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Life-cycle assessments attempt to summarize the environmental impacts of a product through its entire life-cycle, from the extraction of the raw materials through manufacturing, use, and disposal. Such information can serve as the basis of a search for design alternatives to reduce the environmental impact of a particular product or to compare several different technologies designed to serve the same function.
Although simple in principle, life-cycle analyses can be difficult to complete in practice because they require large amounts of information and frequently involve assessments of the relative importance of qualitatively different types of environmental impacts (Field and Ehrenfeld; Hocking, this volume). Comparing two alternatives that have qualitatively different environmental impacts is one situation in which collaboration between engineers and environmental scientists could be most useful. Engineers have the expertise to develop design options. Environmental scientists will have more information (although often not enough) about the environmental consequences of releasing different wastes. Even if it will never be possible to predict precisely how different design options will affect the environment, it seems self-evident that life-cycle analysts would benefit from the insights of ecosystem experts and that ecosystem experts would profit from an understanding of design options and production processes. If nothing else, such information could help set priorities for ecosystem research.
Field and Ehrenfeld elaborate on the difficulty of putting life-cycle assessment into practice. They explain the serious limitations that arise due to the inability to rank the importance of qualitatively different environmental impacts associated with different technologies or design alternatives. These limitations notwithstanding, the authors emphasize that life-cycle assessments help to illuminate the differences in the environmental properties of various technologies.
Hocking argues that the problem of ranking qualitatively different types of environmental impacts can be solved by using energy requirements as a basis for comparing different technologies or alternative designs. He notes that differences in the emissions characteristics of two technologies can often be overcome by the expenditure of energy to reduce the emissions of the poorer performing technology. He illustrates the insights that can result from an energy-based life-cycle analysis by comparing the energy requirements of ceramic, plastic, and paper cups.
Allenby and Graedel (this volume) focus on the extensive data requirements of conventional life-cycle analyses. They argue that if data requirements are too great, life-cycle analyses simply will not be performed. They choose instead a qualitative checklist approach and show how it can be used to guide the site selection and design of corporate facilities.
Todd (this volume) notes that Allenby and Graedel's decision-support matrix is the type of tool that many managers lack. Managers may wish to identify