The greenhouse gas benefits of corn ethanol – assessing recent evidence

Abstract

In 2010, the U.S. Environmental Protection Agency (EPA) released a life-cycle analysis of the greenhouse gas (GHG) emissions associated with the production and combustion of corn ethanol. EPA projected that by 2022, the emissions profile of corn ethanol from a new refinery would be 21% lower than that of an energy equivalent quantity of gasoline. Since 2010, the 21% value has dominated policy discussions and federal regulations related to corn ethanol as a renewable fuel and a GHG mitigation option. It is now 2018 and new data, scientific studies, technical reports, and other information allow us to examine the emissions pathway corn-ethanol has actually followed since 2010. Using this information, we assess corn ethanol's current GHG profile at 39-43% lower than gasoline. We also develop two projected emissions scenarios for corn ethanol in 2022. These scenarios highlight opportunities to produce ethanol with emissions that are 47.0-70.0% lower than gasoline. Many countries are now developing or revising renewable energy policies. Typically, biofuel substitutes for gasoline are required to reduce GHG emissions by more than 21%. Our results could help position U.S. corn ethanol to compete in these new and growing markets.

Retrospective analysis of the U.S. corn ethanol industry for 2005–2019: implications for greenhouse gas emission reductions

“…The 2021 report 11 calculated the CI of corn ethanol to be 53.2 gCO 2 e/MJ (including LUC GHG emissions of 7.4 gCO 2 e/MJ) in 2020. The US Department of Agriculture (USDA) published several reports on the CI of US corn ethanol using the GREET model 4,12–14 . These reports, with a LUC GHG value of 6.7 gCO 2 e/MJ, show a CI of 52.8–56.6 gCO 2 e/MJ for corn ethanol between 2014 and 2019, and project a CI of 47.9–51.7 gCO 2 e/MJ for 2022.…”

“…There have been continuous requests to update LCA results with primary data for corn ethanol that reflect the improvements in this industry 13 . The objective of this study is to evaluate the historic trends in corn ethanol CI over the 15 years from 2005 to 2019, using primary data for US corn farming and ethanol production with survey data collected by USDA and the ethanol industry.…”

Techno-economic analysis of long-duration energy storage and flexible power generation technologies to support high-variable renewable energy grids

“…They are, however, significantly less constrained by location, although ethanol could be constrained by competition with food production for resources such as land, water, and fertilizer. Ethanol also requires substantial reductions in life-cycle emissions to approach ''carbon-neutral'' status, [68][69][70] and lower emission biofuel production pathways, such as cellulosic biomass, require further development to reach production cost targets. 71 This study is limited by the assumptions around the construction, dispatch, and operation of seasonal energy storage and flexible power generation technologies.…”

Life cycle greenhouse gas emissions of ethanol produced via fermentation of sugars derived from shrub willow (Salix ssp.) hot water extraction in the Northeast United States

“…Bioethanol from corn is cost effective and its infrastructure for production, blending with gasoline, and distribution have been deployed nationwide over the last two decades. However, the potential GHG savings from corn ethanol is only in the range of 39–43%, which is still far from being a net zero or net negative GHG emissions transportation fuel [ 4 ]. Lignocellulosic ethanol can reach and exceed the 60% GHG reduction mandated by the Renewable Fuel Standard (RFS) program to become a net negative GHG emissions fuel.…”