Most prior studies have found that substituting biofuels for gasoline will reduce greenhouse gases because biofuels sequester carbon through the growth of the feedstock. These analyses have failed to count the carbon emissions that occur as farmers worldwide respond to higher prices 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 from land-use change, we found that corn-based ethanol, instead of producing a 20% savings, nearly doubles 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%. This result raises concerns about large biofuel mandates and highlights the value of using waste products.

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Use of U.S. Croplands for Biofuels Increases Greenhouse Gases Through Emissions from Land-Use Change

Negative environmental consequences of fossil fuels and concerns about petroleum supplies have spurred the search for renewable transportation biofuels. To be a viable alternative, a biofuel should provide a net energy gain, have environmental benefits, be economically competitive, and be producible in large quantities without reducing food supplies. We use these criteria to evaluate, through life-cycle accounting, ethanol from corn grain and biodiesel from soybeans. Ethanol yields 25% more energy than the energy invested in its production, whereas biodiesel yields 93% more. Compared with ethanol, biodiesel releases just 1.0%, 8.3%, and 13% of the agricultural nitrogen, phosphorus, and pesticide pollutants, respectively, per net energy gain. Relative to the fossil fuels they displace, greenhouse gas emissions are reduced 12% by the production and combustion of ethanol and 41% by biodiesel. Biodiesel also releases less air pollutants per net energy gain than ethanol. These advantages of biodiesel over ethanol come from lower agricultural inputs and more efficient conversion of feedstocks to fuel. Neither biofuel can replace much petroleum without impacting food supplies. Even dedicating all U.S. corn and soybean production to biofuels would meet only 12% of gasoline demand and 6% of diesel demand. Until recent increases in petroleum prices, high production costs made biofuels unprofitable without subsidies. Biodiesel provides sufficient environmental advantages to merit subsidy. Transportation biofuels such as synfuel hydrocarbons or cellulosic ethanol, if produced from low-input biomass grown on agriculturally marginal land or from waste biomass, could provide much greater supplies and environmental benefits than food-based biofuels.

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Environmental, economic, and energetic costs and benefits of biodiesel and ethanol biofuels

The Personal Interview

Hydrothermal technologies are broadly defined as chemical and physical transformations in high-temperature (200–600 °C), high-pressure (5–40 MPa) liquid or supercritical water. This thermochemical means of reforming biomass may have energetic advantages, since, when water is heated at high pressures a phase change to steam is avoided which avoids large enthalpic energy penalties. Biological chemicals undergo a range of reactions, including dehydration and decarboxylation reactions, which are influenced by the temperature, pressure, concentration, and presence of homogeneous or heterogeneous catalysts. Several biomass hydrothermal conversion processes are in development or demonstration. Liquefaction processes are generally lower temperature (200–400 °C) reactions which produce liquid products, often called “bio-oil” or “bio-crude”. Gasification processes generally take place at higher temperatures (400–700 °C) and can produce methane or hydrogen gases in high yields.

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Thermochemical biofuel production in hydrothermal media: A review of sub- and supercritical water technologies

Biofuels derived from low-input high-diversity (LIHD) mixtures of native grassland perennials can provide more usable energy, greater greenhouse gas reductions, and less agrichemical pollution per hectare than can corn grain ethanol or soybean biodiesel. High-diversity grasslands had increasingly higher bioenergy yields that were 238% greater than monoculture yields after a decade. LIHD biofuels are carbon negative because net ecosystem carbon dioxide sequestration (4.4 megagram hectare(-1) year(-1) of carbon dioxide in soil and roots) exceeds fossil carbon dioxide release during biofuel production (0.32 megagram hectare(-1) year(-1)). Moreover, LIHD biofuels can be produced on agriculturally degraded lands and thus need to neither displace food production nor cause loss of biodiversity via habitat destruction.

