Does hybrid LCA with a complete system boundary yield adequate results for product promotion?

Purpose: Hybrid life cycle assessment (LCA) with a complete system boundary is recognized as an advanced approach widely applied in comparative analysis with the goal of product promotion. Here, I evaluate the theoretical foundation, or assumptions, of hybrid LCA in this application and discuss alternative models. The goal of this article is partly to call attention to the restrictive assumptions involved in the models used in LCA and to instigate further research and effort to improve these models. Methods: As with process-based LCA, hybrid LCA is a type of linear model when it is used to estimate changes. It relies on several restrictive assumptions such as fixed input/output coefficients and unlimited supply of inputs. Besides, hybrid LCA further rests on the assumption of economy-wide effect, i.e., a change of any magnitude in the output of any product would affect the entire economy. This may be another restrictive assumption, and to what extent it is reasonable depends on an array of factors, including the product being studied, its role in the economy, the magnitude of change, and the structure of the economy. Results and discussion: Because of the restrictive assumptions, hybrid LCA may not necessarily yield adequate results for product promotion. This, however, does not mean that it entirely falls short, but that the assumptions need to be scrutinized and determined if they reasonably reflect the reality. If so, the results yielded by hybrid LCA may be adequate. But if not, the results fall short, and further research is needed. Conclusions: For comparative analysis with the goal of product promotion, understanding how increases in the output of the product being studied would affect the economy is crucial. And this should form the basis of decision making. Alternative models to consider for large-scale changes include computable general equilibrium models and rectangular choice of technology models, recognizing their limitations and assumptions as well. Alternatively, one may use simpler models such as process-based inventory but build scenarios to study how the impact of product promotion may ripple through the economy.