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

Potential cirrus modifications caused by aircraft‐produced black carbon (BC) particles via heterogeneous ice nucleation were studied with a general circulation model. Since the role of BC in cirrus cloud formation is currently not well known, 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 perturbations 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 aerosol‐induced ice nucleation. These results demonstrate that, based on the current knowledge, significant cirrus modifications by BC from aircraft cannot be excluded.