Energy Balance Models Incorporating Evaporative Buffering of Equatorial Thermal Response

We describe two non-standard energy balance models which include effects of latent heat on climate sensitivity, and apply them to study sensitivity to uniform variations in insolation and changes in the concentration of atmospheric CO2. The Tropical Equatorial Constraint (TEC) model incorporates the proposal of Newell and Dopplick (1979) that evaporative losses from tropical sea surface strongly limit thermal response. The two phase model includes an approximate treatment of energy transfer both as sensible heat and as latent heat of water vapor. We compare the mathematical and physical assumptions underlying each model, and contrast their solutions with results from a standard model in which the diffusion coefficient remains constant with forcing. Both the TEC and two phase model produce stronger thermal response in polar regions than does the standard model. The TEC model shows that the implication of Newell and Dopplick (1979), that equatorial buffering will limit climate response to increasing CO2, is not justified when its global consequences are considered. The two phase model closely reproduces results for temperature change with latitude found by Manabe and Wetherald (1980) using a general circulation model. Polar amplification found in the two phase model is attributable to the behavior of a temperature dependent effective diffusion coefficient that increases with warming.