Type III industrial ecosystem.

energy reserves are adequate to support a rational and planned transition to sustainability. However, emissions from the use of such resources—particularly heavy metals and carbon dioxide—will have to be controlled if this potential is to be exploited in environmentally acceptable ways.

Probing deeper we find that this is but part of the answer. Duchin (in this volume) suggests that the geographic locus of emissions of carbon dioxide and oxides of sulfur and nitrogen will continue shifting from the rich to the poor economies, even if only moderate economic growth is achieved in developing countries over the next several decades. At the same time, there will be a significant increase in the total emissions of carbon dioxide. These shifts are likely to occur even under optimistic scenarios of accelerated adoption of modem, commercially proven technologies to reduce and control pollution in both rich and poor nations. Therefore, if emissions are to be held at current levels, significant changes in production and consumption practices will be required. In addition, strategies to improve industrial ecosystems in industrialized countries are likely to differ from those in developing nations.

Current industrial ecosystems can be characterized by a mix of Type I and Type II materials flows. Industrial cycles tend to be open, with little recycling. The Type III industrial ecology model, which most closely resembles natural ecosystems, is a "no waste" ecology. It is in keeping with the limiting goal of "zero discharge" adopted by several major companies. Yet, the elimination of manufacturing wastes, or zero discharge, is beyond the capability of modem technology and would require the full participation of consumers. It is probably an unattainable goal, but in pursuing that objective it is important to recognize that there are only two possible long-run fates for materials—dissipative loss and recycling or reuse. Recycle and reuse will therefore have to be a part of any quest for a zero-discharge industrial ecology.

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