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Double-Counting in Life Cycle Calculations


Address correspondence to:
Manfred Lenzen
ISA, A28
University of Sydney NSW 2006


Many popular frameworks apply life cycle calculations to examine environmental burdens occurring throughout the life cycle of products and services that are either purchased by final consumers or demanded as inputs by producers. Accounting for the full supply chain of producer items can lead to double-counting effects when results of separate studies are added up and referenced or compared to totals. If, for instance, energy life cycle inventories were prepared for all consumer and producer items in an economy and added up, the resulting total amount of energy would be greater than national energy consumption. Although this double-counting is inconsequential if analyses are appraised in isolation without reference to national totals, it leads to serious errors when large interconnected systems are analyzed or when results are placed into wider (e.g., regional, national, or global) contexts. The article lists a number of prominent policy and decision-making frameworks that make use of life cycle techniques, where this double-counting error is highly undesirable. It proposes a solution to the double-counting problem in which supply chains in the product life cycle are split and burdens shared between the supplying and demanding sides of every transaction in the economy.