Life Cycle Analysis of Biofuels Jason Hill, University of Minnesota, St Paul, MN, USA r 2013 Elsevier Inc All rights reserved Glossary Biofuel Liquid transportation fuels derived from plants or other biological materials Carbon footprint Life cycle analysis in which climate change is the impact category of concern Functional unit Quantity of reference for comparing two or more products based on their equivalent use Life cycle analysis Method of quantifying the suite of environmental effects associated with the production and use of a given product Introduction Life cycle analysis (LCA), also known as life cycle assessment, is a method of quantifying the environmental impact of products such as biofuels In LCA, researchers prepare an inventory of the resources used (e.g., fossil fuels and raw materials) and the substances generated (e.g., greenhouse gases, solid waste, and other pollutants) throughout the full life cycle of the production, transport, and use of the product of interest From this inventory, researchers prepare an impact assessment that estimates the ultimate effects on human health, ecosystem function, and natural resource depletion Because LCA considers the entire product life cycle, it is useful both in identifying major sources of environmental impact in a product’s supply chain and in mitigating them (Graedel, 1996; Curran, 2008) The first LCA study is widely held to have been conducted in 1969 by Teasley, who was examining different beverage container options for the Coca-Cola Company (Hunt and Franklin, 1996) To this day, LCA is predominantly used as a comparative tool by corporations, marketers, regulators, and consumers for making informed choices Liquid transportation biofuels are typically compared against conventional petroleum-derived fuels such as gasoline, diesel, and aviation fuels (Farrell et al., 2006; Stratton et al., 2011) Comparisons are also made between biofuels and alternative uses for biomass such as bioelectricity (Campbell et al., 2009; Ohlrogge et al., 2009) Types Various methods for conducting LCA exist, each of which has particular strengths and limitations One major albeit subtle distinction lies in whether the goal of an LCA study is to assign responsibility for environmental impacts to a given product or whether the goal is to estimate the net change in environmental impacts as a result of a decision to produce a product (Finnveden et al., 2009) The first of these, commonly known as an attributional approach, takes the total environmental Encyclopedia of Biodiversity, Volume Market-mediated effect Changes in the supply and demand of other products due to the production of a given product Supply chain Those stages in the production and use of a given product through which materials and energy flow and can be traced System boundary The set of processes under consideration in a given life cycle analysis impact of human activity and seeks to ascribe responsibility for a portion of it to a given product, which may include its entire supply chain or selected parts of it (Weidema, 2003) The second, commonly known as a consequential approach, takes the total environmental impact of human activity and seeks to understand how it expands and contracts as a result of producing and using a given product (Earles and Halog, 2011) An attributional LCA is, therefore, arbitrarily defined as a function of how system boundaries are drawn, typically limited by space, time, or stage in a supply chain It is of primary use to engineers looking to improve process efficiencies or to marketers comparing among purchase options Alternatively, consequential LCA has infinite system boundaries, which is essentially the same as saying there are no system boundaries It is strictly defined as the entire suite of direct and indirect impacts, regardless of where or when they occur It is of primary use to policy makers and regulators who are concerned with the cumulative and comprehensive effects of product decisions Attributional LCA is typically conducted using processbased models, input–output models, or a hybrid of the two Process-based models measure environmental flows along a given supply chain, including processes flowing therein and therefrom Process-based models offer a fine resolution and product-specific results but typically have narrow system boundaries so as to be tractable and representative of the supply chain under which corporate control may be exerted By contrast, input–output models utilize data both on trade among sectors and the environmental impact of each of these sectors to allocate environmental impact to a product produced in a given sector (Leontief, 1970; Lave et al., 1995) These models offer much broader system boundaries (e.g., the entire economy of a nation) but present a coarser view, leaving the impact of a product unresolved within a given sector Hybrid approaches also exist that supplement product specific data from process-based models with data from the expanded system boundaries of input–output models (Suh and Huppes, 2005) Consequential LCA is methodologically similar to hybrid attributional LCA but with some key differences (Ekvall and http://dx.doi.org/10.1016/B978-0-12-384719-5.00365-8 627