CLIMATIC VARIABILITY WITHIN AN EQUILIBRIUM GREENHOUSE SIMULATION

A simulation of the possible consequences of a doubling of the CO2 con tent of the atmosphere has been performed with a low resolution global climatic model. The model included the diurnal and seasonal cycles, c omputed sea ice amount and cloud cover, and used implied oceanic heat fluxes to represent transport processes in the oceans. A highly respon sive 2-layer soil moisture formulation was also incorporated. Twenty y ear equilibrated simulations for control (1 x CO2) and greenhouse (2 x CO2) conditions were generated. The major emphasis of the analysis pr esent ed here is on the intra-annual and interannual variability of th e greenhouse run with respect to the control run. This revealed consid erable differences from the time-averaged results with occasions of ma rked positive and negative temperature deviations. Of particular inter est were the periods of negative temperature departures compared to th e control run which were identified, especially over the Northern Hemi sphere continents. Temporal and spatial precipitation and soil moistur e anomalies also occurred, some of which were related to the surface t emperature changes. Substantial sea surface temperature anomalies were apparent in the greenhouse run, indicating that a source of climatic forcing existed in addition to that due to doubling of the CO2. Compar ison of the intra-annual and interannual variability of the control ru n with that of the greenhouse run suggests that, in many situations, i t will be difficult to identify a greenhouse signal against the intrin sic natural variability of the climatic system.