Surface temperature dependence of stratospheric sulfate aerosol clear-sky forcing and feedback

Stratospheric sulfate aerosols, produced by explosive volcanic eruptions or through artificial stratospheric aerosol injection for solar radiation management, can perturb Earth’s radiative budget for several years. However, the understanding of the state dependence of aerosol forcing and its effect on radiative feedback remains incomplete.

We use a one-dimensional radiative–convective equilibrium model of the tropical atmosphere to quantify the clear-sky forcing and feedback contributions from aerosol absorbing and re-emitting longwave radiation, stratospheric heating, and enhanced stratospheric water vapor.

We show that aerosol forcing exhibits a stronger surface temperature dependence than CO₂ forcing. Between 280 and 300 K, aerosol forcing becomes less negative with increasing surface temperature because its longwave component becomes increasingly positive. Additionally, the radiative feedback is less negative in the presence of the aerosol. Both the feedback’s dependence on aerosol concentration and the forcing’s dependence on temperature arise from aerosol absorption in optically thin spectral regions, which masks temperature-dependent surface emission.

This highlights the critical role of the spectral nature of aerosol longwave absorption in determining the surface temperature dependence of stratospheric sulfate forcing and in weakening radiative feedbacks compared to an atmosphere without stratospheric aerosol.