The Model Linkages Analysis peer review specifically solicited feedback on the following topics: the use of multiple models and data sources, specifically in regards to land-use impacts; use of models for each component of the analysis, particularly the agricultural, petroleum, and energy sectors; and the use of the results of the models together, particularly in regards to the FASOM and FAPRI models, upstream greenhouse gas (GHG) emission factors, electricity production modeling, and fuel and feedstock transport.
Energy Independence and Security Act Mandate
The United States Environmental Protection Agency (EPA) has undertaken a lifecycle assessment of GHG emissions associated with increased renewable fuels production as part of the proposed revisions to the National Renewable Fuel Standard program. The Energy Independence and Security Act (EISA) of 2007 set the first-ever mandatory lifecycle GHG reduction thresholds for renewable fuel categories. EISA 2007 specifies that EPA’s lifecycle analysis must to take into account GHG emissions “related to the full fuel lifecycle, including all stages of fuel and feedstock production and distribution,” including “direct emissions and significant indirect emissions such as significant emissions from land-use changes.” In addition, EISA 2007 requires EPA to determine which biofuel production pathways reduce GHG emissions by the required threshold amounts relative to the 2005 petroleum baseline.
Indirect and Direct Emissions in the Lifecycle Analysis
The definition of lifecycle analysis set forth in EISA 2007 includes both direct and indirect emissions related to the full fuel lifecycle. EPA defined direct emissions as those that are emitted from each stage of the full fuel lifecycle, and indirect emissions as those emitted from second-order effects that occur as a consequence of the full fuel lifecycle.The definition of indirect emissions specifically includes “land-use changes” such aschanges between forest, pasture, savannah, and crop land types. Most of the charge questions in this peer reviewer are concerned with relationships between model linkages and indirect effects, both for the petroleum baseline and the renewable fuels emissioncalculations.
Description of FASOM, FAPRI and GREET
To date, no single model adequately accounts for domestic and international, as well as direct and indirect emissions associated with renewable fuels. Therefore, in order to conduct the lifecycle assessment of biofuel production in accordance with the standards set forth by EISA 2007, EPA employed a set of models, each best suited to simulating a particular component of the analysis. On the domestic side, EPA used the Forestry and Agriculture Sector Optimization Model (FASOM) in order to simulate changes in domestic crop prices, agricultural land-use and crop export volumes. FASOM’s simulated crop exports link to the integrated Food and Agriculture Policy and Research Institute (FAPRI) models which then simulates agricultural market changes and land-use change internationally. A third model, the Greenhouse Gases, Regulated Emissions, and Energy Use in Transportation (GREET) model was used to quantify the emissions factors associated with different steps of the production and use of various fuel types. GREET also estimates the GHG emissions associated with electricity production required for biofuels and petroleum fuel production. For the agricultural sector, EPA also relied upon GREET to provide GHG emissions associated with the production and transport of agricultural inputs such as fertilizer, herbicides,and pesticides. Domestic agricultural sector GHG emissions are estimated by FASOM. FAPRI results were converted to GHG emissions based on GREET defaults and IPCC emission factors.
Renewable Fuels Standard Model Linkage Methodology
To quantify the lifecycle GHG emissions associated with increased domestic biofuels production, EPA compared the impacts of renewable fuels under the EISA mandate to a reference case without EISA. Since it was not practical to conduct an analysis for every year, EPA chose to conduct the analysis using the final year of the Renewable Fuel Standards when they are fully phased in, or 2022.
Secondary Energy Sector Impacts Modeling
EPA conducted significant modeling of the petroleum and energy sectors in order properly compare GHG emissions resulting from the lifecycle of biofuels with those resulting from the lifecycle of petroleum-based fuels. Certain aspects of the secondary energy sector impacts modeling and the petroleum sector modeling were subject to discussion in this review.

By: ICF International

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