Climatic Impacts of International Shipping Emissions in CESM-MARC

International shipping contributes about 0.5% to 3.5% to the global sulfur emission. It is well known that sulfate particles in the atmosphere not only can modulate Earth’s radiation budget but also sever as cloud and ice nuclei. In this work, a general circulation model (i.e. CESM) coupled with an sophisticated, multi-mode aerosol model (MARC) that explicitly treats the aerosol–cloud interactions is used to quantify the radiative forcing of international shipping emissions as well as their impacts on climate by interacting with clouds. The preliminary model results show that the shipping emissions can increase the total cloud water path and the droplet number concentration by about 50% and more than 100% in the regions of frequent shipping tracks (i.e. in the northern Pacific Ocean and Atlantic Ocean), respectively. The cloud shortwave radiative forcing due to shipping emissions is much larger than the direct shortwave radiative forcing. Preliminary results regarding the climate response to shipping emissions mainly through aerosol effects will also be discussed.