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Carbon-Negative Biofuels from Low-Input High-Diversity Grassland Biomass

To study the potential effects of increased biofuel use, we evaluated six representative analyses of fuel ethanol. Studies that reported negative net energy incorrectly ignored coproducts and used some obsolete data. All studies indicated that current corn ethanol technologies are much less petroleum-intensive than gasoline but have greenhouse gas emissions similar to those of gasoline. However, many important environmental effects of biofuel production are poorly understood. New metrics that measure specific resource inputs are developed, but further research into environmental metrics is needed. Nonetheless, it is already clear that large-scale use of ethanol for fuel will almost certainly require cellulosic technology.

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Supporting Online Material for: Ethanol Can Contribute To Energy and Environmental Goals

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Ethanol Can Contribute to Energy and Environmental Goals

This study describes how some biofuels are produced, emphasizing agricultural production systems, and considers what is needed in order to measure and communicate environmental performance, and gives examples of how this might be done. We describe a set of seven uses of a Green Biofuels Index, from a wholly market-driven implementation through a set of increasingly intrusive regulatory approaches. We then present several case studies of specific biofuel production pathways using a lifecycle analysis of the inputs to feedstock production and processing, but excluding market-mediated effects. We recommend four steps to create markets for green biofuels: 1. Measure the global warming intensity of biofuels. 2. Measure the overall environmental performance of biomass feedstock production. 3. Develop and implement a combined Green Biofuels Index. 4. Research better practices, assessment tools, and assurance methods.

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Creating Markets for Green Biofuels: Measuring and improving environmental performance - eScholarship

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Creating Markets for Green Biofuels: Measuring and improving environmental performance

Acknowledgements We would like to thank the Department of Water Resources and the State Water Plan Public Advisory Committee for giving us the opportunity to explore this issue. We thank Professors Margaret Taylor and Eugene Bardach for providing helpful comments and suggestions. We also wish to express our appreciation to who took the time to discuss this issue with us and explain their points of view. Finally, we are especially grateful to John Andrew and Michael Perrone for the time and attention they devoted to this project. and this report fulfills the course requirements of Public Policy 200. The opinions expressed in this report are those of the authors and do not necessarily represent those of the Goldman School, the University of California, or the Department of Water Resources. This study was prepared in conjunction with the 2003 update of the California Water Plan. Executive Summary The goal of this report is to provide a starting point from which the water planning community can move toward improving the allocation of water within the environmental sector. To facilitate that process, this report presents: 1) A discussion that highlights the water community's points of agreement on the concept of analyzing the application of water to the environment 2) A term, Managed Environmental Water Use Efficiency (MEWUE), to reflect that concept, and a definition of that term 3) A survey of existing methods that could be used to develop MEWUE 4) Suggestions about how to proceed with implementing MEWUE Based on our analysis, we found that there was genuine interest in understanding and improving how water is allocated to the environment. The idea of maximizing environmental benefits for a given amount of allocated water is a unifying thread among stakeholder interests. We focus on this idea throughout the report as the central concept that MEWUE is intended to achieve. We propose a new term to reflect the stated concerns of stakeholders that other terms, Environmental Water Use Efficiency and Ecosystem Restoration Water Use Efficiency, did not fully address. We propose Managed to indicate that MEWUE does not evaluate the environment's use of water per se but rather the effectiveness of water in controlled systems. We propose Environmental to reflect the range of " uses " of water in the ecosystem, including ecosystem maintenance, restoration, and water quality. Lastly, we support the use of the word Efficiency because efficiency communicates the intent of maximizing …

Brian T. Turner

Papers

Supporting Online Material for: Ethanol Can Contribute To Energy and Environmental Goals

Ethanol Can Contribute to Energy and Environmental Goals

Creating Markets for Green Biofuels: Measuring and improving environmental performance - eScholarship

Creating Markets for Green Biofuels: Measuring and improving environmental performance

Considering Water Use Efficiency for the Environmental Sector