engleski

The implicit boundary conditions of attributional and consequential LCA

In both attributional and consequential system modelling, fundamental assumptions are implied on what unit processes to include in the product systems, but these assumptions are typically not made explicit. The extent of unit processes included in a product system is fundamentally dependent on the leakage in the studied supply chain, i.e. the extent to which the initial reference flow is lost to the system environment in each step of the supply chain. If there was no leakage, an attributional product system would include all unit processes since the start of human civilisation, and a consequential product system would include all consequences to the end of human civilisation. In practice, leakage provides a clear boundary condition for both attributional and consequential system modelling. In system models that are based on an economic definition of the supply chain, the leakage occurs in each step in the supply chain due to the payment of labour, tax, profit and rent (also known as primary factors). The unit processes in a revenue allocated system are thus limited to those that contribute to the life cycle costs of the studied reference flow. And the unit processes included in a consequential system are limited to those that react to the marginal change in income resulting from the spending on the reference flow, corresponding to the first order effects of this spending. Implicitly, a consequential model does not include second order effects, i.e. the changes in consumption patterns that may result from the redistribution of the initial spending on the population groups that receive the primary factor income, nor does it include the second order effects of stimulating specific activities, e.g. from research and technological development. Such multiplier effects can be – and are – included in dynamic economic models for the study of societal developments, but this goes beyond the normal first order, steady-state, small-scale perspective of consequential LCA. When a consequential model is used to compare two products with different prices, the monetary balance of the combined system can only be maintained by adding the first order price rebound effect. The described implicit boundary condition thus provides a clear rationale for and delimitation of the rebound effect to be included. For attributional models with other allocation keys than revenue, leakage also occurs, but with the additional complication that allocation properties that are also present in waste and emissions needs to be taken into account.

Different Modes of LCA

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