On the effect of CO2 on atmospheric heating rates

A high resolution longwave radiative transfer model has been developed to investigate the effect of increasing CO₂ concentrations on longwave fluxes and heating rates. High spectral resolution has been used in evaluating transmission functions in the 15 μm CO₂ band region with allowance being made for H₂O overlap. Comparison of the results of this model and those of the model of Manabe and Wetherald suggest that the Manabe-Wetherald model is quite accurate and that both models produce similar changes in the heating rate for doubled CO₂ concentrations. These changes are quite small (< 0.1 K day^-1) in the troposphere and are of the same order of magnitude or smaller than the estimated accuracy of the models. Larger differences are noted in the stratosphere but model errors are also larger in this region. Through the use of a radiative-convective model it was found that the small changes in the tropospheric heating rate are responsible for more than half of the computed surface temperature change.