A Natural Constraint to Anthropogenic Global Warming

Abstract

Computer model projections suggest that unconstrained emissions of carbon dioxide and other greenhouse gases by human activity will cause the global average temperature to rise by at least 2 °C and possibly as much as 4.5 °C toward the end of the 21^st century as equivalent concentrations of carbon dioxide in the atmosphere nearly double. A well-specified analysis of the surface temperature response to global warming presented here suggests that global average surface temperature is unlikely to rise beyond 1 °C. This analysis identifies the rate of increase of evaporation (and latent heat exchange) with temperature at the surface as a critical restraining factor that damps surface temperature response to radiative forcing. It is noted that current computer models of the climate system apparently underestimate the rate of increase of surface evaporation with temperature leading to a gross exaggeration of the surface temperature response to radiative forcing.