Growing corn for ethanol may increase greenhouse gases for over a century.

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 for
  livestock feed as well as food crops. By 2016 about 43 percent of that
  area will be used to harvest corn for ethanol.
  
  
• 27 percent of new palm oil plantations in Indonesia are created on
  land that began as tropical rain forest; 1.5 percent of these lands are
  being 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 is
  expected to more than double with new plants and expansion of existing
  ones.
  
  
• 2006 ethanol capacity was 4.4 billion gallons, with an expected
  increase of 2.1 billion gallons with current construction and expansion
  projects.
  
  
• 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 Michigan
State University, says there is a huge amount of uncertainty when
basing predictions on an inherently complex economic model.
Additionally, he asserts that the United States should not be
responsible for “anything but its own environmental profile” and that
to take into account world land changes is unreasonable. Nathanael
Greene of the Natural Resources Defense Council responds that it is
appropriate to incorporate economic models into life-cycle emissions
analyses such as these. In contrast to Dale, he says that land-use
changes in other nations should not be left out of calculations of
biofuel impacts, since such indirect effects are commonly incorporated
into environmental regulations.