<p>Cropland expansion has been the most notable change in global land use since industrialization. However, assessments of radiative forcing from land-use change have generally neglected the effects of cropland expansion on secondary organic aerosol. Here we perform a series of cropland expansion sensitivity experiments with an Earth system model that incorporates advanced secondary organic aerosol processes, including organic new particle formation. Our model results show an ~ 10% decrease in biogenic secondary organic aerosol burden due to cropland expansion since industrialization. This has reduced radiation scattering and cloud droplet formation associated with secondary organic aerosol, leading to a 146 ± 112 mW m⁻² decline in its radiative cooling forcing, equivalent to 8% of CO₂-induced radiative warming forcing since industrialization. The radiative impact is mainly attributed to the transition from evergreen and deciduous broadleaf forests to croplands. The radiative impacts are projected to increase by approximately 50% under future climate warming and reduced anthropogenic aerosol and precursor gas emissions, due to changes in biogenic emission intensity and background cloud condensation nuclei concentration. Policies addressing food security and climate change should account for the radiative impact of biogenic secondary organic aerosol from cropland expansion.</p>