WILLIAM RAU

As the century opened, ethanol entered the stage as a so-called cleaner alternative to gasoline. If a Model T could run on moonshine, then flex-fuel cars could run on 100% ethanol — and were (Voelker 2014). However, instead of a substitute for gas in the U.S., it became an octane booster and gasoline additive. The U.S. Renewable Fuel Standard (RFS) spurred this application by mandating sale of 36 billion gallons of renewable fuel containing at least 20% less carbon than gasoline. Analysis showed that ethanol met the 20% reduction, just barely. Hence, it was the RFS that stimulated the large-scale expansion of corn ethanol because nearly all 135 billion gallons of gasoline we burned in 2022 contained a mix of about 10% ethanol.

HERE’S THE PROBLEM: Research by Tyler Lark et al. (2021), published in the Proceedings of the National Academy of Sciences, found that the carbon intensity of corn ethanol to be 24% higher than gasoline. In a classic instance of unanticipated consequences, expansion of land use for corn production increased the overall carbon emissions of corn farming to the point that corn ethanol no longer meets the carbon reduction standard of the RFS. It’s not even close.

Even with substantial expansion and intensification of corn production, ethanol gobbles up one-third of the U.S. corn crop (Hill 2022). By 2016, it increased the price of corn by 30%, and had the knock-on effect of increasing wheat and soybean prices by 20% as acreage devoted to these crops was converted to corn. The RFS reshaped markets for field crops and drove major changes in agricultural land use.

And changed land use is mostly responsible for increasing greenhouse gas emissions from growing more corn. The crop expanded onto land less suited for it (“marginal, stepper-sloped areas”), took over areas covered with native grasses and other perennial vegetation, reduced enrollments in the land Conservation Reserve Program, and increased corn monocropping, which depletes soil while requiring more fertilizer and pesticides. All in all, these changes increased nitrous oxide (N2O) emissions from greater use of nitrogen fertilizer. Often ignored, N2O is 300 times more potent than CO2. Another major source of emissions was due to the release of carbon stored in soil as a result of clearing land (pasture, perennial grasslands, etc.) for corn production. Finally, the intensification and expansion of corn production has also increased nitrate leaching, phosphorous runoff, and soil erosion, all of which increase groundwater pollution. In turn these effluents increased emissions from downstream rivers and lakes.

Past regulatory impact analyses for the EPA used models developed by the Argonne National Laboratory and others to estimate ethanol’s carbon emissions. Using best estimates, since data was unavailable, modelers seriously underestimated impacts from changing land use (Lark 2021; Giles 2022). Hence, when Tyler et al. reran these models with subsequently collected field-level data, they found the 2022 emissions for ethanol to be at least 24% above gasoline. That is a conservative number because it does not include the emissions from increased manufacture of fossil-fuel-derived fertilizers, nor emissions from water polluted by farm-field runoff.

Recently, oil-powered transportation surpassed electricity generation as America’s top emitter of carbon dioxide. As rising emissions literally set the word ablaze, corn ethanol is adding fuel to the fire.

References

• Fenske, Jason. 2022 (Mar 4). America Was Wrong About Ethanol – Study Shows. Engineering Explained; https://youtu.be/F-yDKeya4SU
• Giles, Cynthia. 2022 (Oct). Don’t double down on past mistakes with low carbon fuels. Ch. 8 in Next Generation Compliance. Oxford; https://doi.org/10.1093/oso/9780197656747.003.0009
• Hill, Jason. 2022 (Mar 9). The Sobering truth about corn ethanol. Proceedings of the National Academy of Sciences; https://www.pnas.org/doi/epdf/10.1073/pnas.2200997119
• Lark, Tyler J. et al. 2021 (Dec 2). Environmental outcomes of the US Renewable Fuel Standard. Proceedings of the National Academy of Sciences; https://www.pnas.org/doi/abs/10.1073/pnas.2101084119
• Voelcker, John. 2014 (May 19). Driving Entirely On Ethanol: Brazil’s Volkswagen Gol Flex-Fuel Vehicle. Green Car Reports; https://www.greencarreports.com/news/1092180_driving-entirely-on-ethanol-brazils-volkswagen-gol-flex-fuel-vehicle