1 Potential Effects of Amazon Deforestation on Tropical Climate

The effects of Amazon deforestation have been simulated with a coupled general circulation model (GCM). The deforestation influences the global tropics, and in particular leads to significantly enhanced El Niño /Southern Oscillation (ENSO) variability. Diagnostic experiments with the coupled GCM are conducted to examine if changes in the coupled variability can be traced to the changes over the ocean found in an Amazon deforestation experiment done with climatological SST forcing of the atmospheric GCM. The diagnostic experiments indicate that the mechanism for the enhanced ENSO variability is that changes in the land surface properties cause changes in the mean surface wind stress in the tropical Pacific. These wind stress changes destabilize the mean state of the coupled system, and ENSO variability increases. The response of a simple Gill-type atmospheric model to the deforestation induced precipitation and surface temperature anomalies from the atmospheric GCM simulations is found. These indicate that the westerly wind stress anomalies over the far eastern Pacific are forced by the warmer surface temperatures over the deforested region rather than the reduced precipitation. Diagnoses with an intermediate coupled model of the tropical Pacific suggest that the wind stress anomalies over the far eastern Pacific are particularly important for destabilizing the mean state, and also that changes in the “weather noise ” forcing are probably not important in enhancing the ENSO variability. 3 1