Negligible contribution from aerosols to recent trends in Earth's energy imbalance

During the 21st century, Earth's energy imbalance (EEI) at the top of atmosphere has markedly increased because of greater absorbed shortwave (SW) rather than reduced outgoing longwave radiation. Previous studies using single-forcing (aerosol-only) experiments attributed approximately half of the positive SW trend to reductions in anthropogenic aerosols, particularly in the Northern Hemisphere (NH). In contrast, our analysis using observations and reanalysis indicates that both aerosol-radiation and aerosol-cloud interactions have made a negligible contribution to recent EEI trends. While NH anthropogenic aerosols have decreased, enhanced emissions from wildfires and volcanic activity in the Southern Hemisphere (SH) have produced comparable increases, yielding little net global impact. This hemispheric compensation also suggests that model-based estimates may overestimate aerosol influence by overlooking SH aerosol contributions. Despite uncertainties in aerosol proxies, the consistent results from two complementary proxies-satellite-derived aerosol index and reanalysis-based sulfate mass concentration-highlight the importance of accounting for natural source aerosols when assessing EEI trends.