If the climate continues to evolve as predicted by the Intergovernmental Panel on Climate Change, the United States stands little to no chance of satisfying its current biofuel goals, according to a new study by Rice University and the University of California at Davis.

The study published online in the American Chemical Society journal Environmental Science and Technology suggests that in 40 years, a hotter planet would cut the yield of corn grown for ethanol in the U.S. by an average of 7 percent while increasing the amount of irrigation necessary by 9 percent. 

That could sharply hinder a mandate set by the Energy Independence and Security Act of 2007 (EISA) that by 2022 the nation derive 15 billion gallons per year of ethanol from corn to blend with conventional motor fuels, according to principal investigator Pedro Alvarez, the George R. Brown Professor and chair of Rice's Civil and Environmental Engineering Department. Alvarez is a member of the Science Advisory Board of the U.S. Environmental Protection Agency and chair of Rice’s Energy and Environment Initiative.

The policy is based on the idea that blending ethanol into gasoline cuts harmful emissions from vehicles and lowers the nation’s dependence on foreign oil, he said. But the cost in water may outweigh those concerns. 

“Whereas biofuels offer a means to use more renewable energy while decreasing reliance on imported oil, it is important to recognize the tradeoffs,” Alvarez said. “One important unintended consequence may be the aggravation of water scarcity by increased irrigation in some regions.”

 

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The authors of the new paper have long questioned the United States’ support of biofuels as a means to cut vehicle emissions. In a 2010 white paper on U.S. biofuels policy produced by Rice’s Baker Institute for Public Policy, authors including Alvarez and Rice alumna Rosa Dominguez-Faus found “no scientific consensus on the climate-friendly nature of U.S.-produced corn-based ethanol” and detailed what they saw as economic, environmental and logistical shortcomings in the EISA. 

Their 2009 feature article in Environmental Science and Technology suggested the amount of water required to bring biofuels to market may be prohibitive; they calculated it takes 50 gallons of water to grow enough Nebraska corn to produce the amount of ethanol needed to drive one mile.

They suggested at the time that potential consequences to the water supply needed further study. With the new research, they have taken on that challenge and tied their models to estimates of how climate change -- reflected in predicted regional levels of atmospheric carbon dioxide, temperature and precipitation -- could affect agriculture in the nation’s heartlands.