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Under the Renewable Fuels Standard (RFS), signed into law as part of the Energy Independence and Security Act of 2007, the United States will be producing 36 billion gallons of renewable fuels annually in 2022, with 15 billion of that to come from corn ethanol by 2015. The ethanol conversion plant business is booming. According to the Renewable Fuels Association, a trade group, as of one year ago 114 plants in 19 states had an annual capacity of 5.6 billion gallons per year, and 80 plants—enough to double current capacity—were under construction. All three presidential candidates jumped on the ethanol bandwagon long ago, with Hillary Clinton calling for 60 billion gallons by 2030 at a campaign stop last November (all three have since back-pedaled in the face of concerns about the impact of corn ethanol on food supplies).  The motivation for all this renewable fuel is not just energy independence but also mitigation of global climate disruption, which has been called “the defining challenge of our era” by United Nations secretary-general Ban Kimoon. Among other disquieting scenarios, climate change threatens the world’s food supply. “[T]he current models of climate change impacts on agriculture are showing earlier and more rapid declines in agricultural productivity,” said John P. Holdren, director of the Woods Hole Research Center, in an interview published on the Habitable Planet website. “[T]he models of climate change influence on agriculture do not yet adequately incorporate the effects of a warmer, wetter world on crop pests and pathogens at all. . . . But every ecologist will tell you that crop pests and pathogens do better in a warmer, wetter world.”  Emissions of carbon dioxide (CO2), the chief greenhouse gas behind climate change, also threaten to acidify the oceans, decimating the plankton that form the bottom of the oceanic food chain and preventing shell formation in shellfish, according to research described by Elizabeth Kolbert in the 20 November 2006 New Yorker. Climate change also threatens to flood most of the world’s major coastal cities.  Transportation accounts for about 27% of anthropogenic emissions of CO2, according to the draft Inventory of the U.S. Greenhouse Gas Emissions and Sinks: 1990–2006, which the EPA put out for public comment on 7 March 2008. Because they are renewable, biofuels have been held up as probably the fastest and easiest fix to a large part of the carbon problem. Now, two studies published in Science on 29 February 2008 have thrown a cold wet blanket on biofuels, claiming that clearing new land and converting existing cropland to produce feedstocks incurs a “carbon debt”—that is, releases more carbon than is saved by the biofuels produced. Moreover, this debt won’t be fully repaid for tens to hundreds of years, depending on the original carbon content of the land, the type of biofuel, and the efficiency of converting the biomass to biofuels. Thus, within the critical time frame for avoiding a climate catastrophe—the next couple of decades, according to the February 2007 United Nations report Confronting Climate Change: Avoiding the Unmanageable and Managing the Unavoidable—biofuel crops will only aggravate global climate disruption.  Biofuel proponents argue that the two Science papers ignore rising agricultural productivity and the fact that the carbon impact of gasoline—the baseline for comparison—is a moving target, as rising prices encourage exploitation of tar sands and coal liquefaction, which will boost gasoline’s carbon footprint. They assert that several other important factors were also not accounted for: the value of distillers grains, a protein-rich livestock feed that is a by-product of ethanol; rising conversion plant efficiency; and carbon sequestration by alternative agricultural methods such as no-till farming. Some say that creative new ways of practicing agriculture—including some we haven’t yet even imagined—may allow us to have our fuel and eat our food, too. But few question the papers’ theses.  So what is the carbon impact of biofuels? The answer depends upon a slew of unknowns. Will technological advances reduce the production cost of more environmentally friendly biofuels to the point of commercial competitiveness? Can these fuels be grown benignly if market forces offer higher profits when environmental constraints are ignored? Will improvements in yields, conversion efficiencies, and fuel mileage reduce the demand for liquid fuels to the point where biofuels produced on lands not suited for food crops can fuel the world’s demand for transportation? Will civilization show the political will and the regulatory ingenuity to resist the temptation to exploit wild lands for feedstock production when commodity prices spike? Can people change their lifestyles to further reduce demand for farmland? These are the kinds of big questions that will determine whether biofuels help create a sustainable future or an environmental debacle.

The Carbon Footprint of Biofuels: Can We Shrink It Down to Size in Time?