Glossary
Life Cycle Assessment (LCA):
Life Cycle Assessment is a modelling approach aimed at quantifying the environmental (and sometimes social) impacts of products, services, and/or decisions. It considers the entire production chain, from the extraction of primary resources to waste treatment.
The approach is framed by ISO standards and developed by a large interdisciplinary scientific community, working both on the accounting of economic and material flows and on the causal chains linking emissions to impacts on ecosystems and human health. LCA focuses on the impacts associated with a function, which is represented by the functional unit. Typically, one would model the impact associated with “1 km travelled in an electric car” or “1 km travelled in a conventional (internal combustion) car”—two different ways of fulfilling the same function: travelling one kilometre.
It is LCA—often simplified and sometimes modified (!)—that underlies many of the environmental impact scores displayed on certain products.
Attributional and Consequential LCA:
Life Cycle Assessment (LCA) actually encompasses several methodological approaches. The most important distinction is between attributional LCA (A-LCA) and consequential LCA (C-LCA).
These two approaches address different questions and rely on two distinct understandings of what an “impact” is.
A-LCA aims to determine the share of the overall level of impact that can be attributed to a given product or service. It adopts a retrospective approach, examining the economic activities that were necessary to provide the product or service
under consideration. However, the same economic activities often produce several products, and more broadly all flows are interconnected within the economy. As a result, it is impossible to objectively define a way to isolate only the flows specifically linked to the final product being studied. A simple “snapshot” of the production history is therefore not sufficient to isolate the impact of a product. To address this, A-LCA relies on allocation rules to distribute responsibility for impacts among the different products generated by a given activity.
For example, a dairy farm produces both milk and meat. Cows emit methane, and the barn consumes electricity. What share of the methane emissions and electricity use—and their associated impacts—should be attributed to the meat and to the milk? In such cases, allocation rules are used to distribute impacts between co-products. In this sense, A-LCA provides a snapshot, at a given moment, of the economic and environmental flows associated with a product. It then uses a set of rules to attribute responsibility for these flows to the final product.
C-LCA, by contrast, starts from the idea that it is impossible to objectively assign a share of impacts to a product. Instead, it proposes to think about impacts in a more dynamic way. Impacts are not intrinsic attributes of products themselves, but the result of decisions that set the productive system in motion.
For instance, when you buy a bottle of milk, the impacts associated with producing that bottle have already occurred; they are not caused by your purchase. However, your purchase sends a signal of demand. The store orders the next bottle, generating additional demand, and the market responds by extending or maintaining certain production capacities, leading to future emissions.
The objective is therefore no longer to attribute a share of past impacts to the bottle of milk in your hand, but to model how the demand signal associated with a decision triggers responses within the production system. In this perspective, an impact is understood as a change in the state of the system, and the focus is placed on the consequences of decisions.
These two schools therefore correspond to fundamentally different philosophies, and they can produce very different results because they are not asking the same question.
Other “subtypes” of LCA also exist. These approaches can generally be used withineither of the two major schools.