How Corn Ethanol for Biofuel Fed Climate Change | Civil Eats

How Corn Ethanol for Biofuel Fed Climate Change

The Renewable Fuel Standard promised to pay farmers to fight climate change and boost U.S. energy independence. Instead, a new five-year study of its impact on land use suggests it led to increased fertilizer use, water pollution, and likely at least 24 percent more emissions than gasoline.

Harvesting corn at Estrem Farms in Nerstrand, Minnesota.

The U.S. is the world leader in biofuel production—generating 47 percent of global output over the last decade. The ten-fold expansion in ethanol production in the U.S. from 2002 to 2019 has been driven by the Renewable Fuel Standard (RFS), a federal program that since 2005 has required transportation fuel to contain a minimum volume of renewable fuels. So far, that has largely meant corn ethanol. Currently 98 percent of gasoline in the U.S. contains some ethanol, most commonly 10 percent, or E10.

For the last decade, ethanol has helped keep corn in high demand, and made it the most-planted U.S. crop. In fact, roughly 40 percent of all corn is now used to make ethanol. Meanwhile, the number of corn farms over 500 acres in size has increased over time, while the number of small corn farms is dwindling. And all this growth has led to record profits for the companies that buy and sell the nation’s corn. For instance, last month, Archer-Daniels-Midland, the food processing and commodities trading giant, reported its highest-ever earnings, a net income of over $2.7 billion, due in large part to rising biofuel demand.

For the last decade, ethanol has helped keep corn in high demand, and made it the most-planted U.S. crop. In fact, roughly 40 percent of all corn is now used to make ethanol.

Despite the promise that the RFS would reduce greenhouse gas emissions, a new study published in the journal Proceedings of the National Academy of Science (PNAS) today finds that expansion of U.S. corn cultivation has come at eye-popping environmental costs. Corn production expanded by 8.7 percent, or 2.8 million hectares (6.9 million acres), between 2008 and 2016. As a result, the researchers found that nationwide annual fertilizer use surged by 3 to 8 percent and water pollutants rose by 3 to 5 percent. The sheer extent of domestic land use change, however, generated greenhouse gas emissions that are, at best, equivalent to those caused by gasoline use—and likely at least 24 percent higher.

That’s because the RFS caused corn prices to spike by 30 percent and soybean and other crops by 20 percent. As a result, farmers planted corn everywhere they could, replacing other crops and pastureland, and plowing up land that had previously been reserved for conservation purposes. They also often skipped the soybeans in their rotations, despite the potential impacts on their soil.

Tyler Lark, who studies land use change at the University of Wisconsin at Madison, has been tracking cropland expansion for years, but the burning research question in his field has been: To what degree have biofuels driven that expansion? Lark teamed up with agricultural economists and water quality experts for five years to produce what is one of the most comprehensive studies to date.

The bottom line is bluntly straightforward. “If you crank up demand, you get land use change,” says Lark, who is also a co-author of the new study. Every major agency in the U.S. that puts out data, including the U.S. Department of Agriculture (USDA), the U.S. Geological Survey (USGS), and the Environmental Protection Agency (EPA) have all observed this rapid cropland expansion, adds Lark.

Previous studies, however, dramatically underestimated the impacts those land use changes had on carbon emissions; in fact, the models treated the land that was converted from conservation or pasture as if there was little change in the amount of carbon stored once it was planted with corn—which runs counter to existing empirical evidence.

The new study comes at a crucial moment. This year, the Biden administration will reset the biofuel volume targets of the RFS, and it’s yet to be seen how new targets could ultimately impact the price of corn, demand for soybeans to make biodiesel, the farms that produce these crops, and—ultimately—the dead zone in the Gulf of Mexico.

Plowing up Carbon

Lark’s findings are the latest evaluation of the hotly contested biofuel carbon footprint. Several disparate data sources have confirmed the overall trend of grassland-to-cropland conversion in recent years, but researchers have used many different methodologies and assumptions to analyze that footprint over the years, leading to divergent estimates of greenhouse gas emissions resulting from the RFS.

The current study used the survey-based USDA National Resources Inventory (NRI), which had been endorsed previously by the Renewable Fuels Association, a trade association for the ethanol industry, to quantify cropland expansion area and the portion attributable to corn ethanol. Still, the organization criticized the findings.

