Quantitative Comparison of a Hierarchy of Commonly Used Planetary Climate Energy Balance Models

Abstract

The objective of this paper is to examine the effect of the various simplifications inherent in commonly-used planetary energy balance climate models (EBMs). Specifically, we look at the zero-dimensional (0-d) radiative equilibrium model, the 1-d radiative equilibrium model, and the 1-d radiative-convective equilibrium (RCE) model. Each of these models make fundamental steps towards a well-represented Earth system model, and make different simplifications and assumptions in the process. We seek to evaluate the effects these assumptions have on key thermal quantities of the system (OLR / outgoing longwave radiation, surface temperature, etc.). These evaluations lead us to identify contexts for each model wherein it remains a valid option to accurately replicate a system. The 0-d model fails to account for the greenhouse effect’s impact on energetics, thus predicting an erroneously-low surface temperature and low OLR. It instead requires an emissivity coefficient ~ 0.619 to balance OLR and temperature and model the Earth system. The 1-d radiative equilibrium model is a significant improvement on its predecessor, creating a stratospheric thermal profile reasonably similar to that of the Earth. The strong low-altitude temperature lapse rate and convective instability near the surface, however, slightly diminishes the validity of the low-level thermal profile – a drawback the RCE model appears to resolve with the addition of convective and boundary layer components. We conclude that the 0-d radiative equilibrium is best suited to isothermal atmospheres, the 1-d radiative equilibrium model to non-isothermal atmospheres where convection is suppressed, and the 1-d RCE model to convectively-active atmospheres.