Turning pristine land into biofuel farms could make global warming worse
Switching from fossil fuels to renewable biofuels is supposed to mitigate global warming, not make it worse.
Yet that’s what happens when native ecosystems are converted into “farms” for biofuel crops, according to a study by the University of Minnesota and the Nature Conservancy published online in Science on February 7. The researchers document how clearing rainforests, peatlands, savannas or grasslands to make way for biofuel-yielding croplands emits large amounts of carbon that add to the atmosphere’s already heavy burden of greenhouse gases.
The work shows that biofuels produced this way can cause more emissions than gasoline.
In places like Brazil, Southeast Asia and the United States, pristine land is being cleared and planted with corn or sugarcane to produce ethanol, or with palm trees or soybeans to produce biodiesel. The carbon, stored in the original plants and soil, is released as carbon dioxide when that organic matter decays, which can take 50 years or longer.
The land conversions pump out 17 to 423 times more carbon than the annual savings from replacing fossil fuels with biofuels. This constitutes a “carbon debt” that the biofuels produced on the land must pay off before they can begin to cut greenhouse gas emissions.
In the worst case the researchers examined, converting peatland rainforests in Indonesia into palm oil plantations ran up a carbon debt that would take 423 years to pay off. The next worst was soybeans in the Amazon, which wouldn’t “pay for themselves” in renewable soy biodiesel for 319 years. The conversion of U.S. grasslands for corn ethanol and Indonesian rainforests for palm biodiesel also ran up big carbon debts.
“The research examines the conversion of land for biofuels and asks the question, ‘Is it worth it?,’” says lead author Joe Fargione, a scientist for the Nature Conservancy. “Surprisingly, the answer is no.” Fargione began the work as a University postdoctoral researcher with Stephen Polasky, applied economics professor, and David Tilman, Regents Professor of Ecology; both are co-authors of the paper.
A better alternative, the researchers say, is making biofuels from waste plant material such as corn stover or from native grasses and woody plants grown on marginal lands unsuitable for crops.
“Biofuels made from perennial crops grown on degraded land that is no longer useful for growing food crops may actually help us fight global warming,” says co-author Jason Hill, a research associate in the Department of Applied Economics. “One example is ethanol made from diverse mixtures of native prairie plants. Minnesota is well poised in this respect.”
Tilman adds that “biofuels made from waste biomass or from biomass grown on abandoned agricultural lands planted with perennials incur little or no carbon debt and offer immediate and sustained greenhouse gas advantages.”
Co-author Peter Hawthorne located numbers used in the calculations, conducted a statistical analysis, and linked the research to global and regional patterns of land use and availability. —Deane Morrison
