Revealing hidden CO2 impacts from consequential consumption by matrix analysis: Application to Japanese single households

Abstract

The aim of this study was to develop a novel analytical framework using matrix-based analysis, to visualize the environmental impacts of consumption, by considering the direct and indirect consumption of all the items induced by the initial consumption (called “consequential consumption”), in the context of consequential life cycle assessment (LCA). The significance of this framework and the importance of considering consequential consumption have been demonstrated by analyzing the net CO2 emissions due to consumption, through a case study of single households in Japan.The analytical framework includes the following four steps: (1) categorization of consumers, (2) calculation of a matrix of consequential consumption, (3) impact assessment, and (4) uncertainty analysis. The normalization process plays an essential role in the calculation of a matrix of consequential consumption, while meeting the constraint of fixed income. The matrix of consequential consumption was obtained by analyzing the latest Japanese household expenditure data for 2004. The net CO2 emission from consumption was estimated using the matrix of consequential consumption and the CO2 intensities of products/services in Japan.As a result, we found that the consumption of some products/services have the potential to increase/decrease CO2 emissions beyond their own CO2 intensities, because of consequential consumption. In spite of their relatively small CO2 intensities, several products and services (meat, dairy products and eggs, oils, fats and condiments, water and sewerage charges, domestic nondurable goods) have high net CO2 emissions per unit price (Japanese yen; JPY). This is because of high CO2 emissions from the consequential consumption of energy. In contrast, the net CO2 emission from charges for board are negative because of the substitution relationship between food and energy items. Compared with the results of other foregoing studies on food materials, the net CO2 emission by our approach is much larger than that indicated by the conventional process-specific approach.