Low Carbon Fuel Emissions Modeling Mired in Debate

By Published On: February 15, 2008

California’s efforts to develop a low carbon fuel standard are embroiled in an arcane, but high stakes debate. The controversy is over how to calculate greenhouse gas emissions attributable to automotive fuels from the oil and corn fields where they originate to the vehicle engines where they are burned. The complex question of how to effectively measure and model so-called life cycle emissions from a wide variety of competing fuels has become urgent as California Air Resources Board regulators race to fashion and adopt a low carbon rule for transportation fuels by the end of the year. Decisions they make in the coming months promise to make a huge difference in the energy future of California and the nation. Their analysis, for instance, is likely to determine whether the standard gives rise to plug-in hybrid electric vehicles backed by electric utilities, or to a major expansion of the ethanol industry. The outcome also could impact the state’s much vaunted climate change law, AB 32. The low carbon fuel standard is expected to cut greenhouse gas emissions in California by up to 20 million tons a year by 2020, about 11 percent of the total reductions called for under the law. If it falls short, regulators may have to turn to other sources of emissions—like the power industry—to make up the difference. “It’s a very dynamic process,” said John Courtis, Air Board manager of alternative fuels. “Our intentions are multi-dimensional.” At issue is whether corn-based ethanol, soy-based biodiesel, and other crop-based fuels actually produce more or less greenhouse gas emissions over their life cycle than petroleum-based fuels. The Air Board faces increasing pressure and mounting studies indicating that biofuels made with crops once destined for the kitchen table are increasing carbon dioxide emissions by triggering far-flung land-use changes. The studies—the latest published last week in Science (see the “Energy Matters” column on page 12 for details)—say that farmers are clearing land to replace the food crops now being turned into ethanol. This releases a torrent of carbon to the air. Courtis said the Air Board wants to account for land-use changes that occur with the introduction of biofuels. However, to do so he noted that the Air Board first has to fashion a “transparent” model for assessing emissions associated with those changes. It also must gain some degree of consensus on the assumptions behind the model among the many stakeholders in the low carbon fuel proceeding, he added. They include oil companies, ethanol producers, farmers, utilities, auto companies, environmental justice advocates concerned about rising food insecurity, and myriad others. “In reality, we just simply do not know what will happen,” said Michael Wang, Argonne National Laboratory systems assessment section leader who developed the GREET model, which has become the gold standard of emissions modeling for fuels. “We don’t have the modeling capabilities to address these questions.” GREET stands for Greenhouse Gases, Regulated Emissions, and Energy Use in Transportation. Unfortunately, Wang said, the Air Board faces an “onerous time situation” and may have to make some quick assumptions about emissions from land-use changes that occur when biofuels produced from a variety of feedstocks are introduced. However, with the explosive growth of the corn-based ethanol industry, Wang said that the question of land-use changes has become too important to ignore. Yet, the version of the GREET model California regulators used in initially modeling emissions from different fuels does not account for land-use changes, according to Courtis. To rectify that deficiency, the Air Board is studying various models it could use in conjunction with GREET to answer the question of how crop-based biofuels change land-use and associated greenhouse gas emissions. These include release of carbon dioxide from plants and soil when land is cleared for farming, as well as changes in releases of nitrous oxides. Courtis said that the Air Board plans to lay out assumptions for modeling land-use changes late this month and review models for assessing those changes in March and April. It plans to present its ideas in public and seek comment from stakeholders before moving forward with a modeling analysis of different fuels that incorporates land-use changes. It hopes to develop a draft low carbon fuel standard by this summer. Editor’s note: For a more detailed report of the low carbon modeling debate, please see our sister publication E=MC2- Energy Meets Climate Challenge. You can find it at www.energymeetsclimate.com

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