Sustainability - an evolving framework

What is meant by sustainability?

For any given technology, preference structure, and known resource base there are some utilization rates that cannot be sustained. Drawing attention to these unsustainable rates is critical to informing decisionmakers and changing course toward sustainability. This will often require altering the pattern of preferences, the resource intensity of technologies, or the relevant time horizon for different decisions. Since none of these is constant or stable over time, defining sustainability in a broader sense is not easy-but there have been many attempts. The most commonly used definition is the one provided by the World Commission on Environment and Development (Brundtland Commission 1987): "progress that meets the needs of the present without compromising the ability of future generations to meet their own needs."

While the Brundtland definition highlights the need to balance the interests of current and future generations, it does not define the concept of needs or its implications. For instance, does the Brundtland definition imply that well-being (utility) should not fall below some minimum for any subsequent generation? Does it imply that each generation should enjoy a constant level of well-being? Alternatively, should well-being be nondeclining for each future generation? Most later definitions have retained the core ethic of intergenerational equity, emphasizing the current generation's moral obligation to ensure that future generations enjoy at least as good a quality of life as the current generation has now (Pezzey 1989).

Recent definitions have focused more explicitly on the three pillars of sustainability: economic, environmental, and social. These highlight the need to consider not only the environmental, or even the environmental and economic aspects, but also the social aspects of sustainability. The thinking about social sustainability is not yet as advanced as for the other two pillars. Societies do, and will continue to, transform over time. But it seems clear that significant social stress -and, at the extreme, social conflict- is likely to lead to a breakdown in the accumulation or preservation of all assets, thereby jeopardizing intergenerational well-being.

One concrete approach to thinking about sustainability and intergenerational well-being is to ensure that the flow of consumption does not decline over time. But what is needed for this? The academic literature shows that a country's ability to sustain a flow of consumption (and utility) depends on the change in its stock of assets or wealth. Intergenerational well-being will rise only if wealth (measured in shadow prices and excluding capital gains) increases over time-that is, only if a country's adjusted net savings are positive.^{3, 4} (See the section titled "Measuring sustainability.")