The land used growing corn-based ethanol that has long been put into fuel for automobiles may be doing more harm than good to the environment. That’s according to a new study published in the Proceedings of the National Academy of Sciences.

The study, commissioned by the U.S. Department of Agriculture, contradicts previous research commissioned by the department that showed that ethanol was greener than gasoline. The new research suggests that ethanol is likely 24 percent more carbon-intensive than gasoline.

“Corn ethanol is not a climate-friendly fuel,” Dr. Tyler Lark, an assistant scientist at the University of Wisconsin-Madison Center for Sustainability and the Global Environment, and the lead author of the study told Reuters.

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A 2019 study from the USDA found that, because of the carbon sequestration associated with planting new crops, ethanol is 39 percent less carbon-intensive than straight gasoline. Lark, however, says that previous research underestimated the emissions impact of land conversion.

Tilling fields releases carbon stored in the soil and other farming activities, such as applying nitrogen fertilizers, also produce emissions. There is also a cost to processing and combusting the ethanol, all of which combines to make ethanol dirtier than normal fuel, the study suggests.

Geoff Cooper, the president of the Renewable Fuels Association, a leading trade association in the American ethanol industry, told Reuters that the study was “completely fictional and erroneous,” claiming that it made “worst-case assumptions.”

America’s oil refiners are currently required to mix around 15 billion gallons of ethanol into the nation’s gas every year as a result of 2005’s U.S. Renewable Fuel Standard law, which was introduced to reduce emissions, support farmers, and cut U.S. dependence on energy imports.

That law set standards until 2022 and now the Environmental Protection Agency is looking at its biofuel policy and considering changes to the program. The agency plans to propose 2023 requirements in May. President Biden, meanwhile, is looking to review biofuel policies as part of a broader effort to decarbonize the U.S.