unless coordinated, the data do not fully support existing metrics and limit the scope for future ones. Procedural changes aimed at synchronizing data collection among various federal departments and agencies to build a single base (year) would amplify the benefits of existing collection efforts. Equally important from an environmental perspective is the development of standardized definitions for classifying material commodities to erase confusion leading to omissions and double counting of material components.

Accurate data on wastes are the hardest to obtain. Companies collect little or no data for many waste streams due to the actual or perceived absence of economic value. High disposal costs and regulatory requirements have improved waste accounting practices at many firms, but wastes have yet to receive the respect that marketability confers. Among the main goals of industrial ecology is exploring potential markets for waste materials. Currently, the dearth of reliable information available for wastes is one of the factors blocking progress. Better information would improve the market climate for wastes and at the same time help to develop metrics that assess their relative impact nationally.

Although improved national environmental metrics go hand in hand with better databases, metrics are not meant simply to compile information. Their purpose is to embed the data in a context that recognizes the larger system and is relevant to how it works. Good environmental indicators exist, but too often remain detached from each other and from an unambiguous framework. Appropriate metrics should correlate individual indicators and clarify the relation of each one to the whole. To illustrate, citing fertilizer usage rates without reference to agricultural productivity is misleading and causes unwarranted alarm. Conversely, extolling the environmental virtue of a lighter consumer product without examining the life-cycle implications of its fabrication and disposal is premature. To enhance their value and minimize misuse, commentary and interpretation should accompany the publication of metrics.

To adequately respond to complex questions of environmental performance requires both context and an array of metrics. For example, is the nation beginning to "dematerialize," that is, effectively decouple overall materials consumption from continued economic growth? For the U.S. energy sector the answer has been in the affirmative. Efficiency gains and the shift away from heavy manufacturing have modified the traditional relation between energy consumption and economic growth in the United States. Single indicators (i.e., kilowatt hours consumed/$GDP) elegantly illustrate this development. To have similar confidence regarding materials will require a more elaborate set of measures that are sensitive to the diverse structure of contemporary materials use and the many forces affecting its dynamics (Wernick et al., 1996). National materials metrics would refine how such questions are articulated and provide the basis for more convincing answers than are now available.

Looking to the future, national materials metrics help order the national research agenda for materials science and engineering (National Academy of Sci-



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