emissions is uncertain. Here we investigate the sensitivity of future crop yield projections with a set of global gridded crop models for four major staple crops at 1.5°C and 2°C warming above pre-industrial levels, as well as at different CO2 levels determined by similar probabilities to lead to 1.5°C and 2°C, using climate forcing data from the Half a degree Additional warming, Prognosis and Projected Impacts (HAPPI) project. For the same CO2 forcing, we find consistent negative effects of half a degree warming on productivity in most world regions. Increasing CO2 concentrations consistent with these warming levels have potentially much stronger but highly uncertain effects than 0.5°C warming increments. Half a degree warming will also lead to more extreme low yields, in particular over tropical regions. Our results indicate that GMT change alone is insufficient to determine future impacts on crop productivity.