Do aircraft black carbon emissions affect cirrus clouds on the global scale?

Abstract

Potential modifications of cirrus clouds caused by aircraft-generated black carbon (BC) soot particles were investigated with a global atmospheric model. Many details of the role of BC in cirrus cloud formation are currently not well known. Therefore, hypothetical scenarios based on various assumptions on the ice nucleation efficiency of background and aircraft-induced BC particles were considered. Using these scenarios, the sensitivity of ice cloud microphysics to aviation-induced BC is studied. The model results suggest that cloud modifications induced by aircraft BC particles could change the ice crystal number concentration at northern midlatitudes significantly (10-40% changes of annual mean zonal averages at main flight altitudes), provided that such BC particles serve as efficient ice nuclei. The sign of the effect depends on the specific assumptions on aerosolinduced ice nucleation. These results demonstrate that significant cirrus cloud modifications by BC from aircraft and related climatic impacts cannot be excluded.