A zonally averaged Climate model of the energy-balance type is examined. Recently published satellite measurements were used to improve existing parameterizations of planetary albedo and outgoing radiation in term of surface and sea level temperature. A realistic constant for the diffusion of energy was found by tuning the model to the present climate. For the actual solar constant both the present climate and an ice-covered earth are solutions of the model. They are extremely stable for temperature perturbations.
The effect of variation of the solar constant was investigated in detail. If the solar constant is decreased by 9–10% the warm solution (partial ice cover) jumps to the cold one (complete ice cover). Transition from the cold to the warm solution requires an increase of the solar constant to 109–110% of its present value. Therefore, we conclude that the model climate is much more stable with regard to variations in the solar input than has been assumed so far. This is caused mainly by our updated formulation of the outgoing radiation. Further experiments showed that our model is much more sensitive to changes in the outgoing radiation than to changes in the diffusivity for energy.