Vast gaps remain in our ability to simulate many of the mesoscale processes in numerical models. It will also depend on their ability to represent properly the interactions between mesoscale systems and cloud microphysical processes involving latent heat release. The effect that precipitation processes have on diffusion, transport, and scavenging of chemical species important to public safety and air quality also demands intensive research. Similarly, the importance of surface characteristics to the development of mesoscale precipitation systems underscores the need for adequate information concerning the spatial and temporal patterns of evapotranspiration and solar radiation, important terms in the surface energy balance. Many of the issues just discussed are equally important at the interannual and longer time scales.
Clouds are the most crucial factor causing uncertainties in model estimates of global warming.
Changes in water vapor in the upper troposphere, although small in absolute amount compared with the lower troposphere, may potentially be far more important in determining warming near the earth's surface. Significant research progress will follow from the development of models that furnish reliable predictions of cloudiness and its radiative impacts from a knowledge of the water vapor fields and atmospheric dynamics. While these resolutions are capable of representing the larger-scale atmospheric circulation, they are too crude to simulate explicitly the physical processes that generate clouds and redistribute and condense water vapor. Thus, climate models fail to determine uniquely how clouds and water vapor contribute to global-scale temperature changes, and are clearly incapable of depicting regional climate changes. The capability of these models to predict regional climates depends on increased model resolution and better parameterization of the physical processes inherent in mesoscale systems.