An Analytical Model of Atmospheric Feedback and Global Temperature Change

Abstract

An analytical model of the globally averaged surface temperature response to changes in radiative forcing induced by greenhouse gases is developed from a time-dependent version of the global energy budget. The model clarifies the role of feedback and system heat capacity in controlling the magnitude and rate of response. Observed seasonal changes in surface temperature, radiative fluxes, and planetary albedo are combined to estimate the atmospheric feedback and the net gain of the system. A simple model of ocean upwelling and diffusion then yields an estimate of the heat capacity and thus the time constant of the system. The observed global temperature change from 1900 to 1990 is used to calibrate the model and refine the estimate of the time constant. The model provides a framework for comparing numerical models, including time-dependent ocean-atmosphere models used by the Intergovernmental Panel on Climate Change to estimate expected global temperature changes. When integrable analytical approximations to greenhouse-forcing scenarios are combined with the model, completely analytical representations of the global temperature change are readily obtained, yielding numerical estimates that agree with those of more complex models.