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Ethanol made from switch grass, a plant touted as a more sustainable feedstock for renewable fuel than corn, doesn’t qualify to be in the category of lowest-carbon biofuels under U.S. EPA’s standards for the national biofuel mandate, according to a study commissioned by one of the program’s harshest critics.
The report, prepared by University of California, Davis, Institute of Transportation Studies research scientist Richard Plevin and analyzed by the Environmental Working Group, concludes that the federal renewable fuel standard’s method for assessing the carbon intensity of switch grass biofuel differs from the calculations based on the Global Change Assessment Model, a model developed by the Pacific Northwest National Laboratory.
According to Plevin’s analysis, forests, grasslands and pastures lose their carbon sequestration potential when converted to grow switch grass. Though switch grass itself stores carbon and prevents the gas from contributing to global warming, those benefits “are dominated by the reduced sequestration by the forestry and pasture sectors,” according to Plevin’s paper. As a result, switch grass ethanol reduces emissions by 47 percent, missing the EPA threshold of 60 percent reduction to qualify as an advanced biofuel.
“I think it’s important to take a hard look to see if the RFS is going to reduce emissions or not,” said Emily Cassidy, a biofuels research analyst with EWG.
Nevertheless, the EWG analysis frames switch grass biofuel as a better alternative for cutting carbon emissions than corn ethanol, which it says has a life-cycle carbon intensity that is greater than that of gasoline, citing a 2010 study.
In an email, Plevin warned not to rely on one biofuel model.
“GCAM is just one of many models that have been applied to the question of biofuel carbon intensity. None of the models has any special status, other than perhaps having been selected by some regulator or another,” he wrote in an email. “The GCAM results also reflect how we chose to set up the model to compare a policy to a baseline. These results are just one more data point, and none of the results (ours or others) should be taken as conclusive.”
EPA’s inspector general announced last month that it would investigate whether the agency complied with its rules when assessing the climate impacts of its biofuels.
In order to qualify as an “advanced” biofuel under the RFS, a fuel must reduce greenhouse gas emissions by at least 60 percent compared with gasoline. EPA is set to finalize its proposal by Nov. 30.
Advanced Biofuels Business Council Executive Director Brooke Coleman disagreed with the conclusions of the report.
“The report is lacking in substantive information in how it reached the same information that everyone else has arrived [at],” said Coleman, adding that switch grass ethanol’s life-cycle carbon reduction score is between 60 percent and more than 100 percent compared to gasoline.
Coleman noted that Plevin’s institute at UC Davis includes board members from the oil industry, foes of the RFS. The board also includes representatives from the electric vehicle sector, automotive groups and public transportation experts.