The Overlapping Effect of Greenhouse Gases Absorption Bands on CO2 Thermal Radiative Effect

The effect of overlapping of atmospheric H2O, CO2, O3, N2O, and CH4 absorption bands on the total thermal cooling rates and the radiative perturbation due to the doubling CO2 abundance are investigated using an exact linebyline integration algorithm. It is found that the overlapping effect plays an important role on the calculation of thermal cooling rates. Among the five main infrared absorbers, the overlapping effect of N2O and CH4 can be neglected as their little contribution. The influence of overlapping effect on the CO2 thermal radiative is to decrease the enhanced greenhouse effect due to increased absorber announces which are mainly contributed by the 15 μm CO2 band wings and the secondary weaker bands centred at 960 cm-1 and 1064 cm-1. In vertical, overlapping effect has slight influence on the radiative perturbation in stratosphere, but plays a significant role in troposphere and surface. The net effect of the overlapping absorption is to transform the troposphere from cooling to warming, and to decrease the strength of surface warming caused by CO2 increase. Additionally, overlapping effect exhibits strong seasonal and latitudinal variations due primarily to changes in H2O concentration.