ABSTRACT

The climate of the Earth is, to a considerable degree, controlled by the terrestrial biosphere. Its surface properties (albedo and roughness) are important parameters for the surface exchanges of energy and momentum. Even more important are the tightly coupled exchange fluxes of water, carbon dioxide, and oxygen both by diffusion through the stomata of leaves during photosynthesis and through soils and organic matter by respiration. By means of process models of terrestrial biogeochemistry and coupling these to general circulation models in various ways, one can attempt to estimate the degree to which this terrestrial biospheric control is effective. Furthermore, the exchanges of these gases are reflected in spatiotemporal variations of their atmospheric distribution. Modeling of these patterns and comparing them to observations constitutes a powerful tool to evaluate the performance of terrestrial biogeochemical models.

A recent sensitivity model simulation with the European Centre Hamburg Atmosphere Model (ECHAM) general circulation model demonstrates that the presence or absence of terrestrial vegetation induces near surface land temperature changes of as much as 8 °C, doubled precipitation, and nearly threefold changes in evapotranspiration. The largest contributions to these changes are found to be caused by the enhanced surface water recycling in the presence of a “green world, ” as compared with a global desert. The simulation sets upper bounds on possible climate modifications induced by anthropogenic changes in land use.