Heterogeneous chemical reactions between sulfate precursors on the surface of mineral dust aerosols affect the atmospheric aerosol cycle and the Earth radiation budget. Heterogeneous reactions of sulfur dioxide with mineral dust particles enhance sulfate formation by producing internally mixed sulfate dust aerosols. The anthropogenic sulfate forcing is estimated to be reduced to −0.18 W/m2 because of the reduced load of externally mixed sulfate aerosols, compared to −0.25 W/m2 when heterogeneous surface reactions are excluded. Sulfate coating on mineral dust particles increases wet deposition of dust, causing a positive anthropogenic forcing due to less sulfate coating at preindustrial times. However, heterogeneous reaction pathways are highly uncertain, which is reflected in the wide spread of reaction pathways and uptake probability coefficients in the literature. We undertake a series of sensitivity experiments with the Goddard Institute for Space Studies climate model to investigate the impact of the uncertainty in uptake mechanisms and dust aerosol size distributions on the simulated sulfate cycle. The results of this study are very sensitive to both tested variables. For example, doubling the clay emissions (particles whose radii are less than 1 μm) leads to a sevenfold increase in heterogeneous sulfate production.