absorbing wavelengths. By the top of the troposphere, about 12 km above sea level, most water vapor condenses to liquid water or ice as it releases its heat of vapourization. After changing phase, liquid water and ice fall away to lower altitudes. This loss will be balanced by incoming water vapour rising via convection currents.