Do Climate Models Get Aerosol Transport to the Arctic Right?
Aerosols from pollution sources are assumed to influence Arctic climate by affecting Arctic clouds and darkening snow albedo. Pollution sources could be distant from the Arctic, and model simulation of the transport and removal of aerosols from the source to high latitudes is challenging. Most global climate models underestimate aerosols in the Arctic although the reasons causing this bias are not fully understood. For example, current climate models generally underpredict the surface concentration of soot or black carbon (BC) in the Arctic, a bias also seen in the Community Atmosphere Model version 5.1 (CAM5). In a new study, U.S. Department of Energy scientists at Pacific Northwest National Laboratory led a team investigating the uncertainty of CAM5 and simulated Arctic BC transport processes. They concluded that the features of simulated circulation regulating long-range BC transport are unlikely the most important cause of the large underprediction of surface BC in the Arctic. They configured the model to run two ways: first, driven with the climate-model winds and meteorology; second, with observed or reanalysis winds and meteorology. The climate-model version was not perfect. Although it simulated an “Arctic Oscillation” flow for example, it was not quite the same as the version with reanalysis winds, resulting in notable transport differences from Eastern Europe and northeast Asia. Nevertheless, the researchers found that the overall climatological circulation patterns simulated by the climate-model CAM5 generally resembled those from the reanalysis products, and that BC transport is very similar in both simulation sets. Therefore, the model biases must result from some other factors, such as errors in aerosol removal or emissions.
Ma, P.-L., P. J. Rasch, H. Wang, K. Zhang, R. C. Easter, S. Tilmes, J. D. Fast, X. Liu, J.-H. Yoon, and J.-F. Lamarque. 2013. “The Role of Circulation Features on Black Carbon Transport into the Arctic in the Community Atmosphere Model Version 5 (CAM5),” Journal of Geophysical Research: Atmospheres 118(10), 4657–69. DOI:10.1002/jgrd.50411.