New Multimodel Estimates of Aerosol Radiative Effects
Atmospheric aerosols are emitted by fossil fuel combustion and other human activities and affect climate by scattering (cooling) or absorbing (warming) incoming solar radiation. This effect depends on the particles’ chemical composition. While the net effect has been estimated to be cooling, the exact size of the effect is poorly constrained. A recent multimodel study, including contributions from U.S. Department of Energy researchers at Pacific Northwest National Laboratory, used 15 detailed global aerosol models to simulate and document changes in aerosol distribution and impact on the Earth’s energy balance over the industrial era. The direct aerosol effect (DAE) due to scattering and absorption of solar radiation by anthropogenic sulfate, black carbon (BC), organic aerosols, and other species from fossil fuel, biofuel, and biomass burning emissions was estimated by contrasting simulations using emissions for the years 1750 and 2000. Comparing these new model results to previous model versions from the team, they found very similar spreads in both total DAE and individual aerosol component radiative forcing. However, the radiative forcing of the total DAE is stronger negative, and radiative BC forcing from fossil fuel and biofuel emissions is stronger positive in the present study than in the previous one. Furthermore, models having large forcing for absorbing components also have large forcing for scattering components. The authors argue that the net aerosol forcing uncertainty is less than for individual aerosol components.
Myhre, G., B. H. Samset, M. Schulz, Y. Balkanski, S. Bauer, T. K. Berntsen, H. Bian, N. Bellouin, M. Chin, T. Diehl, R. C. Easter, J. Feichter, S. J. Ghan, D. Hauglustaine, T. Iversen, S. Kinne, A. Kirkevåg, J. F. Lamarque, G. Lin, X. Liu, M. T. Lund, G. Luo, X. Ma, T. van Noije, J. E. Penner, P. J. Rasch, A. Ruiz, Ø. Seland, R. B. Skeie, P. Stier, T. Takemura, K. Tsigaridis, P. Wang, Z. Wang, L. Xu, H. Yu, F. Yu, J. -H. Yoon, K. Zhang, H. Zhang, and C. Zhou. 2013. “Radiative Forcing of the Direct Aerosol Effect from AeroCom Phase II Simulations,” Atmospheric Chemistry and Physics 13, 1853–77. DOI: 10.5194/acp-13-1853-2013.