Projections of Climate Forcing by Sulfate, Organic Aerosols, Dust, and Sea Salt: Results from the IPCC Model Intercomparison Workshop

New projections of emissions for anthropogenic compounds have been developed in the Special Report on Emissions Scenarios by the IPCC for the time period 2000 to 2100. This paper presents the results of an IPCC model intercomparison workshop, held in July 1999, to determine the magnitude and uncertainty in aerosol forcing of climate associated with these new emissions scenarios. The uncertainty in model calculations was judged by both model inter-comparison and comparison of model results with both ground-based aerosol concentrations and satellite-based aerosol optical depths. Workshop simulations were designed to separately examine direct and indirect forcing by the anthropogenic aerosol components, as well as the importance of feedbacks associated with climate change on emissions of natural aerosols. Changes in the emissions of dimethyl sulfide (associated with changes in ocean temperature and wind speed), sea salt (associated with changes in wind speed), dust mobilization (associated with changes in wind speed and soil moisture) and natural organic compounds (associated with changes in temperature, light levels, humidity and wind speed) were estimated and the impact of these changes on indirect forcing was estimated. Estimates for both direct and indirect forcing as well as the uncertainty in this forcing will be presented.