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Converting pristine lands to biofuel farms worsens global warming


The practice can release large amounts of stored carbon

By Deane Morrison

David Tilman, Joe Fargione
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.

Grim reaping

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 land conversions pump out 17 to 423 times more carbon than the annual savings from replacing fossil fuels with the biofuels. This constitutes a "carbon debt" that the biofuels produced on the land must pay off before they can begin to have the effect of cutting greenhouse gas emissions. In the worst case the researchers examined, converting peatlands 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 , 'Is it worth it?,'" says lead author Joe Fargione, a scientist for the Nature Conservancy. "Surprisingly, the answer is no." Fargione began the work when he was a University postdoctoral researcher with Stephen Polasky, an applied economics professor, and David Tilman, a Regents Professor of Ecology; both are co-authors of the paper. Economic forces have a lot to do with how biofuels are produced. "Landowners are rewarded for producing palm oil and other products but not rewarded for carbon management," says Polasky. "This [encourages] excessive land clearing and can result in large increases in carbon emissions."

"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
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.

Perennial solution

To reverse this trend, the researchers want to see biofuels produced from waste plant material such as corn stover or from native grasses and woody plants grown on marginal lands unsuitable for crops. "Biofuels made on perennial crops grown on degraded land that is no longer useful for growing food crops may actually help us fight global warming," says U researcher and co-author Jason Hill. "One example is ethanol made from diverse mixtures of native prairie plants. Minnesota is well poised in this respect." Tilman, who led a study that found meager ecological benefits from corn ethanol, says this kind of biofuel production would minimize habitat destruction, competition with food production, and carbon debts. "In the United States, Conservation Reserve Program [CRP] lands, idle lands, and others that had once been in agriculture can be used to grow appropriate biofuels, and in so doing give us energy sources that are much better than gasoline and other fossil fuels," he says. "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." As for stopping the destruction of pristine lands abroad, the researchers say laws, as well as treaties dealing with biofuel imports, must stipulate responsible practices for growing, producing and distributing biofuels and cite the U.S. Energy Independence and Security Act of 2007 as a step in the right direction. They also advocate that negotiators seeking to extend the Kyoto Protocol beyond 2012 address the problem of emissions from land use changes due to higher demand for biofuels. "We will need to implement many approaches simultaneously to solve climate change," says Fargione. "There is no silver bullet, but there are many silver BBs. Some biofuels may be silver BBs, but only if produced without requiring additional land to be converted from native habitats to agriculture." University researcher Peter Hawthorne also contributed to the work.