A Modeling Study on the Climate Impacts of Black Carbon Aerosols

The role of black carbon (BC) aerosols in climate change is important because of its strong capability in causing extinction of solar radiation. A three-dimensional interactive aerosol-climate model has been used to study the climatic impact of BC. The interannual variations of BC solar forcing derived from 20-year transient integrations are up to 4 times as large as the means mainly related to changes in cloud cover, snow depth (about ±20% over many highor even mid-latitude regions in Northern Hemisphere) and thus the surface albedo, all caused by BC solar forcing itself. With an absolute amount three times higher than that of the top of the atmosphere (TOA) forcing, the surface forcing of BC is an extremely important factor in analyzing the climate impact of BC. BC aerosols cause a “cloud burning” effect in several polluted regions and a “cloud enhancing” effect in some high-latitude sites. Combined with BC-caused changes in surface albedo, this is defined as a non-Twomey-Albrecht indirect forcing by BC, which alters the radiative budgets by changing cloud cover and some land-surface properties thermodynamically rather than microphysically. The result of this study does not indicate that BC aerosols contribute to a significant increase in land-surface temperature with annual emissions of 14 TgC. The calculated surface temperature change is determined by a subtle balance among changes in surface energy sources and sinks as well as changes in the hydrological cycle, all caused by BC radiative forcing. The result of this study shows that the influence of BC aerosols on climate and environment at the regional scale is more significant than at the global scale. Several important feedbacks between BC radiative effect and climate dynamics revealed in this study suggest the importance of using interactive aerosol-climate models to address the issues related to the climate impacts of aerosols.