Summaries of Observations

     This leads to this graphical interpretation.  Important caveats have to do with other limiting factors besides temperature - notably nitrogen and water, but also phosphorus, potassium, weeds, insects, soil carbon and acidity, etc.
    Yield responses, based on June temperatures (generally in the middle of the growing season) are shown for cities in the middle of the primary growing areas.

     Yields are sensitive to temperatures (and many other factors) in several months, not just June, as different events occur during the growing season.  But June temperatures are at least indicative.  Corresponding graphs for southern hemisphere growers (notably Brazil, Argentina, and Australia) would use December temperatures.

     Winter and spring wheat are both economically important in the US, India, China, etc.  An adaptation to warming already well under way is to plant winter wheat in Pakistan and northern India.  But even winter in Delhi is warm (mean temperature 60-65°F, much warmer than San Diego or San Antonio).

    The following can also be said, based on these and other studies.

Summary of Schlenker & Roberts' work.