“The claims in this report simply don’t align with reality and the facts on the ground. By slapping together a series of worst-case assumptions, cherry-picked data, and disparate results from previously debunked studies, the authors created a completely fictional and erroneous account of the environmental impacts of the Renewable Fuel Standard,” said Geoff Cooper, president and CEO of the Renewable Fuels Association in the statement responding to the study. (Requests for comment from the National Corn Growers Association and the Iowa Renewable Fuels Association were not returned.)

The Conservation Reserve Program (CRP), which pays farmers to keep some of their land uncultivated, saw the acreage in the program decrease precipitously after 2007 as farmers capitalized on high corn prices. The CRP is now at its lowest enrollment in over 30 years.

Given the differing estimates of greenhouse gas impacts, Jeremy Martin, director of fuels policy at the Union of Concerned Scientists (UCS), doesn’t think asking whether corn ethanol is better or worse than gasoline is the most important question. “I don’t think that biofuels are going to go away. But clearly they’ve had an impact on water quality and fertilizer usage—which are important findings to consider when setting future biofuels policies,” he says. He suggests a more relevant question is: How many acres of corn can farms plant while still meeting water quality or conservation goals?

The federal Conservation Reserve Program (CRP), which pays farmers to keep some of their land uncultivated, saw the acreage in the program decrease precipitously after 2007 as farmers chose to capitalize on high corn prices. As a result, the carbon storage gained via the CRP was lost to the atmosphere. And now, the CRP is at its lowest enrollment in over 30 years—while the USDA just announced it plans to spend $1 billion to encourage carbon sequestration in soil.

Image courtesy of Silvia Secchi. Read about the difference between Conservation Reserve Program (CRP) enrollment and general CRP enrollment.

Image courtesy of Silvia Secchi. Read about the difference between Conservation Reserve Program (CRP) enrollment and general CRP enrollment.

Ethanol critics say this study suggests what some have long suspected—that the RFS is a tool to prop up corn prices. “If this paper is discounted [in RFS deliberations], or we fail to acknowledge the net greenhouse gas effect of corn ethanol, we will be admitting this policy is all about income support for farmers,” says Silvia Secchi, a natural resource economist at the University of Iowa.

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Secchi says 15 years ago, corn ethanol was touted as a means to energy independence as well as a climate change mitigation strategy. “But the U.S. is effectively energy independent with fracking, so that’s out the window,” she said. “The second argument—that it would reduce net greenhouse gas emissions—is destroyed by this paper.”

In addition to its role as a force for change for Corn Belt farms, ethanol has also become a cornerstone of Midwest politics. With 42 ethanol plants, Iowa is the nation’s biggest producer of both corn and ethanol. Political support for biofuels inevitably cites the industry’s economic importance to the region, and its role in keeping rural economies afloat.

Some say the numbers behind that narrative are routinely overinflated, however. The latest renewable fuels industry estimates claim 46,000 jobs through the Iowa economy, but Iowa State University economist Dave Swenson says he can only find around 7,200 jobs. By Swenson’s calculation, counties with ethanol plants actually averaged larger population declines, grew merely 0.2 percent more as measured by wage and salary jobs, and had a higher rate of farm proprietor decline. “Ethanol has not been any sort of a game changer for rural Iowa’s overall economies or their demographics,” says Swenson.

Corn’s Impacts Are Visible in the Gulf

The downstream costs of expanded corn production are increasingly difficult to ignore.

According to the new study, the states with the largest expansion of corn cultivation, between 50 to 100 percent, were North and South Dakota, western Minnesota, and other states further to the south in the Mississippi alluvial plain. The increased fertilizer use caused by more corn acres likely contributes to the nutrient pollution that causes the annual dead zone in the Gulf of Mexico. In 2021, more than 6,300 square miles of Gulf Coast waters, the equivalent of more than 4 million acres of fish habitat, were starved of oxygen—over three times larger than the 2035 target set by the task force working to shrink the dead zone.

In another example of this trend, the state of Illinois—where farmers planted 11 million acres of corn in 2020—aimed to reduce nitrates and nitrogen by 15 percent and phosphorus by 25 percent by 2025, but a recent report indicates that nitrogen loss actually increased by 13 percent and phosphorus losses increased by 35 percent during that time, as farmers planted an unprecedented number of corn acres.

“In places like Iowa, where farmers typically rotated corn and soybeans, we see a lot more continuous corn or three-year rotations of corn, corn, soybean,” says Secchi. She has also pointed to the fact that Iowa farmers receive the most federal subsidies in the country, meaning that taxpayers are essentially paying farmers to continue and expand practices that reduce soil health, maintain a dead zone that costs $2.4 billion in disrupted fisheries and damaged marine habitat, and at best generate the same carbon emissions as gasoline.

