Sustainable development indicators (SDI) are measures of sustainability, and attempt to quantify beyond the generic concept. Though there are disagreements among those from different disciplines (and influenced by different political beliefs about the nature of the good society), these disciplines and international organizations have each offered measures or indicators of how to measure the concept.
While sustainability indicators, indices and reporting systems gained growing popularity in both the public and private sectors, their effectiveness in influencing actual policy and practices often remains limited.
University of Maryland School of Public Policy professor and former Chief Economist for the World Bank Herman E. Daly (working from theory initially developed by Romanian economist Nicholas Georgescu-Roegen and laid out in his 1971 opus “The Entropy Law and the Economic Process”) suggests the following three operational rules defining the condition of ecological (thermodynamic) sustainability:
- Renewable resources such as fish, soil, and groundwater must be used no faster than the rate at which they regenerate.
- Nonrenewable resources such as minerals and fossil fuels must be used no faster than renewable substitutes for them can be put into place.
- Pollution and wastes must be emitted no faster than natural systems can absorb them, recycle them, or render them harmless.
Some commentators have argued that the “Daly Rules”, being based on ecological theory and the Laws of Thermodynamics, should perhaps be considered implicit or foundational for the many other systems that are advocated, and are thus the most straightforward system for operationalization of the Bruntland Definition. In this view, the Bruntland Definition and the Daly Rules can be seen as complementary—Bruntland provides the ethical goal of non-depletion of natural capital, Daly details parsimoniously how this ethic is operationalized in physical terms. The system is rationally complete, and in agreement with physical laws. Other definitions may thus be superfluous, or mere glosses on the immutable thermodynamic reality.
There are numerous other definitions and systems of operationalization for sustainability, and there has been competition for influence between them, with the unfortunate result that, in the minds of some observers at least, sustainability has no agreed-upon definition.