Human impacts and industrial metabolism

Human economic activities have now reached an order of magnitude where their influence on the natural earth systems is quite significant. If we accept the analogy between biological and industrial metabolism, the latter can be defined as "the whole integrated collection of physical processes that convert raw materials and energy, plus labor, into finished products and wastes... with the economic system as the metabolic regulatory mechanism" (Ayres 1994). The firm (factory/plant) as a basic unit of the economic system can be compared to living organisms in biology. This analogy, taken a step further, leads into the notion of "industrial ecology."

Similarly, the "cycle" concept of the geo-scientists (e.g. the hydrological, carbon/oxygen, nitrogen, or sulphur cycles) can be adopted as "materials cycles" of the industrial system, starting with raw materials from the earth and returning them to nature as wastes (Ayres 1994). Industry converts primary resources into products useful for humans. In the course of these transformations, large amounts of waste are generated. It is important to measure these fluxes and processes. A number of measures of industrial metabolism have been proposed, which also require a sound knowledge of the biophysical basis. They include measurements of dissipative losses, of recycled materials, and also of the economic output per unit of material input, which can be called material productivity. Clearly, more exact measurements based on geophysical and geochemical data are desirable. This is because, collected at a sectoral level, they would allow improved analyses of the entire process of industrial metabolism. The establishment of an information system on industrial metabolism has been proposed (Fischer-Kowalski et al. 1993).

One attempt to introduce a universal measure for ecological disturbances is "materials intensity per unit of service" (Schmidt-Bleak 1992). The underlying idea is that the potential for disturbance is closely related to the mass of materials moved or processed in the whole chain of processes beginning with extraction and ending with disposal or recycling. The difference between the mass of the product itself and the total mass moved indirectly in the chain has been given the evocative term "rucksack." The size of the rucksack of a material product is a rough measure of the potential for disturbance resulting from its production and use.