Nonlinear Effects of Weather on Corn Yields*

This paper examines the reduced-form relationship between weather and yields using a unique data set of maize yields and daily weather records covering the eastern USA for 1950-2004. Since weather variations in a fixed location are exogenous and random, the reduced-form relationship constitutes a viable natural experiment and is therefore clearly identified. The study finds a significant nonlinear relationship between temperature and maize yields that is roughly in line with the concept of degree days: yields increase with temperature at moderate temperatures (between 12°C and 25°C), but rapidly become negative at temperatures in excess of 30°C.