The field of 'industrial ecology' was created to inform purposive human decision making about industrial production processes, especially as they impact the environment, by taking advantage of knowledge about the functioning of healthy ecosystems. These ecosystems are characterized by their vigor, maintenance of diversity, resilience, and relative stability over time. Other ecosystem properties seen as potentially desirable in industrial systems include minimal use of virgin materials and maximal use of renewable, biodegradable resources, minimal production of toxic waste products, and, more generally, sustainable use of resources. More recently the scope of industrial ecology has enlarged to include decision-making regarding consumption activities as well. Human decision-making is important because humans, while one species among many, are responsible for dramatic and far-reaching changes to the global environment and thus to the existence of other species.
Industrial ecology is not the only new, cross-disciplinary field employing the word 'ecology'. Among others utilizing the ecological metaphor are the ecology of the family, organizational ecology, and ecological economics (see Ecological Economics 1). In all cases the intention is to suggest that the field in question constitutes a complex system, in some instances with direct relations to biological ecosystems. The 'ecology of the family' focuses on how family members are shaped by their interactions, both competitive and mutualistic, with one another. 'Organizational ecology' applies population dynamics models to the births and deaths of firms and industries and examines how the evolution of organizational structure is shaped by competitive and cooperative interactions. 'Ecological economics' departs from the observation that natural ecosystems uninfluenced by human activity no longer actually exist: counting both economists and ecologists among its numbers, it attempts to integrate the two professional domains. Industrial ecology is distinctive in its focus on the industrial system, literally treating it as an ecosystem or, more exactly, the subsystem of principal interest within a more inclusive ecosystem. The flows of energy and material characterize an industrial system and serve as the integrating focus of all description, design, and analysis in industrial ecology. Not merely analogous to the flows of energy and material in ecosystems, they actually constitute those flows. The production and consumption activities of humans can be described in terms of these flows just like the activities of any other animal. Given this focus on industrially valuable resources, it is not surprising that most of the field's founders were engineers or applied physical scientists with interests in chemical processes and effluents and, more generally, the reduction, reuse, and recycling of industrial wastes.
Industrial ecology is motivated by its concern for the well-being of the environment. As the inclusion of ecology in its name indicates, it puts special emphasis on developing and implementing solutions and policies at the system level, up to and including the global system. Central to the system perspective is the concept that the behavior of individual components cannot be fully understood without reference to the system in which they interact. Industrial ecology explicitly recognizes that human industrial activities in the modern industrialized world are characterized by the interdependence of many industries, each industry itself often performing many interconnected production processes, all reliant on inputs of energy and materials and discharging wastes.
System scientists have long understood that the basic features of a system of interacting components need to be understood in a top-down fashion, even though many processes operate at the level of component parts. In the case of system design, top-down and bottom-up contributions generally proceed in an iterative fashion. This system perspective influences the direction that industrial ecology takes in confronting environmental challenges: improving the environmental compatibility of individual industrial processes is evaluated in the context of improving the overall industrial system. A simple illustration is provided by Figure 1, which combines two waste streams, fly ash from coal-fired power plants and waste plastic from plastic manufacturing, into a useful product, light-weight building blocks. At the same time the waste heat and carbon dioxide from the power plant can be supplied to a large-scale greenhouse, leading to increased production of fruits and vegetables. These are both examples of'open loop' waste reuse. ('Closed loop' use of waste is represented in Figure 1 by the recycling of waste plastics by the plastics factory.) Reducing any of these waste streams might both increase the unusable waste from the others while also reducing the quantity of useful product. Interestingly, recognizing the value of waste as a resource is a major theme of industrial ecology.
The tracking of resources, intermediate products, final products, and wastes can be conducted at the level of business establishments, towns, nations, or in the context of nations interacting in the global economy. The analysis of these flows, as a basis for action, can also take place at all these levels.
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