Humanity's conceptualization of the global environment has changed radically in the four decades since the publication of Rachel Carson's Silent Spring. In many respects, there has been a fundamental transformation within the sciences, social sciences and humanities with the emergence of such critical disciplines as ecology, environmental ethics and, more recently, ecological economics. Underlying this remarkable disciplinary change has been a dramatic paradigm shift--from humanity as dominant over, yet independent of, the natural environment, to humanity as one, albeit important, element of a complex interrelated array of ecological entities. This reformulation of humanity's place in the global ecosystem crystallized in 1987 with the publication of the Bruntland Report and the articulation of the concept of sustainable development.
Defined simply as "development which meets the needs of the present without compromising the ability of future generations to meet their own needs," the concept of sustainable development has spurred a vast interpretative research literature which has focussed on its implications across a broad range of human activities and academic disciplines. Beguilingly simple in its phraseology, sustainable development has created an extraordinary intellectual challenge--first, to define it operationally and, second, to generate metrics to assess change both toward and away from it.
At the heart of sustainable development is the concept of systems theory--that all elements of a system are interrelated and that the whole is greater than the sum of its parts. In simplest terms, sustainable development encompasses three subsystems. It is based on the analogy of a three-legged stool, requiring the simultaneous achievement of sustainability in three disparate spheres: economic, ecological and social. In the last category, sustainable development must address both intragenerational and intergenerational equity; i.e. issues of empowerment and distributional equity not only among the current inhabitants of the earth, but also across generations yet to be born. Several critical conceptual threads run throughout studies of sustainability:
(1) a distinction between qualitative and quantitative changes in the utilization of our technology and natural resource base (i.e. development versus growth). Central to operationalizing this distinction are technological advances which may permit us to raise our standard of living without increasing the throughput of resources--a process commonly referred to as "dematerialization;
(2) a focus on social justice, stability and empowerment with particular emphasis on reducing poverty and maintaining an adequate quality of life for all global inhabitants;
(3) borrowing from principles of business sector accounting, a direct or indirect articulation of the concept of natural capital--where maintenance of a constant natural capital stock (including the renewable resource base and the environment) yields an indefinite stream of output or "income." At its core is the proposition that the current generation must leave its descendents a stock of capital no less than is currently available. Implicit in this proposition is that we must, to the best of our ability, live off the "interest" on this capital stock and not draw it down. If part of this capital is consumed, it must be replaced by substitute capital. The ability to achieve this goal hinges on which of two alternative definitions is adopted: "weak" sustainability or "strong" sustainability.
Under the weak sustainability constant capital rule, we can consume some of our natural capital (in the form of environmental degradation, for example) as long as we offset this loss by increasing our stock of man-made capital. In contrast, under the strong sustainability constant capital rule, there is no perfect substitution among different forms of capital. …