Evolution of heat tolerance in corn: implications for climate change

I've just finished my lastest paper with Wolfram Schlenker.  It will be a chapter in a book "Climate Change: Past and Present" that will be published by the National Bureau of Economic Research.  Here's a link to the draft we're shipping off, and the abstract is below.
We present new evidence on the relationship between weather and corn yields in Indiana between 1901 and 2005, extending earlier results for corn from 1950-2005. Indiana, a major corn-producing state has the best coverage of daily weather records for the early half of the 20th century. The effects of precipitation and extreme heat are shown to evolve over time as new seed varieties, supplemental irrigation systems and management practices are introduced. In particular, we find the detrimental effects of either too much or too little precipitation seems to have steadily diminished over time. In contrast, the evolution of tolerance to extreme heat is highly nonlinear, growing with the adoption of double-cross hybrid corn in the 1940’s, peaking around 1960, and then declined sharply as single-cross hybrids came online. Corn in Indiana is most sensitive to extreme temperatures at the end of our sample. Since climate change models predict an increase in extreme temperatures, the big question is whether the next breeding cycles can increase both average yields and heat tolerance simultaneously as in the period 1940-1960, or whether an continued increase in average yields can only be achieved at the expense of more sensitivity to extreme heat as in the period from 1960 onwards. Finally, we discuss these impacts in relation to possible distortionary effects of current agricultural subsidies in the United States.
We take a few digs at Michael Pollan in the later part of the paper.  Like I've said before, I like Pollan's books and highly recommend them.  But he steps in a few places he maybe shouldn't and this leads to popular ideas that are badly wrong headed.  In fact, this whole section doesn't really fit with the rest of paper, but we had to include it because of all the suggestions that climate change impacts on corn production were a GOOD thing, since corn is so evil anyway.

Yeah, the meat industry and corn syrup is pretty disgusting.  But no, huge hits to corn yields are unlikely to make us less fat.  It will just make the poorest in the world disappear, and that's definitely not good.

I have a twinge of regret with this paper.  I like the paper a lot and am happy to publish with NBER amid the company of some excellent scholars.  My regret comes from the fact that book chapters count for little at tenure time and think this could have flown higher.  C'est la vie.

Update: Many thanks to Andrew Leonard for summarizing this research on his "How the World Works" blog at Salon.com


  1. Have you looked at the corn yields in Indiana based on conventional vs organic methods?

    Organic production is more stable over various weather cycles.

  2. Anonymous: Thanks for your comment. There's nowhere near enough data to look at organic separately. We need LOTS of it to do this kind of analysis.

    I suspect it has more to do with the cultivar than how the crop is managed.


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