Life Cycle Assessment Methods4

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The impacts of a product (or process) on the environment come not only when the product is being used for its intended purpose, but also as the product is manufactured and as it is disposed of at the end of its useful life. Efforts to account for the full set of environmental impacts of a product, from production of raw materials through manufacture and use to its eventual disposition, are referred to as life-cycle analysis (LCA). LCA is an important tool for identifying opportunities for reducing GHG emissions and also for examining trade-offs between GHG emissions and other environmental impacts. LCA has been used to examine the GHG emissions and land use requirements of renewable energy technologies (e.g., NRC, 2009) and other technolo

4 This subsection was inadvertently left out of prepublication copies of the report.

gies that might reduce GHG emissions (e.g., Jaramillo et al., 2009, Kubiszewski et al., 2010, Lenzen, 2008, Samaras and Meisterling, 2008).

LCA of corn-based ethanol and other liquid fuels derived from plant materials (e.g., Davis et al., 2009; Kim et al., 2009; Robertson et al., 2008; Tilman et al., 2009) illustrate both the value of the method and some of the complexities in applying it. Because corn ethanol is produced from sugars created by photosynthesis, which removes CO2 from ambient air, it might be assumed that substituting corn ethanol for gasoline produced from petroleum would substantially reduce net GHG emissions. However, LCA shows that these emissions reductions are much smaller (and in some cases may even result in higher GHG emissions) when the emissions associated with growing the corn, processing it into ethanol, and transporting it are accounted for. A substantial shift to corn-based ethanol (or other biofuels) could also lead to significant land use changes and changes in food prices. LCA also points out the importance of farming practices in shaping agricultural GHG emissions and to the potential for alternative plant inputs, such as cellulose, as a feedstock for liquid fuels.

The utility and potential applications of LCA have been recognized by government agencies in the United States and around the world (EPA, 2010a; European Commission Joint Research Centre, 2010) and by the private sector. For example, Walmart is emphasizing LCA in the sustainability assessment it is requiring of all its suppliers.5 Useful as it is, LCA, like any policy analysis tool, has limitations. For example, the boundaries for the analysis must be defined, materials used for multiple purposes must be allocated appropriately, and the databases typically consulted to estimate emissions at each step of the analysis may have uncertainties. There is currently little standardization of these databases or of methods for drawing boundaries and allocating impacts. LCA may also identify multiple environmental impacts. For example, nuclear reactors or hydroelectric systems produce relatively few GHG emissions but have other environmental impacts (see, e.g., NRC, 2009d; NRC, 2009f), and it is not clear how to weight trade-offs across different types of impacts (but see Huijbregts et al., 2008). Finally, LCA is not familiar to most consumers and policy makers so its ultimate contribution to better decision making will depend on processes that encourage its use. These and other scientific challenges are starting to be addressed by the research community (see, e.g., Finnveden et al., 2009; Horne et al., 2009; Ramaswami et al., 2008); additional research on LCA would allow its application to an expanding range of problems and improve its use as a decision tool in adaptive risk-management strategies.

5 See http://walmartstores.com/Sustainability/9292.aspx.

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