Changes in atmospheric sulfur burdens and concentrations and resulting radiative forcings under IPCCSRES emission scenarios for 1990-2100

[ 1] Simulations of the global sulfur cycle under the IPCC SRES scenarios have been performed. Sulfur dioxide and sulfate burdens, as well as the direct and first indirect radiative forcing (RF) by sulfate aerosols only, are presented for the period 1990 to 2100. By 2100, global sulfur emission rates decline everywhere in all scenarios. At that time, the anthropogenic sulfate burden ranges from 0.34 to 1.03 times the 1990 value of 0.47 Tg S. Direct and indirect global and annually mean RFs relative to the year 1990 are near 0 or positive ( range of - 0.07 to 0.28 Wm(-2) and 0.01 to 0.38 Wm(-2) for the direct and indirect effects, respectively). For reference these forcings amount respectively to - 0.42 and - 0.79 Wm(-2) in 1990 relative to preindustrial conditions ( around 1750). Sulfur aerosols will therefore induce a smaller cooling effect in 2100 than in 1990 relative to preindustrial conditions. For the period 1990 to 2100, the forcing efficiencies ( computed relatively to 1990) are fairly constant for the direct effect ( around - 160 W ( g sulfate)(-1)). The forcing efficiencies for the indirect effect are around - 200 and - 100 W ( g sulfate)(-1) for negative and positive burden differences, respectively. This is due to a shift in regional patterns of emissions and a saturation in the indirect effect. The simulated annually averaged SO2 concentrations for A1B scenario in 2020 are close to air quality objectives for public health in some parts of Africa and exceed these objectives in some parts of China and Korea. Moreover, sulfate deposition rates are estimated to increase by 200% from the present level in East and Southeast Asia. This shows that Asia may experience in the future sulfur-related environmental and human health problems as important as Europe and the United States did in the 1970s.