emissions associated with various agricultural activities, such as CH4 emissions related to rice cultivation). With respect to energy use, LCA could be used to account for all of the various energy carriers across the total fuel cycle (e.g., transport fuels, electricity), as well as for upstream energy sources (e.g., feedstock for agricultural chemicals and fertilizers). With respect to which analytical approach to take, one could conduct either an attributional or consequential LCA, depending on the research question. (See the summary of Marty Heller’s presentation in Chapter 3 for descriptions of the two approaches.)
Defining System Boundaries and Unit of Analysis
While LCA extends across all stages, from feed to end-of-life (i.e., feed, farm operations, processing, retail, consumption, disposal or end-of-life), the analysis could be truncated so that only certain components are evaluated. For example, in a comparison of agricultural production methods, it would not be necessary to include product packaging. According to Keoleian, the group spent a great deal of time discussing the importance of defining the functional unit, that is, the basis of analysis (e.g., kilograms [kg] of meat, kg of protein, calories, total nutrition or diet), and the importance of defining the temporal and spatial boundaries of the analysis.
Effects to Consider
Many GHG emission and energy use effects are quantifiable. The “real issue,” Keoleian reported, is uncertainty. Many effects are difficult to accurately estimate. Keoleian described CO2 from fuel combustion, N2O from soils and manure, and CH4 from manure and enteric fermentation, all of which contribute to climate change, as important direct costs to consider; and CO2 sequestration resulting from certain types of land use changes (e.g., converting marginal land to rangeland) as a potential benefit to consider. Indirect land use change impacts can be important, but are difficult to quantify.
With respect to energy usage, Keoleian reported that British thermal units of primary energy consumption can be quantified “pretty well.” LCA can also be used to quantify impacts from air pollutant emissions associated with energy usage (e.g., NOx, PM, Hg, SO2 from coal combustion); water pollution (e.g., nitrate run-off from corn production, oil spills); and land use impacts such as biodiversity loss (e.g., from surface mining of coal).
Multiple working group participants emphasized several measurement challenges: