Abstract
While debate on biofuels and bioenergy generally has sparked controversy over claimed greenhouse gas emissions benefits available with a switch to biomass, these claims have generally not taken into account indirect land use changes. Carbon emissions from land that is newly planted with biocrops, after land use changes such as deforestation, are certainly real β but efforts to measure them have been presented subject to severe qualifi cations. No such qualifications accompanied the paper by Searchinger et al. published in Science in February 2008, where the claim was made that a spike of ethanol consumption in the USA up to the year 2016 would divert corn grown in the USA and lead to new plantings of grain crops around the world to make up the shortfall, resulting in land use changes covering 10.8 million hectares and leading to the release of 3.8 billion tons of greenhouse gas emissions in terms of CO2 equivalent. These emissions, the paper argued, would more than offset any savings in emissions by growing biofuels in the first place; in fact they would create a βcarbon debtβ that would take 160 years to repay. Such criticism would be devastating, if it were valid. The aim of this perspective is to probe the assumptions and models used in the Searchinger et al. paper, to evaluate their validity and plausibility, and contrast them with other approaches taken or available to be taken. It is argued that indirect land use change effects are too diffuse and subject to too many arbitrary assumptions to be useful for ruleβmaking, and that the use of direct and controllable measures, such as building statements of origin of biofuels into the contracts that regulate the sale of such commodities, would secure better results. Β© 2009 Society of Chemical Industry and John Wiley & Sons, Ltd