The relative amount of scattering and absorbing aerosols is essential in determining the aerosol radiative and climate effects. Using reanalysis datasets and climate simulations, here we show that changes in the relative amount of scattering and absorbing aerosols in the Northern Hemisphere (NH) high latitudes, manifested as long term decreasing trends in aerosol single scattering albedo (SSA), have played an important role in driving the widening and weakening trends of the NH Hadley Circulation (HC) since early 1980s. Decreasing SSA in the NH middle and high latitudes can notably warm the troposphere there, thus reducing the equator-to-pole temperature gradient, increasing static stability in mid-latitude regions and leading to the widening and weakening trends of NH HC. Further analysis of the Coupled Model Intercomparison Project Phase 6 (CMIP6) aerosol-forcing-only simulations also supports the importance of SSA trends in perturbing NH HC through the above mechanism.

Aerosol Forcing, Aerosol Optical Property, Aerosol Scattering and Absorption, Hadley Circulation