THE INFLUENCE OF GREENHOUSE WARMING ON THE ATMOSPHERIC COMPONENT OF THE HYDROLOGICAL CYCLE

An atmosphere-ocean climate box model is used to examine the influence of cloud feedback on the equilibria of the climate system. The model consists of three non-linear ordinary differential equations, which ar e simplified forms of the first law of thermodynamics for the atmosphe re and ocean and the continuity equation for the atmospheric component of the hydrological cycle. The mass continuity equation expresses the cloud liquid water content as a function of the evaporation rate from the ocean surface and the precipitation rate. Cloud formation release s latent heat. The model clouds also absorb solar energy at a rate con sistent with recent findings. The model simulates snow-ice albedo feed back, water vapour feedback and cloud feedback. The global mean precip itation and surface temperature are analysed as they respond to enhanc ed greenhouse warming. Model results show that cloud feedback can lead to the occurrence of multiple climate equilibria. Some of these are w armer than the present equilibrium, with increased precipitation, whil e others are colder, with reduced precipitation. If the cloud feedback is weak, enhanced greenhouse forcing leads to a small alteration of t he present equilibrium. If the cloud feedback is strong enough, the cl imate system can be forced into a warmer and wetter equilibrium.