<p>Mineral dust aerosols affect Earth’s energy balance in multiple ways, including interactions with solar radiation, but this effect remains poorly quantified. A central limitation has been the lack of reliable global information on dust mineral composition, particularly light-absorbing iron oxides. An imaging spectrometer, placed aboard the International Space Station by the Earth Surface Mineral Dust Source Investigation mission, provides high-resolution, near-global retrievals of surface mineralogy. Here we incorporate these retrievals into four Earth system models to constrain the dust shortwave direct radiative effect. Analysis shows that the retrievals reduce the radiative effect uncertainty by more than a factor of six in both present-day (2007–2011) and late twenty-first-century (2090–2094) climates. This improvement is enabled by tighter constraints on iron oxide content, which reduce its uncertainty contribution from 0.62 W m⁻² to 0.10 W m⁻². Greatest improvement occurs over the Sahara, where high dust abundance and surface reflectance amplify the influence of iron oxides. Orbital spectroscopy thus shifts the primary uncertainty from mineral composition to processes controlling the spatial distribution of dust. These findings mark a transition towards confident aerosol composition modelling and provide an improved basis for assessing how dust alters Earth’s energy balance today and in a warming future.</p>