The Dominant Patterns of Evolving Historical Industrial Aerosol and Biomass Burning Emissions and Their Climate Impacts Via Atmospheric and Oceanic Pathways

The spatial pattern of industrial aerosol emissions has changed markedly over the course of the 20th century. Changes in their spatial distribution have likely altered the strength and spatial pattern of their climate impact. Biomass burning (BMB) emissions, another important aerosol source with anthropogenic contributions, have co-evolved with industrial emissions. However, the climate impact of evolving aerosol emissions from both industrial and BMB sources is less known. Using atmosphere-only simulations driven by historical industrial and BMB emissions, we identify two leading patterns of these aerosol emissions: the first mode depicts the continuous increase in aerosol emissions over low latitudes, while the second mode depicts aerosol emissions over Northern Hemisphere (NH) mid-latitudes peaking in the 1980s. Our results suggest that sea surface temperature (SST)-mediated forcing dominates the large-scale atmospheric response to these aerosol modes. However, radiative forcing is important locally and partially counteracts SST-mediated forcing in remote regions. This sheds light on how SST-mediated forcing, as well as remote radiative forcing, can modify the effects of local forcings and suggests that, in terms of decadal (low-frequency) transient aerosol emission impact, the SST-mediated response co-evolves with the radiative forced response. Reconstruction analysis reveals that the first mode, associated with low-latitude aerosol emissions, dominates the precipitation trend driven by industrial aerosol and BMB emissions from 1940-2019 and contributes considerably to historical precipitation trends. The second mode, associated with increased low-latitude and decreased mid-latitude emissions, dominates from 1980-2019. This highlights the crucial role of low-latitude aerosol emissions in historical precipitation changes. Industrial and BMB aerosol emissions both need to be considered for hydrology predictions under global warming, especially as projected aerosol emission reductions are expected to occur mainly in low-latitude regions.