Experts on Camera

Dr. Wolfram Schlenker: Rising temperatures and agriculture

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Extreme heat and drought are causing crop damage and losses for U.S. agriculture, with even greater impacts predicted for the future.

On August 19, 2021, SciLine interviewed: Dr. Wolfram Schlenker, a professor of economics at the School of International and Public Affairs at Columbia University, where he studies the effects of weather and climate on agricultural yields and commodity prices. See the footage and transcript from the interview below, or select ‘Contents’ on the left to skip to specific questions.

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WOLFRAM SCHLENKER: My name is Wolfram Schlenker. I’m a professor at the School of International and Public Affairs and the Earth Institute at Columbia University.

Interview with SciLine

How is climate change – and in particular, extreme heat – affecting farmland and crop yields in the United States?


WOLFRAM SCHLENKER: So when you hear climate forecast, you often hear, like, a predicted increase in average temperature by – you know, we’ve been trying to keep it under 2 degrees C under Paris or 1 1/2 degree. So we often talk about the average. But then when you think about crop yields, what really matters is not just the average temperature, but especially the temperature extremes. So we’ve all heard about freezes killing, like, crops initially, but when we did a lot of statistical analysis, we also found that extreme heat is actually a really strong driver of crop yields.

So you can think about it that for – we look at, specifically, corn, soybeans and cotton in the United States. And corn and soybeans are two staple commodities that’s sort of very important for human calorie consumption. Just four crops – corn, soybeans, wheat and rice – together account for about 75% of the calories that we consume. And so we focus on those two – corn and soybeans. And there, we find that a temperature of roughly around 84, 86 degrees F is best. It seems to be best for, like, increasing yields. If you’re colder, it sort of decreases your yields. If you’re hotter, it decreases your yields.

But there’s a huge asymmetry in there, meaning that if you’re above this 84, 86, you’re much worse off than if you’re by the same amount below. So for example, if you go from 84 to 90, which would be six extra, you will be giving about 10 times as much of a damage as if you go 10 below, so from 84 to, like, 78.

What do you make of reports that claim that climate change may be beneficial for certain crop yields in some places?


WOLFRAM SCHLENKER: I’m originally from Germany. And here, you can really see that the quality of the wines have actually increased over the last couple of years because we’ve been sort of at a northern edge where you can grow wine. And I – through climate change, it seems to actually have been beneficial for vineyards. That’s, I would say, though, the minority of crops. So especially the big commodity crops – again, that’s corn, wheat, rice and soybeans – that’s predicted to be significantly negatively impacted from rising temperatures.

What is the relationship between climate change and commodity prices?


WOLFRAM SCHLENKER: So for commodity prices, what matters is also, like, the aggregate supply all around the world. So, you know, there’s this famous conundrum in the United States that sometimes you have a freeze in Florida for the orange crop and it’s actually one of the most profitable year for orange farmers. The reason for that is that the profit of the farmer is sort of a product of the yield; how much they actually produced – the quantity – and the price they get for it. And if a country is a pretty big producer of a particular commodity, if that commodity becomes short in supply, you sometimes have a very large price swing to basically balance supply and demand again. So there’s this sort of sometimes counterintuitive effect that we observe that when the yield actually goes down, the profits of farmers can go up. And that’s because the prices more than offset the decrease in the quantity.

Now that’s mostly in the short term. Obviously, if the orange crop in Florida were to be permanently lowered, people might start growing oranges somewhere else, and so the price effect might be less. But there is sort of this idea, especially with the United States being by far the biggest producer of commodity crops, that anything that happens in the United States has big repercussions for the world’s food prices.

So we often think about Saudi Arabia as being a dominant player in the oil market. The United States is actually a bigger player in the pure caloric commodity market. As I mentioned earlier, wheat, rice, soybeans and corn account for about 75% of the calories that humans consume either directly by eating it or indirectly because they’re used as feedstock for, like, animals. And of those four commodities, the United States market share is about 25%. That’s more than twice as much as Saudi Arabia’s market share for oil. So in that sense, anything that happens with weather in the United States directly translates into international commodity prices.

How have farmers adapted to the changing climate?


WOLFRAM SCHLENKER: That’s a very active area of research, and so people sort of disagree a bit. On the one hand, we see, for example, that crops have been moving – where they’ve been grown. We see that corn has been growing further north than it used to have been. But it’s not only because of warming trends, but also because we have shorter-season varieties that we didn’t used to have. But you now see corn in Minnesota that they didn’t used to see many years back.

On the other hand, they’ve also adopted more irrigation in some areas. Now, in some areas, they’ve been irrigating so much that they’re starting to run out of water. So sometimes you can adapt sort of in the short term for a couple of years, but then once you continue doing this, you actually start running into problems because you deplete the aquifer.

Now one problem that keeps farmers from adapting is that we have subsidized crop insurance. So farmers in a way are – like anybody who is insured against losses, don’t necessarily have the full incentive to do everything they can to counterbalance a negative weather shock because they sort of get bailed out at the end. So some studies claim that sort of that limited the amount of adaptation that farmers could engage in.

Do you have any predictions for the future of agriculture as greenhouse gas emissions continue?


WOLFRAM SCHLENKER: So my personal prediction specifically for the United States now is that we are going to see something that’s a bit analogous to what we’ve seen in New Orleans with the flooding. So, you know, we see that things are getting worse. Like, you know, New Orleans was sinking, so they’re building higher dams. And that sort of protects us in the short term, but eventually, it sort of starts rising and rising – the water level – and we had something like Katrina, and then it flips over the dam and sort of we have this catastrophic effect.

So let me bring this back into the agricultural example. There’s actually a bit of a puzzle because while the climate models have been very good at predicting increases in average temperature and increases in temperatures over cities, the corn belt has not warmed as much as predicted in some of the climate models. And specifically, extreme temperature – that I’ve emphasized is very detrimental to crop yields – has not gone up as much as what climate models originally predicted. And one explanation that a couple of papers have put forward is that through intensification of agriculture and especially through additional irrigation, you get a bit of a negative feedback loop, maybe actually lead to a little bit of a cooling that sort of limits how much extreme temperatures you can have.

So I think we might not see too much for the next decade or two, but that eventually, as farming land starts to get abandoned, you might actually see pretty rapid increases in extreme temperatures and farm abandonment. That would be, right now, my best guess.

There’s growing public attention to the fact that OSHA doesn’t have federal standards to protect farmworkers from extreme heat. As heat waves get more intense, risks to farmworkers will worsen. How might this trend affect farming?


WOLFRAM SCHLENKER: So there was a really interesting paper that some of my colleagues at Columbia did. They got data on pickers in orchards in California. And they found that both pollution and temperature actually impacts the amount because they’re paid on a piece rate, so they could really detect how much they pick because it impacts their pay. And both higher pollution level as well as higher temperatures lower the productivities of pickers. So that’s one example of a farmworker. So there will be actually a strong labor effect from extreme heat not just directly on the crop, but also on the farmworkers picking the crop.

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