Biofuels: Threats and Opportunities It is possible to make biofuels that reduce carbon emissions, but only if we ensure that they do not lead to additional land clearing. When land is cleared for agriculture, carbon that is locked up in the plants and soil is released through burning and decomposition. The carbon is released as carbon dioxide, which is an important greenhouse gas, and causes further global warming. Converting rainforests, peatlands, savannas, or grasslands to produce food crop–based biofuels in Brazil, Southeast Asia, and the United States creates a “biofuel carbon debt” by releasing 17 to 420 times more carbon dioxide than the annual greenhouse gas reductions that these biofuels would provide by displacing fossil fuels. Depending on future biofuel production, the effects of this clearing could be significant for climate change: globally, there is almost three times as much carbon locked up in the plants and soils of the Earth as there is in the air and 20% of global carbon dioxide emissions come from land use change. Global demand for food is expected to double in the next 50 years and is unlikely to be met entirely from yield increases, thus requiring significant land clearing. If existing cropland is insufficient to meet imminent food demands, then any dedicated biofuel crop production will necessarily create demand for additional cropland to be cleared. Several forms of biofuels do not cause land clearing, including biofuels made from algae, from waste biomass, or from biomass grown on degraded and abandoned agricultural lands planted with perennials. Present Generation of Biofuels: Reducing or Enhancing Greenhouse Gas Emissions? Previous studies have found that substituting biofuels for gasoline will reduce greenhouse gasses because growing the crops for biofuels sequesters takes carbon out of the air that burning only puts back, while gasoline takes carbon out of the ground and puts it into the air. These analyses have typically not taken into consideration carbon emissions that result from farmers worldwide converting forest or grassland to produce biofuels, or that result from farmers worldwide responding to higher prices and converting forest and grassland into new cropland to replace the grain (or cropland) diverted to biofuels. Our revised analysis suggests that greenhouse gas emissions from the land use changes described above, for most biofuels that use productive land, are likely to substantially increase over the next 30 years. Even advanced biofuels from biomass, if produced on good cropland, could have adverse greenhouse gas effects. At the same time, diverting productive land raises crop prices and reduces consumption among the 2.8 billion people who live on less than $2 per day. Simply avoiding biofuels produced from new land conversion – as proposed by a draft European Union law -- does not avoid these global warming emissions because the world’s farmers will replace existing crops or cropland used for biofuels by expanding into other lands. The key to avoiding greenhouse gas emissions and hunger from land use change is to use feedstocks that do not divert the existing productive capacity of land – whether that production stores carbon (as in forest and grassland) or generates food or wood products. Waste products, including municipal and slash forest waste from private lands, agricultural residues and cover crops provide promising opportunities. There may also be opportunities to use highly unproductive grasslands where biomass crops can be grown productively, but those opportunities must be explored carefully. Biofuels and a Low-Carbon Economy The low-carbon fuel standard is a concept and legal requirement in California and an expanding number of states that targets the amount of greenhouse gases produced per unit of energy delivered to the vehicle, or ca