The borders of the Corn Belt have always been fuzzy. The sprawling patchwork of cornfields that spreads across the Midwestern United States is one of the most productive agricultural regions on Earth. Over 36 percent of the world’s corn comes from the U.S., and almost all of that is grown in the handful of states nestled between the Great Plains to the west and the Appalachian Mountains to the east.

But the Corn Belt is on the move. Over the past couple of decades, farmland devoted to corn production has been creeping northwards and westwards. In North and South Dakota, grasslands that were formerly used for cattle grazing or set aside for conservation have been converted to cornfields. Between 2005 and 2021, the area of land harvested for corn in the U.S. increased by around 14 percent.

One of the big drivers of this shift has been bioethanol — transportation fuel usually made from fermented corn. Since 2005 the U.S. government’s Renewable Fuel Standard, or RFS, has mandated that gasoline producers blend corn ethanol into their fuel. The amount the RFS requires to be mixed in has ratcheted up each year from the policy’s start, and since 2016 gasoline producers have been instructed to blend 15 billion gallons of corn ethanol annually into transportation fuel. The RFS was supposed to reduce reliance on fuel imports and lessen the environmental impact of the transportation sector, but when it was introduced, some scientists warned that it might end up increasing overall emissions. Now it looks like those predictions have come to pass.

In February 2022, Tyler Lark, a scientist at the University of Wisconsin-Madison, published a study analyzing the impact of the RFS. Lark and his colleagues researched the impact that the policy had on crop prices and farm expansion between 2008 and 2016, comparing the real-world situation to a counterfactual one where biofuel production was kept at levels mandated in an earlier version of the RFS.

Lark’s study found that the RFS significantly pushed up the price of corn. This incentivized the expansion of total U.S. cropland by 2.1 million hectares between 2008 and 2016 — an increase of 2.4 percent. Often the areas newly converted to cropland were grasslands on the western edge of the Corn Belt. “Over millennia these grasslands have created really carbon-rich soils. And what happens is when you plow that up you expose a lot of it and make it vulnerable to being released into the atmosphere,” says Lark.

The supposed benefit of biofuel is that, although it still releases carbon dioxide when it burns, that carbon was drawn down from the atmosphere by the plants that make up the fuel rather than being released from oil that was once underground. But growing fuel creates emissions too. The biggest problem is when land that used to be a carbon sink is plowed up to plant crops, but manufacturing fertilizer is also a major source of emissions, and applying that fertilizer to land also releases greenhouse gasses in the form of nitrous oxide emissions.

In 2010 the Environmental Protection Agency, which sets the amount of corn ethanol required by the RFS, estimated that by 2022 corn ethanol would have total life-cycle emissions 20 percent lower than gasoline. But these projections didn’t account for the dramatic effect the RFS would have on land use in the US.

“I don’t think people expected as much land to come back into production,” says Lark. His study found that the RFS increased corn prices by 30 percent and the price of other crops by 20 percent. In response, farmers who previously used their land for cattle grazing or who were involved in conservation schemes started growing crops instead. All this land-use change has essentially outweighed the reductions in greenhouse gas emissions that come from growing fuel instead of pumping it out of oil wells.

Lark’s study comes at a decisive time for the future of corn ethanol. Later this year, the EPA will decide how much biofuel should be blended into U.S. transportation fuel from 2023 onwards. And on April 12 the White House temporarily waived the summertime ban on E15 — fuel made from gasoline blended with between 10.5 and 15 percent ethanol. In the U.S., E15 is banned over the summer months because of the way it reacts with sunlight to create smog, but lobbyists and some lawmakers have argued that removing the ban will ease the country’s reliance on Russian oil and keep down gasoline prices. Earlier this month, Congress voted to ban imports of oil, gas, and coal from Russia.

Increasing corn ethanol production would be a big mistake, says Jason Hill, a biofuels expert at the University of Minnesota. “The science has long pointed out that this is not where we want to go,” he says. “In the long run corn, ethanol has done almost nothing for our energy independence, and it has a large, disproportionately negative impact on the environment and food security.”

The projected impact of corn ethanol differs depending on how you estimate those emissions. In early April a group of U.S. senators representing Corn Belt states wrote a letter to the EPA urging it to adopt a model that shows biofuels have a considerably better environmental impact than Lark’s study suggests. But in March, Hill published an op-ed in the scientific journal PNAS calling for greater scrutiny of the models used by regulators like the EPA to assess biofuels. Lark’s study “supports other recent concerns that these commonly used models underestimate the emissions consequences of land-use change, which in turn leads to their overestimating the climate change benefits of corn ethanol,” Hill wrote.

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