The practice can release large amounts of stored carbon
By Deane Morrison
University Regents Professor of Ecology David Tilman (right) and Joe Fargione of the Nature Conservancy urge that all stages of biofuel production, distribution, and use be evaluated for their environmental impacts.
February 7, 2008
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 today in Science. The researchers document how the act of turning rainforests, peatlands, savannas, or grasslands into 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, land is being 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 go on for 50 years or longer.
The atmosphere contains a lot of carbon, but about 2.7 times more is stored in terrestrial soils and plant material. Converting virgin land for crops releases carbon dioxide quickly during the early stages, but releases may continue for decades as coarse roots and branches and wood products decay or burn.
Indonesia and Malaysia account for 86 percent of global palm oil production. Demand for palm oil, which is used for food or to make biodiesel, contributes to the 1.5 percent annual rate of deforestation of tropical rainforests in these nations. An estimated 27 percent of concessions for new palm oil plantations are on peatland tropical rainforests, whose destruction releases the most carbon dioxide of the ecosystems in this study.
"The research examines the conversion of land for biofuels and asks the question, 'Is it worth it?'. Surprisingly, the answer is no."Increased demand for ethanol corn crops is likely contributing to conversion of the Brazilian Amazon and tropical savanna, the researchers say. American farmers traditionally rotated corn with soybeans, but now they are planting corn every year to meet the ethanol demand, and Brazilian farmers are deforesting the Amazon to plant more soybeans.
Stephen Polasky, a professor of applied economics, studies environmental and resource economics, among other topics.
"We analyzed all the benefits of using biofuels as alternatives to oil, but we found that the benefits fall far short of the carbon losses," says Fargione. "If you're trying to mitigate global warming, it simply does not make sense to convert land for biofuels production. "All the biofuels we use now cause habitat destruction, either directly or indirectly. Global agriculture is already producing food for six billion people. Producing food-based biofuel, too, will require that still more land be converted to agriculture." Also, high energy prices will turn up the pressure for biofuel production, says Polasky, and this could lead to large-scale land conversion.
© 2009-2011 Regents of the University of Minnesota. All rights reserved.
The University of Minnesota is an equal opportunity educator and employer
Last modified on March 9, 2009