Climate Response to a Decade of Anthropogenic Emission Changes (2013-2023)

Global emission patterns have changed significantly in the past decade as regions around the world started various reduction policies, notably marked by China's Air Pollution Prevention and Control Action Plan and IMO's regulations on shipping emissions. However, the climate response to these regional emission changes has not been fully quantified. Using two climate models (CESM2 and GISS), we conducted 80-year simulations and analyzed the last 70 years to study the radiative effects of emission changes during 2013-2023. Through designed 4 experiments using ABaCAS EI, CMIP6, and SEIM shipping emission inventories, we separated the climate impacts from three main sources: China, regions outside China, and global shipping emissions. We then used the FaIR model to evaluate their temperature responses.

Our model simulations show remarkable consistency in top-of-atmosphere radiative changes despite differences in aerosol-cloud interaction parameterizations. The total effective radiative forcing (ERF) is approximately 0.15 W/m², with China's emission changes contributing the largest forcing (0.06-0.07 W/m²), followed by other regions (0.04-0.05 W/m²) and shipping (0.04-0.05 W/m²). Spatial analysis reveals significant positive forcing (>2 W/m²) over East Asia (20°N-45°N, 100°E-125°E) with notable downstream effects. CESM2, with its higher resolution, shows stronger aerosol transport signals over the Pacific, while GISS exhibits weaker signals in regions far from sources.

While both models differ in simulating cloud-aerosol interactions, CESM2's more detailed aerosol and cloud microphysics schemes and stronger aerosol-cloud-radiation coupling capture more transport and indirect effects, though the result also has larger uncertainties. In the North Pacific region, both CESM2 and GISS simulate strong positive radiative forcing change, showing significant radiative anomalies consistent with CERES satellite observations of outgoing shortwave radiation changes during 2013-2023. Our results indicate that China's emissions, through downwind transport, contribute more to these radiative changes than shipping emissions.

The FaIR model results suggest that China's emission reductions have led to approximately 0.025°C warming, while global emission changes have contributed about 0.05°C. We also evaluated potential future temperature trends based on temperature response functions. These findings improve our understanding of how regional emission changes affect the global climate system and highlight the importance of coordinated emission reduction strategies across regions and sectors, considering the role of both continental and maritime emissions in global radiative forcing patterns and their implications for future climate policies.