Corn ethanol has a positive greenhouse gas effect, says author of original GREET model; details 7 modeling errors by Searchinger team

In Washington, researchers Michael Wang, at the Argonne National Laboratory, and Zia Haq, at the Department of Energy, offered a detailed response to the Science magazine article authored by a team led by Timothy Searchinger.

Wang’s analysis shows a reduction in greenhouse gas emissions from corn ethanol, compared to the Science magazine results. In the response, the authors indicate that Searchinger’s team made errors in updating the 1999 GREET model developed at Argonne by a team led by Wang.

According to Wang and Haq, Searchinger modeled a case where corn ethanol production reached 30 billion gallons, compared to the 15 billion cap envisioned in the Energy Security and Independence Act; did not increase corn yields; underestimated the protein content of distiller’s grains by 23 percent, incorrectly assumed a 62 percent in corn exports for 2007, omitted a 400 percent increase in distiller’s grain exports, assumed constant deforestation rates in the Amazon and other areas despite downward trends, and did not account for an increase in corn ethanol production efficiency.

Wang and Haq warned policymakers that indirect land-use modeling was in its infancy and not to be misguided by accepting results as definitive at this stage of model evolution.

In a further clarification on the Science magazine controversy, an author of one of the two articles published recently in Science magazine, David Tilman, gave an interview to the Minnesota Daily regarding the study. “The goal of our paper was to point out if we do certain things, that those things would give us fuels that didn’t have very much environmental benefit,” he said. Tilman added that the paper didn’t say the problems were occurring in the present, but that they could occur in the future.

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