Governors' Biofuels Coalition

A study linking U.S. biofuel policies to the loss of grasslands lacked statistical proof to back up its conclusions, according to the Energy Department’s Argonne National Laboratory.

At issue is a study published last month by Environmental Research Letters that tracked land-use changes between 2008 and 2012 — a period of high crop commodity prices and the onset of the federal renewable fuel standard. Of the more than 7 million acres plowed for crops, 5.7 million acres were grasslands, important landscapes for wildlife habitat and carbon sequestration (E&ENews PM, April 2).

The findings are not necessarily incorrect, the Argonne review says. The analysis, reviewers said, was “careful and thorough.”

But the paper’s authors — Tyler Lark, Meghan Salmon and Holly Gibbs of the University of Wisconsin, Madison — failed to test their data from the Cropland Data Layer and the National Land Cover Database against an error analysis. Doing so may have affected their results, especially in states with a reported high rate of crop conversion. These include North Dakota and South Dakota but also some of the lowest accuracy levels for the data.

To verify study results, Argonne scientists used the Agriculture Department’s National Agriculture Imagery Program (NAIP), which produces high-resolution imagery of agricultural lands on an annual basis. The “hot spots” in the Dakotas, as found by Lark and Gibbs, were not apparent.

“There is no indication that this type of transition has occurred on a large scale in the identified ‘hot spot’ regions. However, land use in these areas is complex and more thorough follow-up analyses are indeed needed,” Argonne scientists wrote.

Furthermore, the authors should have taken into account geographical differences in soil carbon sequestration rates — which can change from state to state — when making conclusions on soil carbon loss, the Argonne scientists said. Given that much of the agricultural land would be used to produce biofuels, the reduction in greenhouse gases from transportation could offset potential losses from soil sequestration.

“While land use is a critical issue, so too is the reduction of [greenhouse gas] emissions from the transportation sector, and biofuels are one key route to this aim,” they wrote.

The ethanol trade group the Renewable Fuels Association criticized the study shortly after its publication, calling the data used “error-prone.”

Lark, the study’s lead author, agreed with many of the points in the review. He said the study was undertaken to provide for a “back-of-the-envelope first estimate” of cropland conversion and that the reviewers’ suggestions were a welcomed extension to the study.

Lark added that he took multiple steps to improve the accuracy within the data sets, combining them in a way that would avoid magnifying any potential errors. The article, he said, was not intended to lay the blame on any one policy, like the RFS.

“We didn’t assign conversion to any specific policy,” he said, but were “reconciling the differences with what those policies set out to achieve.”

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