A REEXAMINATION OF THE GREENHOUSE-EFFECT DUE TO CFC-11 AND CFC-12

Employing the most recent laboratory absorption-coefficient data1 on the thermal infrared (i.r.) bands of CFC-11 (CFCl3) and CFC-12 (CF2Cl2), which were measured at several temperatures relevant to the troposphere and the stratosphere, the greenhouse effect produced by these two CFCs has been reexamined. The effect upon the atmospheric radiative fluxes due to the temperature dependence of the absorption coefficient, especially in the many hot bands present in this spectral region, has been studied. The validity of the often used optically-thin approximation has been scrutinized in view of the observed enhancement in the absorption by the CFCs at low temperatures. The influence of absorption by water vapor on the radiative transfer through columns of CFC-11 and CFC-12 has also been considered. It has been shown that, even though each of these individual refinements may modify the previously estimated effect due to the CFCs by a small amount only, the collective effect may be a non-negligible 35% change in the surface-troposphere heating for every ppbv of CFC-11 and CFC-12 each introduced into a model atmosphere.