TRANSIENT-RESPONSE OF A COUPLED MODEL TO ESTIMATED CHANGES IN GREENHOUSE-GAS AND SULFATE CONCENTRATIONS

This study investigates changes in surface air temperature (SAT), hydr ology and the thermohaline circulation due to the the radiative forcin g of anthropogenic greenhouse gases and the direct radiative forcing ( DRF) of sulfate aerosols in the GFDL coupled ocean-atmosphere model. T hree 300-year model integrations are performed with increasing greenho use gas concentrations only, increasing sulfate aerosol concentrations only and increasing greenhouse gas and sulfate aerosol concentrations . A control integration is also performed keeping concentrations of su lfate and carbon dioxide fixed. The global annual mean SAT change when both greenhouse gases and sulfate aerosols are included is in better agreement with observations than when greenhouse gases alone are inclu ded. When the global annual mean SAT change from a model integration t hat includes only increases in greenhouse gases is added to that from a model integration that includes only increases in sulfate, the resul ting global SAT change is approximately equal to that from a model int egration that includes increases in both greenhouse gases and sulfate aerosol throughout the integration period. Similar results are found f or global annual mean precipitation changes and for the geographical d istribution of both SAT and precipitation changes indicating that the climate response is linearly additive for the two types of forcing con sidered here. Changes in the mid-continental summer dryness and thermo haline circulation are also briefly discussed.