ABSTRACT
During the 1980s, atmospheric scientists discovered that General Circulation Models (GCMs) of the atmosphere failed to predict contemporary climates adequately, unless the biosphere was properly specified. GCM-climate sensitivity to the global pattern of surface roughness, which is largely a function of vegetation, is manifested as a twofold variation in the surface wind velocity. Changes in the surface roughness specification also made a major difference in divergence of mass and energy in the low latitudes and, therefore, rainfall patterns in these regions. GCM temperature-field sensitivity to evapotranspiration, in contrast with the 'bucket'evaporation in early models, was + 25°C over mid-latitude continents, and the intensity of global pressure-fields in the same study was 10mb, a very large effect. GCM sensitivity to land-cover albedo is clearly evident in the transition between dry and moist convection in the low latitudes and, thus, realized rainfall. Sensitivity experiments using a doubled atmospheric carbon dioxide showed new patterns of climate, which imply new patterns of vegetation and thus changed surface roughness, evapotranspiration and albedo. Results of the GCMs of the 1980s clearly indicate that the old paradigm that says vegetation controls climate only at the microscale must be abandoned. The biosphere in the current generation GCMs is a static boundary condition, but clearly it should not be. The
feedback loops with vegetation controlling climate are not yet on the GCM drawing boards; they will require new Global Biosphere Databases at a spatial resolution greater than those of the next generation of GCMs.
