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Building the Evidence on Corn Ethanol’s Greenhouse Gas Profile

Posted by Jan Lewandrowski, USDA Office of the Chief Economist in Energy
Jul 29, 2021
A collage of corn, scientists and a man holding a jar of ethanol
A new study looks at the greenhouse gas benefits of corn ethanol. Images courtesy of USDA.

Over the past two decades, the demand for renewable fuels — including corn-based ethanol — has helped drive a strong domestic market for corn, and supported rural America by generating jobs (PDF, 1.5 MB). New research is confirming that corn ethanol also has more greenhouse gas benefits than previously thought.

A study we just published in the journal Biofuels found that the greenhouse gas (GHG) emissions from corn ethanol are about 39 percent lower than gasoline on energy equivalent basis. The study, titled “The greenhouse gas benefits of corn ethanol—assessing recent evidence,” also found that when ethanol is produced at natural gas-powered refineries, the GHG emissions are even lower—around 43 percent below gasoline. This study confirms work that we released in 2018 (PDF, 3 MB) and adds to the mounting evidence of ethanol’s GHG benefits, which have been often overlooked.

Unlike estimates of ethanol’s GHG profile from the early 2000’s, which relied on projections of how growing corn for fuel would impact emissions, we now have the benefit of looking back in time to see how the industry responded to the requirements of the Renewable Fuels Standard (RFS). As it turns out, the data show that the last decade was a time of great innovation and productivity improvement in both corn production and ethanol refinery technologies. The story of how farmers and ethanol producers responded to the requirements of the RFS is one worth understanding—and this story is now being told in the peer-reviewed literature.

Projections of Increased GHG Emissions due to Land-Use Change Didn’t Materialize

Earlier estimates of ethanol’s GHG emissions assumed the increased price of corn (caused by increased demand for corn ethanol) would result in farmers bringing new land into production (otherwise known as land-use change). Projections warned of an increase in GHG emissions from tilling native grassland, and converting wetlands and forests for corn production. More recent research shows that, while there has been some conversion and reallocation of land, things did not end up playing out the way these earlier projections anticipated.

A 2015 study published in the Annual Review of Resource Economics showed that although higher corn prices gave an incentive to farmers to grow more corn, farmers responded with increases in double-cropping and planting in fields that were fallow, and reducing temporary pasture to increase corn production—and far less land use change than originally predicted. In other words, although farmers produced more corn, they relied on improved technology and intensive cropping on existing fields rather than converting new lands into production.

Another study published last year in the American Journal of Agricultural Economics found that between 2003 and 2014, increases in ethanol demand alone led to a 3 percent increase in corn acreage, and less than one percent increase in total crop acreage in the United States by 2012 compared to 2008. This was a far smaller impact than previously projected.

These studies demonstrate that although there were additional acres brought into corn production as a result of ethanol demand, the land use change impacts weren’t nearly as drastic as we once thought.

Better Refining Technology and Land Management Have Also Improved Ethanol’s GHG Balance

But it isn’t just land use change that influences the GHG balance of ethanol. How corn is produced on farms and how refineries operate can also have a large impact on greenhouse gases, from the changes in soil carbon and the emissions associated with growing crops, to the GHG emissions from producing the fuel.

Independent of our study, another recent analysis titled, “Land management change greatly impacts biofuels’ greenhouse gas emissions,” and published in the journal Global Change Biology Bioenergy in 2018 found that when corn farmers adopt practices that increase soil organic carbon, such as using manure and cover crops, the lifecycle GHG emissions for ethanol are about 40 percent lower than gasoline.

Our article in the journal Biofuels also assessed the GHG impacts of improved technologies. These include adopting conservation (PDF, 7.6 MB) on corn farms, such as cover crops, no-till, and precision agriculture technology, which can decrease emissions on the farm level. Combined with efficiency improvements in refineries, such as switching to biomass as a process fuel, these improvements could result in a 70 percent lower GHG emission profile for ethanol over gasoline by 2022.

Refinery efficiency improvements can have benefits beyond reducing GHG emissions as well, such as producing co-products like corn oil. Since 2010, ethanol refineries have evolved by adopting more efficient processes to produce more ethanol per bushel of corn. Of course, taking these changes into account further drives down ethanol’s lifecycle GHG emissions.

All this research aside, there are certainly environmental tradeoffs involved in ethanol production. Any form of energy production has social and environmental costs. However, when it comes to GHGs, the evidence demonstrates that corn ethanol is a net positive compared with gasoline—and there is room for continued improvement.

