An extremal principle is formulated and applied to a one-dimensional energy balance model. The principle is based on the maximization of the generation of available potential energy, and reduces to a maximization of the correlation between heating and temperature deviation. The maximization is subject to a constraint of global energy balance, and makes no reference to a dynamical transport mechanism. The maximizing temperature distribution has a larger meridional gradient than the observed temperature distribution. Our results suggest the general circulation operates at nearly its maximum efficiency.