THE STUDIES “Land Clearing and the Carbon Biofuel Debt” by Joseph Fargione et al., and “Use of U.S. Croplands for Biofuels Increases Greenhouse Gases Through Emissions From Land Use Change” by Timothy Searchinger et al., both published in the February 7, 2008, issue of Science.

THE QUESTION Will switching from fossil fuels to biofuels really reduce greenhouse gases? We take a close look at two big, controversial studies that examine carbon emissions from the ecosystems torn down to produce biofuels.

THE METHODS Throughout the Amazonian rain forest and the savanna of Brazil, enormous swaths of land are being converted to farms for growing soybeans and sugarcane—all for use in creating biofuels. The tropical rain forest and peatland of Indonesia and Malaysia and the grasslands of the United States are also being converted to biofuel crops. It is a disturbing trend, says Joseph Fargione, regional science director at the Nature Conservancy, who conducted the first of the two studies examined here. With his colleagues Fargione took a close look at how the areas being transformed into farmland have acted as carbon dioxide storage systems. Trees, grass, and other flora take in the gas, Fargione says, incorporating the carbon into their structures. But when the land is converted for agriculture, the plants are cut down, burned, or processed, and the stored carbon is eventually released back into the atmosphere as greenhouse gases. Using numbers from nearly 50 previous studies, Fargione’s team calculated the amount of carbon stored in these landscapes and the up-front carbon cost for each acre of land converted to produce biofuels.

In the second study, Timothy Searchinger, a researcher at Princeton University, looked at a future scenario in which the United States substantially increases its production of corn-based ethanol, a move that would decrease domestic crops for food and feedstock. These feed crops have to be grown somewhere, however, and the worldwide land conversions necessary to make up for lost U.S. crops would release carbon dioxide. To show the effect of such changes, Searchinger and his colleagues simulated the worldwide land-use changes necessary to offset the production of 56 billion liters of ethanol in the United States (the amount of ethanol projected to be processed in 2016, based on current tax credits and conservative estimates of oil prices). Using an economic model created at Iowa State University, the researchers projected how much land farmers around the world would have to convert to feed-crop production, and where they would do it. From this the researchers were able to estimate the total greenhouse emissions due to land conversion.

THE RESULTS Both studies found that changes in land use related to biofuel production would be a significant source of greenhouse gases in the future. Fargione reported that, overall, biofuels would cause higher total emissions for tens to hundreds of years. Some ecosystems had surprisingly high emissions—grasslands in the United States converted to corn farms would increase carbon dioxide for 93 years.

Searchinger’s outlook is bleaker: He estimates that the rise in corn-based ethanol production in the United States would increase greenhouse gases, relative to what our current, fossil-fuel-based economy produces, for 167 years.

THE MEANING “Any biofuel that causes clearing of natural ecosystems is likely to increase global warming,” Fargione says. But not all bio­fuels are alike. For one, sugarcane ethanol, produced in Brazil, stands out to both researchers as the most efficient source studied, in terms of emissions. As long as there is land conversion, though, biofuels do not diminish carbon dioxide emissions. Biofuels made from sources that do not require land conversion, such as corn stover (the parts of corn plants left over after the ears are harvested), animal waste, damaged trees, algae, and food waste are promising alternatives.

STATS BEHIND THE STUDY • Plants and soils contain almost three times as much carbon as the atmosphere. • About 20 percent of total current carbon emissions comes from land-use change. • In 2004, 74 million acres of U.S. land were devoted to corn forlivestock feed as well as food crops. By 2016 about 43 percent of thatarea will be used to harvest corn for ethanol. • 27 percent of new palm oil plantations in Indonesia are created onland that began as tropical rain forest; 1.5 percent of these lands arebeing deforested each year. • In 2006 the United States produced 250 million gallons of biodiesel.Total production capacity is already 1.4 billion gallons a year and isexpected to more than double with new plants and expansion of existingones. • 2006 ethanol capacity was 4.4 billion gallons, with an expectedincrease of 2.1 billion gallons with current construction and expansionprojects. • U.S. gasoline consumption is 389 million gallons per day, or about 142 billion gallons per year.

ANOTHER VIEW Bruce Dale, a biofuels researcher at MichiganState University, says there is a huge amount of uncertainty whenbasing predictions on an inherently complex economic model.Additionally, he asserts that the United States should not beresponsible for “anything but its own environmental profile” and thatto take into account world land changes is unreasonable. NathanaelGreene of the Natural Resources Defense Council responds that it isappropriate to incorporate economic models into life-cycle emissionsanalyses such as these. In contrast to Dale, he says that land-usechanges in other nations should not be left out of calculations ofbiofuel impacts, since such indirect effects are commonly incorporatedinto environmental regulations.

POTENTIAL ALTERNATIVES Using agricultural waste rather than actual agriculture to create biofuels removes the need for land conversion—much of the stuff is just lying around—and produces more fuel than corn:

In thecase of corn stover (the leaves andstalks remaining in the field after corn is harvested), 250 million dry tonsare produced each year and are rarely utilized, other than to feed grazingcattle immediately after a harvest. Scientists believe that some stover shouldremain in the field to prevent soil erosion, but that still leaves about 40 to 50percent to be used in making biofuels. An efficient way to break down celluloseinto ethanol is necessary to reduce the cost of processing corn stover on acommercial scale. Last February, the Department of Energy selected sixcompanies to receive funding towards building ethanol plants—scheduled to beoperational within the next three years—that will utilize new technology forprocessing corn stover as well as other types of agricultural waste.

Incontrast to corn stover, wood wastehas limited potential due to the high cost associated with collection andtransportation (in the case of wood left over from timber harvesting) andcompeting uses (in the case of mill residues, which are currently used formulch, particle board, and to power other facilities).

Many farmshave already developed methods of converting the billions of tons of animal waste produced each year intomethane for electrical and heat energy; beginning in March, 1,200 households inCalifornia will be powered by cow manure. Still, using animal waste to createbiofuels is not yet feasible on the national level because transporting it isunrealistic. It's in areas where there are lots of cattle (and the large amountsof manure they inevitably give back to the world) that companies are bestequipped to divert animal waste from contaminating the air (via methane, CO 2 ,and ammonia gases) and water towards fueling ethanol production. One example isPanda Ethanol, which is building the largest biomass plant in the United Statesin Hereford, Texas, where it will use the waste of 3.5 milliongrazing cattle to fuel the production of approximately 115 million gallons ofethanol per year.

In theUnited States, 96 billion pounds of foodis wasted each year and much of it ends up in landfills where it emitsgreenhouse gases. Through anaerobic digestion—the bacterial breakdown oforganic materials—food waste can be converted into biofuel. In California,Onsite Power Systems, Inc. has begun commercial production of an anaerobicdigester system that uses a special design to create the optimal environmentfor bacteria and ultimately more efficient and cost-effective conversion offood waste to biogases (hydrogen and methane). These biogases can be used incars or to heat homes.

Algae may be the most promising biofuel.Not only does algae use carbon dioxide to grow (and could potentially use CO2from power plants to create biofuel), but it can grow anywhere and does notrequire a large area to propagate. Somespecies are made of up to 50% of their body weight in oil which can beextracted and processed to create biodiesel. Currently, the National Renewable Energy Laboratory is collaborating withChevron to develop more cost-effective processes for growing and harvestinglarge quantities of the green fuel.