Atmospheric aerosols exert a substantial influence on the Earth’s climate both directly by scattering and absorbing solar and terrestrial radiation, and indirectly by affecting the evolution and optical properties of clouds. Models are needed to better quantify global aerosol properties and trends to reduce uncertainties in model projections of future climate changes. A team of scientists, including Department of Energy researchers at Pacific Northwest National Laboratory, carried out the largest ever intercomparison of model-simulated size distributions among the new generation of global aerosol microphysics models within the AeroCom initiative. This international evaluation of 12 different global aerosol models found comparable realism is simulated using relatively simple and complex representations of aerosol microphysical properties. While complex representations predict the aerosol for a large number of size bins, simple treatments predict the number and mass concentrations for each of a small number of modes. All aerosol models simulated many aspects of the observed distribution of the aerosol realistically, but also suffered from consistent biases in some regions. The similarity of the biases across models suggests that all models are limited by common weaknesses in processes such as emissions and new particle formation. The findings here indicate that most of these global aerosol microphysics models are performing quite well in terms of global variation of the size distribution.