Study questions climate benefits of corn ethanol

Source: Amanda Peterka, E&E reporter • Posted: Thursday, August 13, 2015

University of Michigan researchers today raised questions about the greenhouse gas benefits of producing ethanol from corn.

In a study, the researchers looked at how carbon dioxide moves between land and the air and found that, in a best-case scenario, substituting ethanol for gasoline produces no significant net changes in emissions.

The authors used “annual basis carbon” accounting to examine the greenhouse gas emissions associated with growing corn for producing and using ethanol. They say the method is more accurate for measuring the carbon footprint of biofuels than the life-cycle assessments used in regulatory decisions.

“Biofuels have been getting a bad rap recently and so one might ask, ‘Isn’t this just yet another study criticizing corn ethanol?'” University of Michigan energy researcher and study author John DeCicco wrote in a blog post today. “What is distinctive here is the use of a scientifically rigorous method termed annual basis carbon (ABC) accounting rather than the lifecycle assessment (LCA) methods that are commonly used.”

Ethanol advocates called the work a “sham study” and said it ignored the full life-cycle carbon impact of the fossil fuels sector.

The study was funded by the American Petroleum Institute and the University of Michigan Energy Institute. The authors said the study was not meant to be taken as representing the views of either API — a vocal critic of U.S. biofuel policies — or the university initiative, which is focused on transportation-related energy issues.

DeCicco has previously raised doubts about the ability of today’s life-cycle analyses to capture the full greenhouse gas impacts of ethanol production (Greenwire, Sept. 26, 2013). Earlier this week, DeCicco penned an editorial in The Hill, calling on Congress to repeal the renewable fuel standard, which requires refiners to blend ethanol and advanced biofuels in petroleum gasoline and diesel.

In today’s study, he and co-author Rashmi Krishnan argue that LCA doesn’t fully account for carbon dioxide that is removed from the atmosphere by corn plants before they are converted to ethanol.

The authors said annual basis carbon accounting, which takes into account both carbon dioxide uptake and emissions, is more useful for measuring the greenhouse gas impacts of ethanol. They argue that the method shows that reductions in the uptake of carbon dioxide when plants are harvested for ethanol production are not enough to balance out unchanged tailpipe emissions when ethanol is burned in cars.

“Although it may account for all of the CO2 being discharged into the air, where LCA goes wrong is in not counting all of the ‘negative emissions,’ that is, CO2 being removed from the atmosphere through plant growth,” DeCicco wrote in the blog post. “Correcting this mistake by carefully accounting for CO2 uptake greatly changes the picture.”

Using the annual basis carbon method and data obtained from a corn ethanol facility in Illinois, the authors examined different corn yield scenarios. Under the worst case, net greenhouse gas emissions were 70 percent higher when using corn ethanol than when using petroleum gasoline.

“The implication is that, in the real-world of commercial feedstock production, biofuels are clearly not carbon neutral,” the authors said in the study.

Ethanol advocates have disputed prior studies that have questioned the corn-based fuel’s greenhouse gas benefits.

“Professor DeCicco has been making these arguments for years, and for years they have been rejected by the scientific community and life-cycle analysis experts,” said Geoff Cooper, senior vice president at the Renewable Fuels Association. “The only thing new and different about this paper is the fact that the American Petroleum Institute is explicitly recognized as the sponsor of the work, disclosing once and for all who is really behind the effort to obscure and confuse accepted bioenergy carbon accounting practices.”

The University of Michigan study authors note that plugging in the same data from the Illinois facility into Argonne National Laboratory’s GREET model, a popular life-cycle assessment tool, showed that corn ethanol reduced greenhouse gas emissions by 40 percent compared with gasoline.