Consequential LCA is a system modelling approach in which Activities in a Product system are linked so that activities are included in the product system to the extent that they are expected to change as a consequence of a change in demand for the Functional unit. This approach focuses on identifying and modelling the actual consequences that result from changes in production or consumption patterns, rather than simply describing current conditions.
The fundamental principle underlying consequential modelling is the question: "What activities in the economy will actually change if the demand for this product changes?" This forward-looking perspective distinguishes consequential LCA from attributional approaches, which allocate existing environmental burdens according to normative rules without necessarily considering market dynamics or system-wide responses to change.
In consequential modelling, system boundaries are determined by cause-and-effect relationships. When a product system changes, the model traces through the economy to identify which production activities will increase, which will decrease, and which will remain unaffected. This often involves identifying marginal or constrained suppliers, considering market dynamics, technological constraints, and economic relationships that determine how the broader system responds to changes in demand.
The consequential approach is particularly valuable for decision support contexts where the goal is to understand the implications of a specific choice or policy change. For example, when evaluating whether to increase production of a biofuel, consequential modelling would consider not only the direct production impacts but also the indirect effects on land use, displacement of other crops, and changes in production patterns elsewhere in the agricultural system.
This methodology stands in contrast to the attributional approach, which attributes environmental burdens based on physical or economic relationships without necessarily modelling system change. Whilst attributional LCA answers "what burdens are associated with this product?", consequential LCA answers "what will change if we alter demand for this product?"
