Developing an interactive biosphere for global climate models

A highly generalised (five classes) grouping of Holdridge life zones, has been used to derive predicted 'natural' ecosystems for the present day climate using temperature and precipitation derived from two experiments undertaken with the NCAR Community Climate Model. These predictions differ from one another and both differ significantly from the prescribed classification groupings of ecosystem complexes used with a state-of-the-art land surface parameterization submodel, the Biosphere-Atmosphere Transfer Scheme. The highly generalised groupings show relatively little sensitivity to the temperature changes induced by doubling atmospheric CO₂ but greater response when precipitation is also modified. All the doubled-CO₂ scenarios predict increased 'desert' areas although these future climatically-induced changes to the global-scale ecology are very much smaller than the extensive disturbances already caused by mankind's land clearance and poor agriculture. Land-use change rendered 13% of the Earth's land surface 'desert' whereas the most pessimistic doubled-CO₂ result gives rise to only a 2% increase in 'desert' area.