Noah S Diffenbaugh1,2, Marshall Burke3,4,5. 1. Department of Earth System Science, Stanford University, Stanford, CA 94305; diffenbaugh@stanford.edu. 2. Woods Institute for the Environment, Stanford University, Stanford, CA 94305. 3. Department of Earth System Science, Stanford University, Stanford, CA 94305. 4. Center on Food Security and the Environment, Stanford University, Stanford, CA 94305. 5. Environment and Energy Economics, National Bureau of Economic Research, Cambridge, MA 02138.