20. D. W. Sample, thesis, University of Wisconsin(1989).21. D. J. Parrish, J. H. Fike, Crit. Rev. Plant Sci. 24, 423(2005).22. R. L. Graham, R. Nelson, J. Sheehan, R. D. Perlack,L. L. Wright, Agron. J. 99, 1 (2007).23. T. Searchinger et al., Science 319, 1238 (2008).24. R. Hammerschlag, Environ. Sci. Technol. 40, 1744(2006).25. B. D. Solomon, J. R. Barnes, K. E. Halvorsen, BiomassBioenergy 31, 416 (2007).26. D. J. Graham, S. Glaister, J. Transport Econ. Policy 36,1 (2002).27. T. Sterner, Energy Policy 35, 3194 (2007).28. Y. Malhi et al., Science 319, 169 (2008).29. R. E. Gullison et al., Science 316, 985 (2007).30. Supported by the University of Minnesota ’s Initiative forRenewable Energy and the Environment, NSF grant no.DEB0620652, Princeton Environmental Institute, and theBush Foundation. We thank T. Searchinger for valuablecomments and insights and J. Herkert for providingreferences.Supporting Online Materialwww.sciencemag.org/cgi/content/full/1152747/DC1Materials and MethodsTables S1 and S2References8 November 2007; accepted 24 January 2008Published online 7 February 2008;10.1126/science.1152747Include this information when citing this paper.Use of U.S. Croplands for BiofuelsIncreases Greenhouse Gases ThroughEmissions from Land-Use ChangeTimothy Searchinger,1* Ralph Heimlich,2R. A. Houghton,3Fengxia Dong,4Amani Elobeid,4Jacinto Fabiosa,4Simla Tokgoz,4Dermot Hayes,4Tun-Hsiang Yu4Most prior studies have found that substituting biofuels for gasoline will reduce greenhousegases because biofuels sequester carbon through the growth of the feedstock. These analyseshave failed to count the carbon emissions that occur as farmers worldwide respond to higherprices and convert forest and grassland to new cropland to replace the grain (or cropland)diverted to biofuels. By using a worldwide agricultural model to estimate emissions fromland-use change, we found that corn-based ethanol, instead of producing a 20% savings, nearlydoubles greenhouse emissions over 30 years and increases greenhouse gases for 167 years.Biofuels from switchgrass, if grown on U.S. corn lands, increase emissions by 50%. Thisresult raises concerns about large biofuel mandates and highlights the value of usingwaste products.Most life-cycle studies have found thatreplacing gasoline with ethanol mod-estly reduces greenhouse gases (GHGs)if made from corn and substantially if made fromcellulose or sugarcane (1–7). These studies com-pare emissions from the separate steps of grow-ing or mining the feedstocks (such as corn orcrude oil), refining them into fuel, and burningthe fuel in the vehicle. In these stages alone(Table 1), corn and cellulosic ethanol emissionsexceed or match those from fossil fuels and there-fore produce no greenhouse benefits. But becausegrowing biofuel feedstocks removes carbon di-oxide from the atmosphere, biofuels can in theor yreduce GHGs relative to fossil fuels. Studies as-sign biofuels a credit for this sequestration effect,which we call the feedstock carbon uptake credit.It is typically large enough that overall GHG emis-sions from biofuels are lower than those fromfossil fuels, which do not receive such a creditbecause they take their carbon from the ground.For most biofuels, growing the feedstock re-quires land, so the credit represents the carbonbenefit of devoting land to biofuels. Unfortunate-ly, by excluding emissions from land-use change,most previous accountings were one-sided be-cause they counted the carbon benefits of usingland for biofuels but not the carbon costs, thecarbon storage and sequestration sacrificed bydiverting land from its existing uses. Withoutbiofuels, the extent of cropland reflects the de-mand for food and fiber . To produce biofuels,farmers can directly plow up more forest or grass-land, which releases to the atmosphere much ofthe carbon previously stored in plants and soilsthrough decomposition or fire. The loss of matur-ing forests and grasslands also foregoes ongoingcarbon sequestration as plants grow each year,and this foregone sequestration is the equivalentof additional emissions. Alternatively , farmers candivert existing crops or croplands into biofuels,which causes similar emissions indirectly. Thediversion triggers higher crop prices, and farmersaround the world respond by clearing more forestand grassland to replace crops for feed and food.Studies have confirmed that higher soybean pricesaccelerate clearing of Brazilian rainforest (8). Pro-jected corn ethanol in 2016 would use 43% of theU.S. corn land harvested for grain in 2004 (1),overwhelmingly for livestock (9), requiring bigland-use changes to replace that grain.Because existing land uses already providecarbon benefits in storage and sequestration (or,in the case of cropland, carbohydrates, proteins,and fats), dedicating land to biofuels can poten-tially reduce GHGs only if doing so increases thecarbon benefit of land. Proper accountings mustreflect the net impact on the carbon benefit ofland, not merely count the gross benefit of usingland for biofuels. T echnically, to generate green-house benefits, the carbon generated on land todisplace fossil fuels (the carbon uptake cre dit) mustexceed the carbon storage and sequestration givenup directly or indirectly by changing land uses(the emissions from land-use change) (T ab le 1).Many prior studies have acknowledged butfailed to count emissions from land-use change be-cause they are difficult to quantify (1). One priorquantification lacked formal agricultural mod-eling and other features of our analysis (1, 10). Toestimate land-use changes, we used a worldwidemodel to project increases in cropland in all ma-jor temperate and sugar crops by country or re-gion (as well as changes in dairy and livestockproduction) in response to a possible increase inU.S. corn ethanol of 56 billion liters above pro-jected levels for 2016 (11, 12). The model’shis-torical supply and demand elasticities were updatedto reflect the higher price re gime of the past 3 yearsand to capture expected long-run equilibrium be-havior (1). The analysis identifies key factors thatdetermine the change in cropland.1) New crops do not have to replace all corndiverted to ethanol because the ethanol b y-product,dry distillers’ grains, replaces roughly one-thirdof the animal feed otherwise diverted.2) As fuel demand for corn increases andsoybean and wheat lands switch to corn, pricesincrease by 40%, 20%, and 17% for corn, soy-beans, and wheat, respectively. These increasesmodestly