Uncertainty in Life Cycle Greenhouse Gas Emissions from United States Coal

Coal is an abundant energy resource, consumed in the United States chiefly by the power generation sector. Due to potential energy security benefits, it has also been considered as an alternate source for gasoline and diesel production. Life cycle assessment (LCA) studies have previously estimated the greenhouse gas emissions associated with coal combustion as well as upstream activities such as mining and transport, to compare its environmental impact with other fuels. Until recent years, LCA studies predominantly ignored the uncertainty and variability inherent in life cycle assessment. More recent work has estimated the uncertainty in the life cycle inventories of fossil fuels, but the use of these uncertainty ranges to model system-wide impacts has been limited. As shown by previous studies, uncertainty often affects the conclusions of comparative life cycle assessments, especially when differences in average environmental impacts between two competing fuels/products are small. This study builds upon an existing deterministic life cycle framework for coal and develops uncertainty estimates of associated greenhouse gas emissions, with the objective of supporting more robust decision-making in comparative energy systems analyses involving coal. Greenhouse gas emissions from fuel use and methane releases at coal mines, fuel use for coal transport and combustion of coal, based on publicly available data are included in the life cycle framework. Mean life cycle GHG emissions from coal are estimated to be 96 g CO(2)e/MJ, while the 90% confidence interval ranged between 89 and 106 g CO(2)e/MJ. Life cycle greenhouse gas emissions from Fischer-Tropsch (FT) coal-based gasoline are stochastically compared to emissions from petroleum-based gasoline. In the base case modeled, emissions from coal-based FT gasoline were found to be higher than emissions from petroleum-based gasoline with a probability of 80%, while they are lower with a probability of 20%. Results suggest that incorporating uncertainty in life cycle estimates is important, especially if these estimates are to be used within policy frameworks.