A Strong Anthropogenic Black Carbon Forcing Constrained by Pollution Trends Over China.

Estimates of the effective radiative forcing from aerosol‐radiation interaction (ERFari) of anthropogenic Black Carbon (BC) have been disputable and require better constraints. Here we find a substantial decline in atmospheric absorption of −5.79Wm−2decade−1 over eastern central China (ECC) responding to recent anthropogenic BC emission reductions. By combining the observational finding with advances from Coupled Model Intercomparison Project phase6 (CMIP6), we identify an emergent constraint on the ERFari of anthropogenic BC. We show that across CMIP6 models the simulated trends correlate well with simulated annual mean shortwave atmospheric absorption by anthropogenic BC over China. Making use of this emergent relationship allows us to constrain the aerosol absorption optical depth of anthropogenic BC and further provide a constrained range of 2.4–3.0 Wm−2 for its top‐of‐atmosphere ERFari over China, higher than existing estimates. Our work supports a strong warming effect of BC over China, and highlights the need to improve BC simulations over source regions. Plain Language Summary: Black Carbon (BC) widely affects the Earth system as a warming agent. However, estimates of the effective radiative forcing from aerosol‐radiation interaction (ERFari) by anthropogenic BC remain disputable with recent studies arguing for a downward revision, and therefore require better constraints. Here we find that atmospheric absorption declines evidently over eastern central China since 2005 due to reduced anthropogenic BC emissions. When analyzing results from the latest Coupled Model Intercomparison Project phase 6 (CMIP6) models, we further find that though the majority of models underestimate the observed trends, the simulated trends across CMIP6 models correlate well with simulated annual mean shortwave atmospheric absorption by anthropogenic BC over China. Combining this relationship with the observational range of the trends allows us to identify an emergent constraint on the aerosol absorption optical depth of anthropogenic BC and further provide an observationally constrained range of 2.4–3.0Wm−2 for its top‐of‐atmosphere ERFari. This estimate is substantially higher than all existing estimates, providing independent evidence to support a strong warming effect of BC over China. Our work also points out a common low bias of current global models in simulating BC over China, and highlights the need to improve BC simulations over source regions. Key Points: Atmospheric absorption declines substantially over eastern central China in response to recent reductions of anthropogenic Black Carbon (BC) emissionsThe observational finding combined with the latest Coupled Model Intercomparison Project phase 6 (CMIP6) models enable an emergent constraint on the anthropogenic BC forcing over ChinaThe constrained effective radiative forcing from aerosol‐radiation interaction of anthropogenic BC is higher than existing estimates [ABSTRACT FROM AUTHOR]