Overlapping effect of atmospheric H<sub>2</sub>O, CO<sub>2</sub> and O<sub>3</sub> on the CO<sub>2</sub> radiative effect

Abstract

The effect of overlapping of atmospheric H2O, CO2 and O3 absorption bands on the radiation budget perturbation caused by CO2 doubling is investigated. Since the effect depends on the amount of gases in the atmosphere as well as on the strength of the absorption bands, we examine the effect associated with the variation of gas abundance using a narrow band representation for the absorption bands. This band representation allows for the absorption band structure and thus accounts for the correlation of the spectral feature of the absorbing gases.It is found that the presence of H2O and O3 has a relatively small influence on the CO2-induced perturbation of both solar and thermal radiation in the stratosphere. However, in troposphere and surface, the overlapping effect appears to be quite significant and changes the vertical distribution of the CO2-induced radiation energy perturbation. For example, in the infrared, the effect is to reduce the effectiveness for CO2 to emit and in the mean time increases the tropospheric absorption of downward thermal flux from the stratosphere due to CO2 increase; the net effect of the overlapping of gases is to increase the tropospheric warming and decrease the surface warming caused by CO2 increase. It is also found that the overlapping effect exhibits strong seasonal and latitudinal variations due primarily to variations in atmospheric H2O.