There’s one more point worth mentioning here: incentivizing ethanol through the Renewable Fuels Standard has offset 10 percent of our reliance on fossil fuels in the transportation sector. No matter how you look at it, that’s progress towards a cleaner energy future.

Category/Topic: Energy

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Marc J. Rauch
Apr 05, 2019

This is a very welcome authoritative study that 'once again' states that the production and use of corn ethanol is a cleaner, safer, and economically viable alternative to the poison fuels that come from petroleum oil.

I say 'once again,' because this isn't the first study to reach this conclusion - there have been a few others over the years (listed below). Unfortunately, in their never ending greedy mission to force more of their poison down our throats, the oil industry keeps trying new ways to present their same old lies against ethanol and therefore keeps having their shills pretend like they've found new evidence against ethanol.

It would be great if the oil industry stopped the nonsense on their own, but they probably won't so we should expect more deaths, illnesses, and wars caused by their actions.

On the bright side, America's farming and ethanol communities have heroically risen to a great challenge and defeated all the naysayers. They will continue to innovate, increase crop yields and ethanol output, and add in other crops and materials to further expand ethanol output as consumer demand increases (and as higher ethanol-gasoline blends are made available at the pump).

Innovation is Driving Down Greenhouse Gas Emissions from Corn-based Ethanol…

Argonne Lowers Land Use Change GHG Emissions For Corn Ethanol…

Review and Evaluation of Studies on the Use of E15 in Light-Duty Vehicles…

Land-use change and greenhouse gas emissions from corn and cellulosic ethanol…

Fuel Ethanol Produced from Midwest U.S. Corn: Help or Hindrance to the Vision of Kyoto?

andrew mcneil
Apr 24, 2019

If ethanol was really economically viable you wouldn't need to pass laws to make people buy it. Oil companies, being greedy, would replace gas with ethanol and pocket the difference.

Guy J Swanson
Apr 28, 2020

Yes on this report to a cleaner energy future and furthermore the technology of GHG emission reduction continues to improve with Exactrix application of TAPPKTS and TAPPS with Micros.

The technology exists to reduce N2O emissions to zero with fertilizer application technology developed in Exactrix Laboratories. These systems are now on test across the Great Plains and the PNW.

It will not be long before CO2, CH4 and N2O reduction technologies are available to corn producers at much lower emission levels. Exactrix anticipates up to 3 to 10 times greater advantage over other approaches for producing and highly efficient corn.

Rakesh Mehrotra
Sep 11, 2021

Corn ethanol LCA in US (Far more per capita land and other resources) and sugar cane based ethanol are not comparable.

Alexander Cokonis
Feb 16, 2022

The test for biofuels should be to see if the energy required to produce it is less than the output energy. That will determine whether it is a good candidate for replacing fossil fuels when they run out in the future.

Mary Shapiro
Apr 12, 2022

I don't know why we stopped pushing for flex fuel cars . Brazil has almost 100% ethanol cars. They have been using it for over 20 years. Does the oil industry have deep pockets ? We only would have to change a small converter in any automobile to use ethanol.Doesn't producing electric for charging batteries produce green house gases and the price of electric cars is very high. Not to mention that the batteries used in electric cars are at times dangerous they have the ability to explode.

Tibor Nemeth
Apr 19, 2022

Could you specify the average EROI for corn-based methanol in the US? That is an important factor on the utility of the methanol usage in transportation.

Ben Weaver
Apr 19, 2022

@Tibor Nemeth - thank you for your inquiry. It was forwarded to the Office of Energy and Environmental Policy.

You used the term “methanol” in the text of your question but linked to a USDA blog post on ethanol. Methanol and ethanol are different types of alcohol with different production processes and uses. Most methanol in North America is produced from natural gas, while most ethanol in North America is produced from corn. Methanol can be used as fuel but is not widely available for this purpose. Ethanol, on the other hand, makes up about 10% of U.S. gasoline supply, and ethanol’s share of gasoline is slowly increasing.

Here is a link to our most recent work on the energy balance of corn ethanol: 2015 Energy Balance for the Corn-Ethanol Industry. This analysis found that corn ethanol plants produce 2.1 Btu of ethanol for every Btu of energy input. Given the trend toward better efficiency at corn ethanol plants, I would expect to find an even more favorable energy balance using more recent data.

Let us know if you have additional questions.

Tony Radich
Office of the Chief Economist/Office of Energy and Environmental Policy

Jim Hatheway
Jul 26, 2022

Excellent. Thank you from the home state of the Paxton Syphon.