Aerosol Radiative Forcing Uncertainties Affected by Climate Model
Atmospheric aerosols are emitted by fossil fuel combustion and other human activities and affect climate by scattering (cooling) or absorbing (warming) incoming solar radiation. The effect depends on the particles’ chemical composition. However, the estimate of how much aerosols warm or cool climate is uncertain, as various models have calculated a wide range of forcings. These forcing uncertainties come from differing aerosol simulation algorithms that have differing aerosol-climate interactions (such as aerosol transport and rainout) and different background climate properties such as surface brightness. A recent study by a group of climate scientists, including U.S. Department of Energy-funded researchers at Pacific Northwest National Laboratory, found a way to isolate the uncertainty due to the aerosol calculations from the influence of the models’ different background climates. The team used 12 different climate models and prescribed the same aerosol fields for each model. They found that a surprisingly large diversity in aerosol forcing comes from the host climate models’ differences in model-simulated clouds and surface properties, which could explain about half the overall sulfate aerosol forcing diversity in the forcing estimate. The study demonstrates the importance of considering the aerosol climate context when working to reduce uncertainty in forcing estimates.
Stier, P., N. A. J. Schutgens, H. Bian, O. Boucher, M. Chin, S. Ghan, N. Huneeus, S. Kinne, G. Lin , G. Myhre, J. E. Penner, C. Randles, B. Samset, M. Schulz, H. Yu, and C. Zhou. 2013. “Host Model Uncertainties in Aerosol Radiative Forcing Estimates: Results from the AeroCom Prescribed Intercomparison Study,” Atmospheric Chemistry and Physics 13, 3245–70. DOI: 10.5194/acp-13-3245-2013.