Surface temperature sensitivities in a multiple cloud radiative-convective model with a constant and pressure dependent critical lapse rate

A comparison is made of the surface temperature sensitivities in the Hummel–Kuhn radiative–convective model with fixed clouds, but without water vapor transport, using first the constant critical lapse rate of 6.5 K/km and then with pressure-dependent moist adiabatic critical lapse rates. The moist adiabatic critical lapse rate formulation is shown to yield consistently smaller surface temperature sensitivities to parameter variations than those yielded from using the traditional 6.5 K/km.

For a doubling of carbon dioxide (300 p.p.m.v. to 600 p.p.m.v.). the surface temperature increase is 1.29 K with moist adiabatic lapse rates compared with 1.83 K for the 6.5 K/km formulation. In addition, the surface temperature sensitivities to changes in surface relative humidity, surface albedo, and cloud amounts are shown to be nonlinear with pressure-dependent critical lapse rates rather than linear as with the constant 6.5 K/km.