Maximum entropy production, cloud feedback, and climate change

A steady-state energy-balance climate model based on a global constraint of maximum entropy production is used to examine cloud feedback and the response of surface temperature T to doubled atmospheric CO2. The constraint ensures that change in zonal cloud amount øo necessarily involves change in the convergence KX of meridional energy flow. Without other feedbacks, the changes in øo, KX and T range from about 2%, 2 Wm-2 and 1.5 K respectively at the equator to -2%, -2 WM-2 and 0.5 K at the poles. Global-average cloud effectively remains unchanged with increasing CO2 and has little effect on global-average temperature. Global-average cloud decreases with increasing water vapour and amplifies the positive feedback of water vapour and lapse rate. The net result is less cloud at all latitudes and a rise in T of the order of 3 K at the equator and 1 K at the poles Ice-albedo and solar absorption feedbacks are not considered. Copynght 2007 by the American Geophysical Union.