‘Fueling Jets with Vegetable Oil Is Even Worse Than Fueling Cars’

In 2008, contrary to EPA models suggesting otherwise, Timothy Searchinger, a senior researcher at Princeton University’s Center for Policy Research on Energy and the Environment, was one of several who predicted that using U.S. croplands for biofuels would increase greenhouse gas emissions through land use change. Now, his assessment has been validated by the new study. Searchinger says the new study boils down to a simple, inescapable truth: Using land has a cost. And some uses simply don’t make sense because the cost is too high.

“It’s crazy to use this very limited resource—highly productive land—for energy,” he said. “It’s almost spectacularly inefficient.” Corn ethanol converts 0.15 percent of solar energy into usable energy, while a solar cell today converts 15 to 20 percent of sunlight to energy. “And the good news is you don’t need to put a solar cell on the best available farmland.”

The fact that the study only focuses on greenhouse gas emissions within the U.S., likely reveals only a fraction of the impact. “The international effects are undoubtedly larger than the domestic effects,” says Searchinger.

“It’s crazy to use this very limited resource—highly productive land—for energy. It’s almost spectacularly inefficient.”

Secchi says corn isn’t like other crops. Agricultural innovations over the last century have led to a system that produces so much of it that the agriculture industry has often found itself manufacturing demand to meet the supply. “It’s time to factor in the broader impacts of creating that demand,” she adds.

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“We currently use over one-third of the corn we produce for biofuel, and it offsets 6 percent of gas use. We could get the same benefit by increasing fuel economy of cars from 22 to 24 miles per gallon,” says Jason Hill, a bioenergy researcher at the University of Minnesota.

Although the RFS targets have had an important impact on corn production in the past, it’s not clear whether they will be an important lever going forward. “Right now, corn ethanol consumption isn’t even meeting the targets of the RFS, but even if you got rid of these policies, you probably wouldn’t sell substantially less ethanol (than the current 10 percent blending rate),” said Union of Concerned Scientists’ Martin. (That said, the Iowa governor is pushing legislation that would require the state’s gas stations to have at least one pump at each station carry E15, a 15 percent ethanol blending rate.)

At the same time, the efficiency of electric vehicles is also expected to complicate the future demand for ethanol. And with this in mind, the budding biofuel industry is turning its attention to vegetable oil production to make other fuels.

“Post-2022 RFS targets are very unlikely to lead to dramatic increases in ethanol use. In the last decade, RFS policy has had a much more dramatic effect on the use of vegetable oil-based fuels, especially biodiesel” says Martin. “And looking forward, renewable diesel and sustainable aviation fuel could add substantially to the use of vegetable oil for fuel.”

That shift could create a similar—and likely more devastating—impact. Fueling jets with vegetable oil is an even worse idea than fueling cars, says Searchinger. Oil production requires even more land than starches do and new sources of vegetable oil would likely cause soybean and palm oil expansion in the tropics. “You could have staggering environmental effects if, for example, half of the aviation fuel is supposed to come from biofuels by 2050,” he explains.

Either way, it’s clear that the RFS presents an important crossroads for the future of biofuel production—and the land on which it is farmed. As study co-author Lark put it: “Decisions made this year have the potential to impact our climate and landscape for decades to come.”

Virginia Gewin is a freelance science journalist who covers how humans are profoundly altering the environment – from climate change to biodiversity loss – and undertaking extraordinary endeavors to preserve nature. Her work has appeared in Nature, Popular Science, Scientific American, The Atlantic, Bloomberg, bioGraphic, Discover, Science, Washington Post, Civil Eats, Ensia, Yale e360, Modern Farmer, Portland Monthly and many others. Read more >

