Life Cycle Assessment
Life cycle assessment (LCA) is a technique for quantifying and calculating the environmental impacts associated with the production of a good on a life cycle basis (direct and indirect impacts). This involves defining boundaries of the system (project) and analyzing all of the inputs and material flows. The life cycle can be defined in many ways: A full life cycle is called cradle-to-grave, and it includes all of the environmental impacts associated with the production of a good from raw materials to disposal.
The product assessed can be anything from breakfast cereals to conventional petroleum fuels to drop in renewable jet fuel to chemicals or consumer electronics. LCA models calculate a range of environmental flows, including energy inputs, greenhouse gas emissions, air pollutants, water use, land use, eutrophication potential, photochemical ozone creation potential, abiotic depletion potential, acidification potential and others.
Most LCA models used for transportation fuels are spreadsheet-based and involve using an LCI database to calculate the environmental impacts associated with the material flows and inputs to a fuel value chain. LCA can be used to support fuel regulatory and/or legislative initiatives for renewable fuel targets, such as targets for greenhouse gas emission reductions. LCA is also used routinely in support of environmental claims made to business partners, customers and the public.
The steps to perform an LCA are outlined below.
- Define system boundaries by analyzing the processes of a specific production pathway
- Document all assumptions, process inputs, and details of data collection methods
- Perform model calculations and supply supporting documentation of process inputs and model operations
- Include analysis and calculations of co-products for any alternative pathways in the fuel production process
- Perform uncertainty and error analysis
The system boundary defines the approach to the analysis and it assures a consistent treatment for the case analyzed and the reference case. Diagrams are used identify which inputs and material flows are included in the accounting framework and which occur outside the scope of the analysis.
The approach to system boundary definition varies among models and studies. For example, the ARB LCFS identifies the system boundary for each fuel case while the EPA RFS2 uses a catch all system boundary diagram, similar to Figure 3.1, to reflect all biofuel pathways. EPA’s approach falls short of clarifying the process inputs and treatment of co-products. This lack of definition is especially important since components of the fuel life cycle are based on macro-economic estimates, average values, and projections for marginal inputs.
LCA can be broadly categorized as attributional or consequential LCA. An attributional analysis “attributes” sustainability metrics to a fuel pathway. This type of analysis provides useful information about the total impacts of the processes used to produce a fuel, but it does not consider indirect impacts arising from production; attributional analyses only consider impacts occurring within a product’s supply chain. An attributional LCA (ALCA) inventories and analyzes the direct environmental effects of some quantity of a particular product, including the direct effects of all required inputs and the direct effects of using and disposing of the product.
A consequential LCA (CLCA), in contrast, includes both direct and indirect effects of a production system, recognizing that all production is embedded within an economic system that adjusts in response to changes in production—and these adjustments produce additional environmental effects. Thus, consequential analysis includes both direct impacts occurring within a supply chain and indirect, market-induced changes occurring globally. CLCA is much larger in scope than ALCA and is accomplished with large uncertainty, due to the complexity of indirect impacts. The scope of CLCA includes total environmental impacts from fuel production (ALCA), plus all indirect effects that cascade over time resulting from economic effects.