I grew up on a farm in Idaho. And I spent my teenage years working with, wrestling with, and cursing irrigation. Irrigation is the lifeblood of farming in Idaho. I remember vividly a year when there was a drought, and the surface water dried up. I spent the hottest days of the summer laying 12-inch diameter aluminum pipe (hot!) from a groundwater pump to a surface-water pump because the surface water had dried up. That wasn’t fun. It was a lot of work in miserable conditions in an attempt to combat the heat.

Today in Illinois, where I now live, farmers are draining the rivers attempting to combat the heat with irrigation. They don’t have irrigation here normally because a drought like this is a once-in-fifty-years event. An irrigation system you turn on once every fifty years isn’t worthwhile.

So, when I hear people citing this year’s drought as an illustration of things to come because of global warming, I don’t think they know what they’re talking about. Farmers’ aren’t stupid. If it were like this every year, they would have irrigation. And things wouldn’t be as bad as they are.

But here’s the problem: most people didn’t grow up on a farm in Idaho. They don’t know what irrigation can do. And the worst part is that scientists, with their doomsday forecasts based on dumb-farmer models1, don’t know what irrigation can do. Or they don’t want to know.

Over at Greed, Green, and Grains my good friend and oft-times coauthor Michael Roberts reiterates a claim he has been making for quite some time:

Most commentators attribute this year’s bad crop progress with drought–a lack of rainfall. The problem with traditional drought measures is that they don’t predict crop outcomes especially well. Our measure of extreme heat–degree days above 29C–predicts crop outcomes a lot better.

Michael’s claim is based on a series of papers he has been working on with Wolfram Schlenker, et al. Their PNAS paper is the most widely cited in the series. For Michael, the coup de gras is this picture, which shows a sharp decline in crop yield above a certain (cummulative) temperature2.

What they don’t show you, but what is way more important, is this picture:3

The right-hand picture illustrates the main findings reported in the paper (for corn and soybeans). The left-hand picture illustrates the effect of heat when farmers are allowed to use irrigation.

This picture illustrates the difference precipitation makes. This picture shows the analysis west of the 100-degree meridian (on the left) along side the main analysis (on the right), which only uses data east of the 100-degree meridian. In the west, farmers respond to high temperature with irrigation. In the east, farmers rely  almost exclusively on rain. The picture shows that irrigation significantly dampens4 the effect of extreme temperature. In other words, heat doesn’t matter as much as long as there is precipitation. Or, more accurately, irrigation strongly mitigates the harmful effects of heat.

So, the consequences of global warming for U.S. agriculture won’t be nearly as bad as some people claim. Farmers are smart, and they will adapt.


1 A dumb-farmer model takes the present situation and extrapolates to the future without allowing farmers to adapt (by adopting irrigation, for instance).

2 Yes, I know it’s called ‘growing degree days’, but let’s avoid the jargon for a minute, shall we?

3 Yes, I know. It’s in the supplementary appendix. But it should be on the front page!

4 Sorry, I couldn’t resist.