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  1. Virginia, thank you thank you. Much needed. The other major impacts are water infiltration and soil biology that is devastated by corn culture (the way we do it). This impacts water cycle, weather!!!, flooding and means that our most fertile soils (states worth) have become more impenetrable that macadam. Weeds grow up through macadam but not in our bread basket. A simple policy changes if a few dollars subsidy taken from corn and given to grass would change things dramatically because farmers do farm the farm bill subsidies.
    Carry on your good work.
  2. Anita Richert
    CRP has declined not because of ethanol demanding corn but because the government cut the rates and programs. If there was a CRP program for you to turn off your computer to save energy for an hour a day and you are a lawyer making $500/hour and the CRP would pay $100 to you for your sacrifice, you may sign up. If the CRP said they would pay nothing how many takers would you get? This is not an ethanol problem. We need to look at the real problem and that is big polluters in the form of manufacturing and urban lawn maintenance. Most of the pollution in the Mississippi River comes from urban sources. There are been scientific studies proving it. Farmers are not going to put on excess nitrogen and other fertilizer, it is far too expensive to just wash down the waterway. Farmers put the fertilizer exactly where the growing crop can access it and use it. Have you ever seen a lawn care application in your neighborhood? They spread the fertilizer and herbicide over the top of the lawn and it goes everywhere, sidewalk street, driveway. Do you think that nitrogen is going to soak into the driveway or street? When a farmer applies nitrogen it goes into the soil right next to the door zone and not a drop goes on the road. I appreciate your effort to find a solution to a real problem we have however don't just blame the farmers because of an apparent relationship of less CRP/more pollution. There are more moving parts to this complex issue than the simple fix of blame the farmer.
    • Doug Gurian-Sherman
      Sorry Anita, but what you say is bunk. There are many studies over the years that show that corn is by far the biggest contributor to nitrate in surface and ground water in the US Midwest (and elsewhere), and dead zones. These have often involved actual measurement of nitrogen in streams throughout the region where the sources can be directly mapped. CAFO manure is also a major source, and they are fed by corn and soy. Tile drainage systems, pervasive in the Midwest, also facilitate the loss of nitrogen from crop fields. Direct measurements show that corn often only captures 40 to 50% of applied nitrogen, even when it is not overapplied. Precision application (when it is used) can help, but not nearly enough.

      And this article does not even get into the huge biodiversity harms caused by corn and beans (and other) monocultures or bicultures, and their heavy dependence on pesticides and lack of diverse habitat.

      But you are right that farmers are not the primary culprits, but rather the large companies like Cargill, JPS, ADM, Monsanto/Bayer, and retailers like Walmart, etc. and the harmful policies and economic incentives they drive that are the real causes. Farmers are mostly caught in the middle. Often they struggle with overproduction and subsequent prices below the cost of production.

      However, farmers ultimately contribute to the problem with defensive statements that ignore or distort the science, whether about nitrogen fertilizer (and phosphorus) and water pollution or climate change. Those farmers, allied with others, could be a force for positive change. But instead, the big companies, that have been making excessive profits at their expense, are laughing all the way to the bank.

      We need fundamental change in how we farm, based on agroecology and food sovereignty, that supports and works for farmers, rural communities that are also hurting, and the environment and eaters. Farmers could be a real voice for that change, but often instead let the big corporations direct the agenda to their own (and everyone else's) long-term detriment.
  3. The common cat tail reed(Typha) produces 8 to 10 fold the amount of carbohydrates(starch) than conventional corn crops per acre.
    Because Typha is classified as one of the most obnoxious weeds known to agriculture, agricultural runoff carefully furrowed to drain into acreage planted with the cat tail reed would be almost too much, making water and fertilizer inputs unnecessary.
    Along with economic amounts of starch for ethanol production, downstream issues of toxic algae outbreaks and oxygen dead zones in the Gulf of Mexico would be resolved.
  4. Greg Fynboh
    Without the benefit of money from the oil industry to do a study "proving" otherwise, it doesn't make any sense that ethanol pollutes more than gasoline.
    Government ag policy could be much improved to encourage (or, God forbid, mandate) conservation measures and regenerative farming. Corn production would still occur with good farm policy. Just doing a smell test, ethanol is not polluting more than gasoline or any part of the fossil fuel industry including electricity generated from coal or natural gas and minerals mined for batteries with diesel powered equipment. I empathize with the sentiment that we are not doing the climate any favors by how we live but let's prioritize the problems properly. The oil industry is at the top of the bad problem list. Even without another sponsored study that computes.
  5. Paul swinand
    I am curious if anyone has asked the question if we could ever plant enough more corn to make a dent in demand for petro-based fuels? If corn ethanol is roughly 2% of total US energy (source:, and per your stat 40% of corn is being used for fuel production already, mathematically a 5x increase in corn planting would be needed to reach just 10% of total US energy needs (at the same avg. efficiency of production.) Corn production would thus be 260% of today's levels; is anything close to this possible? (I read we increased planting 8% from 2006 to 2016, by comparison).

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