The Difficulty in Defining Sustainability

“Sustainability" has become a new watchword by which individuals, organizations, and nations are to assess human impacts on the natural environment and resource base. A concern that economic development, exploitation of natural resources, and infringement on environmental resources are not sustainable is expressed more and more frequently in analytical studies, conferences, and policy debates. This concern is a central theme in the international deliberations leading up to the United Nations Conference on Environment and Development. To identify what may be required to achieve sustainability, it is necessary to have a clear understanding of what sustainability means.

Like many evocative terms, the word sustainability (or the phrase "sustainable development," which more strongly connotes concerns of particular importance to developing countries) means many things to different people and can be used in reference to a number of important issues. The term inherently evokes a concept of preservation and nurturing over time. The World Commission on Environment and Development (known popularly as the Brundtland Commission) labeled sustainable development in its 1987 report Our Common Future as "development that meets the needs of the present without compromising the ability of future generations to meet their own needs." Thus sustainability involves some notion of respect for the interests of our descendants. Beyond this point, however, uncertainty and disagreement are rife.

In scholarly usage, the term sustainability originally referred to a harvesting regimen for specific reproducible natural resources that could be maintained over time (for example, sustained-yield fishing). That meaning has been considerably broadened by ecologists in order to express concerns about preserving the status and function of entire ecological systems (the Chesapeake Bay, the biosphere as a whole). Economists, on the other hand, usually have emphasized the maintenance and improvement of human living standards, in which natural resources and the environment may be important but represent only part of the story. And other disciplines (notably geography and anthropology) bring in concerns about the condition of social and cultural systems (for example, preservation of aboriginal knowledge and skills).

Beyond ambiguity of meaning there also is disagreement about the prospects for achieving sustainability. The Brundtland Report foresees "the possibility for a new era of economic growth, one that must be based on policies that sustain and expand the environmental resource base." Some scholars, notably the economist Julian Simon, question whether sustainability is a significant issue, pointing out that humankind consistently has managed in the past to avoid the specter of Malthusian scarcity through resource substitution and technical ingenuity. Others, notably the ecologists Paul and Anne Ehrlich and the economist Herman Daly, believe that the scale of human pressure on natural systems already is well past a sustainable level. They point out that the world's human population likely will at least double before stabilizing, and that to achieve any semblance of a decent living standard for the majority of people the current level of world economic activity must grow, perhaps fivefold to tenfold. They cannot conceive of already stressed ecological systems tolerating the intense flows of materials use and waste discharge that presumably would be required to accomplish this growth.

Ascertaining more clearly where the facts lie in this debate and determining appropriate response strategies are difficult problems—perhaps among the most difficult faced by all who are concerned with human advance and sound natural resource management. Progress on these fronts is hampered by continued disagreements about basic concepts and terms of reference. To narrow the gaps, it may be helpful first to identify salient elements of the sustainability concept about which there are contrasts in view between economists and resource planners on the one hand, and ecologists and environmental ethicists on the other.

Key conceptual issues

As noted above, intergenerational fairness is a key component of sustainability. The standard approach to intergenerational tradeoffs in economics involves assigning benefits and costs according to some representative set of individual preferences, and discounting costs and benefits accruing to future generations just as future receipts and burdens experienced by members of the current generation are discounted. The justifications for discounting over time are first, that people prefer current benefits over future benefits (and weight current costs more heavily than future costs); and second, that receipts in the future are less valuable than current receipts from the standpoint of the current decision maker, because current receipts can be invested to increase capital and future income.

Concerns over intergenerational fairness, resource constraints, and human scale provide a rationale for some form of intergenerational social contract (though such a device can function only as a 'thought experiment" for developing our own moral precepts, since members of future and preceding generations cannot actually be parties to a contract). One way to give shape to such a contract is to apply the concept of a safe minimum standard, an idea that has been advanced (sometimes with another nomenclature) by a number of economists, ecologists, philosophers, and other scholars.

