Impacts of China's Anthropogenic Aerosol Emission Changes on Global Climate using Full-coupled CESM2 Model

In this study, we used the atmosphere-ocean coupled Community Earth System Model version 2 (CESM2) with full chemistry and the MOSAIC aerosol scheme to thoroughly assess the impacts of anthropogenic aerosol emission changes in China on global climate, with a special focus on Arctic. It is well-known that the economic activity of China increases tremendously over the last forty years. Large amounts of aerosols especially sulfate (as in form of SO2) and black carbon (BC), were emitted during this period. The aerosols can affect local and remote climate through interactions with radiation and clouds. To what extent these anthropogenic aerosols with increasing burdens impact global climate, especially Arctic, remains highly uncertain, and it must be studied in the context of fully coupled climate simulations.

In this study, we first improve the default CESM2 model by considering nitrate aerosol and adding heterogeneous production of sulfate aerosol. We conduct four cases, and each case with five ensemble simulations from 1970 to 2014. The four cases are 1) control experiment (with default CMIP6 emissions from 1970 to 2014), 2) sensitivity experiment 1970_SO2 (keep SO2 emission in China as the level of year 1970), 3) sensitivity experiment 1970_BC (similar to 1970_SO2, but for BC), and 4) sensitivity experiment 1970_both (both SO2 and BC emissions are kept as the level of 1970). By comparing the sensitivity experiments with the control experiment, we found that BC and SO2 emissions from China have very opposite effect on global climate (i.e. large surface temperature increase (decrease) comparing control with 1970_SO2 (1970_BC), especially over Arctic, which further leads to reduced (enhanced) ice cover, etc.). Non-linear effect can be observed when we compare the control case with 1970_both case, which is, very likely, caused by changes in ocean circulation directly.