The results of simple zonal energy balance climate models are rather sensitive to the parameterizations used to calculate the fluxes of solar radiation absorbed, thermal radiation emitted and energy transported by the atmosphere and oceans. For this reason results are examined for North's (1975a) constant coefficient diffusion model using climatologically consistent radiation parameterizations. With these radiation parameterizations, the calculated climate is less sensitive to changes in the incident solar radiation than was previously found using other parameterizations. In addition, how the model's results are influenced by the biofeedback mechanism recently proposed by Cess (1978) is studied. This feedback accounts for changes in the surface albedo caused by changes in the vegetation that might accompany climate change. Based on the model results, this feedback could be an important link between the climate and the earth's orbit around the sun.