Epochal westerly changes driven by shifts in anthropogenic aerosol emissions across Eurasia since 1940

The Eurasian subtropical westerly jet (ESWJ) is closely related to regional climate changes, such as heat waves over Eurasia. While the weakening of the ESWJ in summer since 1979 has been documented, earlier variations prior to the satellite era remain poorly understood. Here, using both reanalysis datasets and radiosonde observations, along with climate model simulations, we examine ESWJ changes from 1940 to 2020 and find that its post-1979 weakening is only part of broader interdecadal shift driven by the time-evolving sulfate aerosol distributions. This epochal shift in the ESWJ further led to a transition from decreasing to increasing trends in heatwave durations across Eurasia in the late 1970s. Before 1979, extensive sulfate emissions in Eurasia modulated the tropospheric temperature structure, leading to increased wind speeds along and south of the jet axis (~40°N). After 1979, reductions in sulfate aerosols over Europe and increased concentrations in Asia contributed to the weakening of the ESWJ. Additionally, moist adiabatic processes in the tropics, driven by rising greenhouse gas concentrations, favored an increase in ESWJ strength during both periods, partially offsetting the weakening induced by anthropogenic aerosol forcing after 1979. Our results highlight the crucial role of the time-evolving distribution of sulfate aerosols associated with different paces of industrial development across the Eurasian countries in driving the epochal westerly changes since the early 20 th century.