Climate change increases the interannual variance of summer crop yields globally through changes in temperature and water supply.

Year-to-year variance of agricultural productivity is an important determinant of food security. Previous global analyses described increased yield volatility from warming, but it has become increasingly clear that changes in water availability are also a key determinant of yields. Here, we provide the first global quantification of climate change impacts on maize, soybean, and sorghum yield variance due to changes in temperature and soil moisture. Pairing an empirical crop model with CMIP6 simulations indicates that changes in temperature and soil moisture increase interannual weather-induced yield variance by [Formula: see text] across crops. This increase is driven roughly equally by previously quantified increased temperature stress variance, as well as by increased covariance between temperature and soil moisture stresses. Results using a simple land surface model are consistent with those using CMIP6 simulations in indicating that this increased covariance is driven by warmer air more quickly drying soils and by dry soils promoting greater warming.