8.2.5 Aerosol Modelling and Atmospheric Chemistry

Climate simulations including atmospheric aerosols with chemical transport have greatly improved since the TAR. Simulated global aerosol distributions are better compared with observations, especially satellite data (e.g., Advanced Very High Resolution Radar (AVHRR), Moderate Resolution Imaging Spectroradiometer (MODIS), Multi-angle Imaging Spectroradiometer (MISR), Polarization and Directionality of the Earth’s Reflectance (POLDER), Total Ozone Mapping Spectrometer (TOMS)), the ground-based network (Aerosol Robotic Network; AERONET) and many measurement campaigns (e.g., Chin et al., 2002; Takemura et al., 2002). The global Aerosol Model Intercomparison project, AeroCom, has also been initiated in order to improve understanding of uncertainties of model estimates, and to reduce them (Kinne et al., 2003). These comparisons, combined with cloud observations, should result in improved confidence in the estimation of the aerosol direct and indirect radiative forcing (e.g., Ghan et al., 2001a,b; Lohmann and Lesins, 2002; Takemura et al., 2005). Interactive aerosol sub-component models have been incorporated in some of the climate models used in Chapter 10 (HadGEM1 and MIROC). Some models also include indirect aerosol effects (e.g., Takemura et al., 2005); however, the formulation of these processes is still the subject of much research.

Interactive atmospheric chemistry components are not generally included in the models used in this report. However, CCSM3 includes the modification of greenhouse gas concentrations by chemical processes and conversion of sulphur dioxide and dimethyl sulphide to sulphur aerosols.