“General Coldness of Climate Models” and the Second Law: Implications for Modeling the Earth System

Abstract

Abstract Motivated by the circumstantial evidence of the pervasive nature of the “general coldness” of climate model simulations, a theoretical analysis is made of the model response expected from the presence of both physical and aphysical sources of entropy under the joint conditions that the net flux of energy through the upper and lower boundaries of the atmosphere and the isentropic temporally, areally integrated entropy source must vanish. These joint conditions are essential for a simulated global climate state to be without drift. The application of these conditions in the presence of positive definite aphysical entropy sources leads to the conclusion that the model-simulated climate state will be characterized by a general coldness, in particular in the upper polar troposphere and lower tropical troposphere as observed in 104 out of 105 possible outcomes from 35 different simulations by 14 climate models. In assessing the magnitude of this effect, a 10°C bias in mean temperature corresponds with ...