Life Cycle Analysis and Temporal Distributions of Emissions: Limitations of Product-Centered Emission Analyses
AbstractAlthough the product-centered focus of life cycle analysis has been one of its strengths, thisanalytical perspective embeds assumptions that may conflict with the realities of the problems towhich it is applied. This paper demonstrates, through a series of mathematical derivations, thatall the products in use, rather than a single product, frequently should be the appropriate unit ofanalysis. Such a "fleet-centered" approach supplies a richer perspective on the comparativeemissions burdens generated by alternative products, as well as eliminating certain simplifyingassumptions imposed upon the analyst by a product-centered approach.A sample numerical case, examining the comparative emissions of steel-intensive and aluminumintensive automobiles, is presented to contrast the results of the two approaches. Thefleet-centered analysis shows that the "crossover time" (i.e., the time required before the fueleconomy benefits of the lighter aluminum vehicle offset the energy-intensity of the processesused to manufacture the aluminum in the first place) can be dramatically longer than thatpredicted by conventional life cycle analyses.The fleet-centered perspective explicitly introduces the notion of time as a critical element ofcomparative life cycle analyses and raises important questions about the role of the analyst inselecting the appropriate time horizon for analysis. Moreover, with the introduction of time as anappropriate dimension to life cycle analysis, the influences of effects distributed over time can bemore naturally and consistently treated.
Year of publication: |
2002-06-25
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Authors: | Field, Frank ; Kirchain, Randolph ; Clark, Joel |
Subject: | crossover time | product centered | fleet-centered |
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