03/15/2013
Aerosol Radiative Forcing in Historical and Future Climate Simulations
Summary
Atmospheric aerosols from human activities such as fossil fuel combustion influence surface temperatures, mainly contributing to climate cooling. Although aerosol concentrations increased during the past century, they have been declining in many regions due to the recent imposition of pollution controls. A team of scientists, including U.S. Department of Energy researchers at Pacific Northwest National Laboratory, evaluated 10 Atmospheric Chemistry and Climate Model Intercomparison Project (ACCMIP) model simulations of aerosols and estimated the climate impacts for past and future simulations. The team found that the models represent present-day total aerosol optical depth (AOD), a measure of atmospheric blockage of radiation, relatively well, though many models underestimate AOD. Contributions from individual aerosol chemical components are quite different among models. The models captured most AOD trends during the years 1980 to 2000, but under-predicted increases over the Yellow/Eastern Sea. They strongly underestimate absorbing AOD trends from black carbon or soot in many regions. This study found climate feedbacks, including cloud responses, contribute substantially (35% to 58%) to modeled historical aerosol radiative forcing. The largest 1850 to 2000
negative aerosol forcings (leading to cooling) are over and near Europe, South and East Asia, and North America, which are major emission regions. There remains considerable uncertainty in how climate feedbacks to aerosols, including cloud responses, are influencing climate.
References
Shindell, D. T., J.-F. Lamarque, M. Schulz, M. Flanner, C. Jiao, M. Chin, P. Young, Y. H. Lee, L. Rotstayn, G.
Milly, G. Faluvegi, Y. Balkanski, W. J. Collins, A. J. Conley, S. Dalsoren, R. Easter, S. Ghan, L. Horowitz, X. Liu, G. Myhre, T. Nagashima, V. Naik, S. Rumbold, R. Skeie, K. Sudo, S. Szopa, T. Takemura, A. Voulgarakis, J.-H. Yoon, and F. Lo. 2013. “Radiative Forcing in the ACCMIP Historical and Future Climate Simulations,” Atmospheric Chemistry and Physics 13, 2939–74. DOI:10.5194/acp-13-2939-2013.