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How Climate Change Is Making America’s Favorite Crop More Vulnerable

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"How Climate Change Is Making America’s Favorite Crop More Vulnerable"

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The impacts of drought on a corn field.

The impacts of drought on a corn field.

CREDIT: Shutterstock

In America, corn is everything. It’s in our foods — meat, cheese, milk, ketchup, salad dressing, soda, cookies, and chips. It’s found in our makeup, toothpaste, and perfume. Corn even powers our cars, with roughly 40 percent of U.S. corn production used to make ethanol.

But corn production in the American Midwest is becoming more and more vulnerable to the effects of man-made global warming, raising questions about the crop’s future viability, according to a study published Friday in the journal Science. Extreme heat and drought, the study said, has been gradually causing higher stress among densely-planted corn, slowly impacting traditionally increasing crop yields.

“The Corn Belt is phenomenally productive,” lead researcher David Lobell, an associate professor of environmental Earth system science at Stanford University, said. “But in the past two decades we saw very small yield gains in non-irrigated corn under the hottest conditions. This suggests farmers may be pushing the limits of what’s possible under these conditions.”

Though large decreases aren’t being seen now, the study predicted troubling decreases if the plants can’t learn to adapt to drier and hotter conditions. Currently, the United States produces 40 percent of the world’s corn.

If they stay as sensitive as they are now, corn crops in the United States could lose 15 percent of their yield within 50 years. If they continue the trend of becoming more sensitive over time, they could lose as much as 30 percent.

In order to come to that conclusion, Lobell and scientists from the University of Hawaii analyzed both crop yield data from the U.S. Department of Agriculture and high-resolution daily weather data. Using that, they found that corn crops have been becoming more sensitive to daytime vapor pressure deficit (VDP), a measurement of the amount of moisture in the air. VDP is key to figuring out aridity — a key indicator of drought, the study said.

“The data clearly indicate that drought stress for corn … comes partly from low rain, but even more so from hot and dry air,” Lobell, also a lead author for a chapter in the U.N. Intergovernmental Panel on Climate Change (IPCC) Fifth Assessment Report, said.

The IPCC’s latest report, a conservative panel which draws from the expertise of more than 800 scientists around the world, said it is “more likely than not” that man-made global warming is causing longer and more intense droughts in many regions, including the American Midwest. Climate change has also been shown to worsen Western droughts, even if it doesn’t reduce precipitation.

It’s been known for some time that corn is sensitive to temperature increases. The big question, though, is whether there would be ways to have corn plants adapt.

Over the last few decades, the study said, corn in the United States has been enhanced to have built-in pest resistance, and more water-absorbent roots. This has allowed farmers to plant seeds closer together, making a denser corn field with large yields.

Lobell’s study suggests that the highest heat- and drought-induced stress on corn has been in these densely-planted fields, which is the reason why yields have not been as high as before. To solve this, Lobell said, farmers might have to stop planting their corn so densely, rather than trying to manipulate the plant to adapt to climate change further.

“The adaptation challenge is maybe even harder than we thought. It doesn’t say it’s impossible, but it’s going to require a lot of effort,” he said. “There’s only so much a plant can do when it is hot and dry.”

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