Introduction

Life-cycle assessment, or LCA, is an environmental accounting and management approach for assessing industrial systems. It considers all the aspects of resource use and environmental releases associated with a system, as defined by the function provided by a product, process, or activity. This cradle-to-grave approach considers all relevant impacts upstream and downstream of the consumer or producer. Specifically, LCA is a holistic view of environmental interactions that covers a range of activities, from the extraction of raw materials from the Earth and the production and distribution of energy, through the use, and reuse, and final disposal of a product (for simplicity, the word 'product' is used although the life-cycle concept applies equally well to processes and activities). LCA is a relative tool intended for comparison and not absolute evaluation, thereby helping decision makers compare all major environmental impacts when choosing between alternative courses of action (Figure 1).

LCA evaluates all stages of a product's life from the perspective that they are interdependent, meaning that decisions made at one point along the life cycle can have consequences somewhere else. LCA enables the estimation of the cumulative environmental impacts resulting from all stages in the product life cycle, often including impacts that go beyond the boundaries of traditional analyses. By including the impacts throughout the product life cycle, LCA provides a comprehensive view of the environmental aspects and a more accurate picture of the true environmental tradeoffs in product or process selection. A life-cycle

*The author is employed by the US Environmental Protection Agency's Office of Research and Development. This document has not been subjected to the agency's review and therefore does not necessarily reflect the views of the agency. No official endorsement should be inferred.

approach helps us recognize how our choices influence each point of the life cycle, so that we can balance potential tradeoffs and avoid shifting problems from one area to another, thereby positively impacting the overall environment. LCA is a way of thinking about the choices we make, when purchasing products, selecting materials, or identifying process alternatives by putting our decisions in context with facts related to all parts of the life-cycle system.

In connecting the different parts of the system, many LCAs lead to unexpected and nonintuitive results. For example, bio-based products, such as paper bags, paper cups, and cloth diapers, are not obviously superior in terms of using less energy and materials. Paper requires the harvesting and transportation of trees to pulp mills, activities which require energy. Paper making releases air pollutants and water discharges of chlorine and biological waste. After use, bags end up in landfills where they decay and release methane in the process. The amount of hot water needed to wash and dry cloth diapers is not inconsequential, especially for those who live where water is scarce or sewage is not treated. These kinds of analyses highlight how the environmental impacts of alternative products may lead to unanticipated consequences.

LCA identifies the potential transfer of environmental impacts from one media to another (e.g., eliminating air emissions by creating a wastewater effluent instead) and/or from one life-cycle stage to another (e.g., from use and reuse of the product to the raw material acquisition stage). If an LCA were not performed, the transfer might not be recognized and properly included in the analysis because it is outside of the typical scope or focus of product selection processes. By broadening study boundaries, LCA can help decision makers select the product or process that results in the least impact to the environment. This information can be used with other factors, such as cost and performance data, in the selection process.

Recycle

Recycle

Figure 1 Generic life-cycle stages (arrows represent transportation).

Figure 1 Generic life-cycle stages (arrows represent transportation).

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