A new study from University of Michigan researchers challenges the widely held assumption that biofuels such as ethanol and biodiesel are inherently carbon neutral.
Contrary to popular belief, the heat-trapping carbon dioxide gas emitted when biofuels are burned is not fully balanced by the CO2 uptake that occurs as the plants grow, according to a study by research professor John DeCicco and co-authors at the U-M Energy Institute.
The study, based on U.S. Department of Agriculture crop-production data, shows that during the period when U.S. biofuel production rapidly ramped up, the increased carbon dioxide uptake by the crops was only enough to offset 37 percent of the CO2 emissions due to biofuel combustion.
The researchers conclude that rising biofuel use has been associated with a net increase—rather than a net decrease, as many have claimed—in the carbon dioxide emissions that cause global warming. The findings are scheduled to be published online Aug. 25 in the journal Climatic Change.
“This is the first study to carefully examine the carbon on farmland when biofuels are grown, instead of just making assumptions about it,” DeCicco said. “When you look at what’s actually happening on the land, you find that not enough carbon is being removed from the atmosphere to balance what’s coming out of the tailpipe.”