Response to Schlenker and Roberts’ Study of US Crop Yields under Climate Change

In response to Schlenker and Roberts’ article Nonlinear temperature effects indicate severe damages to U.S. crop yields under climate change, which indicated that temperature increases will severely damage US crop yields in the next century Meerburg et al. (2009) challenged the paper. Meerburg et al’s article Do nonlinear temperature effects indicate severe damages to US crop yields under climate change states that in fact the Schlenker and Roberts article is erroneous, and that it was a pessimistic view of the issue. Hannah Carr
Meerburg, G., Verhagen, A., Jongschaap, R., Franke, Schaap, B., Dueck, T., van der Werf, A. 2009. Do nonlinear temperature effects indicate severe damages to US crop yields under climate change? PNAS 106, 120–120.

The study by Meerburg et al. states that high temperatures have different effects on plants at different developmental stages and are not always problematic. They used Brazil as an example of temperature having little to no effect on crop yield. The article states that Brazilian farmers successfully increased the productivity of soybeans, maize, and cotton in the last decade despite the fact that the cumulative days of exposure to temperatures above the threshold values is far greater than in the US. The state of Mato Grosso, Brazil exceeds 35 °C for 118 days per year, 75 of those days being in the average soybean-growing season and the production of soybeans was approximately 3.1 tons ha-1 yr -1 in 2008, exceeding that of the 2008 US crop yield. Similarly the cotton yield of Brazil in 2006/2007 was 1.4 ton ha-1 yr-1 compared to the US’s .9 ha-1 yr-1. With these two examples the authors concluded that despite relatively long periods of exposure to high temperatures, Brazilian farmers have managed to boost crop productivity.
With the challenge at hand, Schlenker and Roberts reply, stating that Meerburg et al’s. information is misleading because some areas of the United States have much greater exposure to extreme heat than Mato Grasso and vice versa. The authors contrast Mato Grosso to Illinois, which is one of the most productive states in the United States. The average daily summer temperatures of Mato Grosso are in fact higher than in Illinois, however after a satellite scan of the region it reveals that there are in fact no soybeans growing in the hotter area. If the maximum temperatures are averaged over the region that soybeans are actually grown in the average exposure to degree-days less than 30 °C in Mato Grosso, similar to the southern half of Illinois. Therefore, the authors state that there is no contradiction between crop yields in Mato Grosso and the earlier findings in the United States.

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