Comparison of radiative-convective models with constant and pressure-dependent lapse rates

In the current generation of radiative-convective models a constant value for the critical atmospheric lapse rate, generally 6.5 K/km, is used. However, the moist adiabatic lapse rates are a better approximation for use in simple climate models. Thus, a comparison of temperature profiles with critical constant and moist adiabatic lapse rates has been made for a one-dimensional radiative-convective model. The commonly used lapse rate of 6.5 K/km yields surface temperatures some 1 to 3 K higher than with the use of moist adiabatic lapse rates for both clear sky conditions and a single effective cloud. When multiple clouds are included the constant lapse rate of 6.5 K/km yields the lower surface temperatures. More importantly, the surface temperature generated from the constant lapse rate formulation is more sensitive to changes in carbon dioxide, relative humidity, cloud cover, and surface albedo. For a doubling of CO2 the moist adiabatic lapse rate formulation yields surface temperature changes 25 to 60% smaller than does a constant 6.5 K/km lapse rate depending on the cloud treatment.