IN THEIR REPORTS IN THE 29 FEBRUARY ISSUE (“LAND CLEARING AND THE BIOFUEL CARBON debt,” J. Fargione et al., p. 1235, and “Use of U.S. croplands for biofuels increases greenhouse gases through emissions from land-use change,” T. Searchinger et al., p. 1238), the authors do not provide adequate support for their claim that biofuels cause high emissions due to land-use change. The conclusions of both papers depend on the misleading premise that biofuel production causes forests and grasslands to be converted to agriculture. However, field research, including a meta-analysis of 152 case studies, consistently finds that land-use change and associated carbon emissions are driven by interactions among cultural, technological, biophysical, political, economic, and demographic forces within a spatial and temporal context rather than by a single crop market (1–3). Searchinger et al. assert that soybean prices accelerate clearing of rainforest based on a single citation (4) for a study not designed to identify the causal factors of land clearing. The study (4) analyzed satellite imagery from a single state in Brazil over a 4- year period and focused on land classification after deforestation. Satellite imagery can measure what changed but does little to tell us why. Similarly, Fargione et al. do not rely on primary empirical studies of causes of landuse change. Furthermore, neither fire nor soil carbon sequestration was properly considered in the Reports. Fire’s escalating contribution to global climate change is largely a result of burning in tropical savannas and forests (5, 6). Searchinger et al. postulate that 10.8 million hectares could be needed for future biofuel, a fraction of the 250 to 400 million hectares burned each year between 2000 and 2005 (5, 6). By offering enhanced employment and incomes, biofuels can help establish economic stability and thus reduce the recurring use of fire on previously cleared land as well as pressures to clear more land (7–9). Neither Searchinger et al. nor Fargione et al. consider fire as an ongoing land-management tool. In addition, deep-rooted perennial biofuel feedstocks in the tropics could enhance soil carbon storage by 0.5 to 1 metric ton per hectare per year (10). An improved understanding of the forces behind land-use change leads to more favorable conclusions regarding the potential for biofuels to reduce greenhouse gas emissions.

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Keith L. Kline
Virginia H. Dale
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