To simplify somewhat, suppose that damages to some natural system or systems can be entirely characterized by the size of their cost and degree of irreversibility. Since ecologists do not view all the effects of irreversibility as readily monetizable, these two attributes of damages are treated separately (see figure, p. 5). The magnitude of cost can be interpreted in terms of opportunity cost by economists or as a physical measure of ecosystem performance by ecologists.

Irreversibility reflects uncertainty about system performance and the resulting human consequences. At one extreme, very large and irreversible effects may threaten the function of an entire ecosystem. At a global level, the threat could be to the cultural if not the physical survival of the human species. In the figure, this extreme is represented at the upper lefthand corner. At the other extreme (the lower righthand corner), small and readily reversible effects are relatively easily mediated by private market transactions or by corrective government policies based on comparisons of benefits and costs.

There is uncertainty about how rapidly the threat to current and future human welfare grows as damages become costlier and irreversibility becomes more likely. The safe minimum standard posits a socially determined dividing line between moral imperatives to preserve and enhance natural resource systems and the free play of resource tradeoffs. To satisfy the intergenerational social contract, the current generation would rule out in advance actions that could result in natural impacts beyond a certain threshold of cost and irreversibility. Rather than depending on a comparison of expected benefits and costs from increased pressure on the natural system, such proscriptions would reflect society's value judgment that the cost of risking these impacts is too large. Possible resources for which society would not risk damages beyond a certain cost and degree of irreversibility include wetlands, other sources of genetic diversity, the climate, wilderness areas, Antarctica, and other ecosystems with unique functional or aesthetic values (like the Grand Canyon).

There is a distinct difference between the safe minimum standard approach and the standard prescriptions of environmental economics, which involve obtaining accurate valuations of resources in benefit-cost assessments and using economic incentives to achieve efficient resource allocation given these valuations. Whether a resource-protection criterion is established by imperatives through an application of the safe minimum standard concept or by tradeoffs through cost-benefit analyses, that criterion can be cost-effectively achieved by using economic incentives. However, for impacts on the natural environment that are uncertain but may be large and irreversible, the safe minimum standard posits an alternative to comparisons of economic benefits and costs for developing resource-protection criteria. It places greater emphasis on potential damages to the natural system than on the sacrifices experienced from curbing ecological impacts. The latter are seen as likely to be smaller and more readily reversible. In addition, the safe minimum standard invokes a wider, possibly less individualistic set of values in assessing impacts. Since societal value judgments determine the level of safeguards, public decision making and the formation of social values are explicit parts of the safe minimum standard approach.

There is a need for much additional interdisciplinary work to refine the concept of sustainability. Along with basic concept definitions, extensions of economic and ecological theory to more fully account for the objectives and constraints of sustainability would be useful. To clarify some of the points of disagreement already outlined, substantial interdisciplinary data-gathering and analysis also would be required. This empirical work should address issues in developing countries and in developed countries, and those relevant to the entire world.

The tension between ecological and economic perspectives on sustainability suggests several ways in which both economists and ecologists could adapt their research emphases and methodologies to make the best use of interdisciplinary contributions. Economists could usefully expand analyses of resource values to consider the function and value of ecological systems as a whole, making greater use of ecological information in the process. Economic theory and practice also could be extended to consider more fully the implications of physical resource limits that often are not reflected in more stylized economic constructs. In addition, research by economists and other social scientists (psychologists and anthropologists) could help to improve understanding of how future generations might value different attributes of natural environments. Finally, the sustainability debate should remind economists to carefully distinguish between efficient allocations of resources—the standard focus of economic theory—and socially optimal allocations, which may include intergenerational (as well as intragenerational) equity concerns.

For ecologists, the challenges include providing information on ecological conditions in a form that could be used in economic valuation. Ecologists also must recognize the importance of human behavior, particularly behavior in response to economic incentives—a factor often given short shrift in ecological impact analyses. Finally, it must be recognized that human behavior and social decision processes are complex, just as ecological processes are. What may appear as self-evident to the student of natural environment need not seem so for the student of human society, and vice versa.