Moreover, there is the common claim that GMOs dramatically increase crop yields. That’s not very clear either. Sure, in many experimental plots and field trials, GMOs do seem to help crops get higher yield — mainly be reducing losses from weeds and insects — but this doesn’t always happen.

Why? We have to remember that GMOs in the field today are not revolutionizing the biology of plant growth or photosynthesis; they are simply replacing one kind of insect- or weed-control with another. Mostly, they have made crops taste nasty to bugs (Bt corn, for example) or make them resistant to industrial chemicals (glyphosate-resistant crops) that kill weeds, which should make it easier, cheaper, and more profitable for industrial-scale farms to manage their weed and insect problems.

However, despite the fact that experimental plots typically show that GMO crops end up with somewhat higher yields, this sometimes doesn’t translate to a real world impact.

For example, the observed, real-world GMO corn yields across the Midwestern United States (the heart of the biggest GMO corn belt on Earth) are almost identical to that of similar, non-GMO corn growing regions in Western Europe.

Observed yields (using five years of county-by-county data, from 2008–2012) for corn across the central United States (where GMO corn dominates) and district-by-district corn yield data from climatically-comparable regions of Western Europe (where GMOs are largely absent). This is essentially comparing real-world yields (not experimental plots) from Iowa and Illinois with regions in Western Europe (mostly France and the Netherlands) with the same climatic conditions — within the same range of rainfall and growing degree days. Data and graph courtesy of Jamie Gerber, University of Minnesosta.

This comparison looks at the yields of farms across the center of the US corn belt (using five years of county-by-county data) and compares them to distrtict-by-district yield data from regions of Western Europe (which, outside of Spain, do not grow much GMO corn) with identical climatic conditions. While experimental plots do often show some differences in yields due to the use of GMOs, at the end of the day, any boost in real-world yields are lost in the noise of the larger global food system.

This comparison is a simple-minded one, to be sure. It’s a bit of an “apples-to-oranges” comparison of looking at corn yields in the U.S. and Europe. And I acknowledge that, on carefully-controlled experimental plots, GM crops can often give higher yields. But my larger point is this: If GMO crops are so much more productive, than why don’t we see any difference between the world’s major corn growing regions — where one is dominated by GMO corn (the U.S.) and others are not?

The answer is simple: GMO corns doesn’t have that big an impact in the real world — as opposed to small experimental test plots — where other factors like soil management, real-world pest control techniques, and farmer behavior can make up for the differences.

Again, to be fair, some crops can show significant yield increases from using GMOs. And in theory — as shown by carefully-controled experimental field trials — you can for corn too. But for real-world corn, the largest GMO crop in the United States, you don’t see much of an actual difference. Otherwise, you’d see it in the global food production data between GMO and non-GMO corn-growing regions of the world. And you don’t.