to argue that some categories of natural capital should be defined as critical and thus not be allowed to fall below a minimum level: (1) a reasonably stable and predictable climate; (2) air that is safe to breath; (3) high-quality water in sufficient quantities; and (4) intact natural landscapes suitable for supporting a diversity of plant and animal life (UN/EC/IMF/OECD/World Bank 2003). Taking into account the difficulty of developing monetary measures for all the concepts needed, the authors argue for the use of physical measures and other proxies in developing a practical indicator set.
The authors noted that in actual practice, most sustainable-development indicator sets were policy-based—that is, capable of changing over a sufficiently short period of time to attribute the changes at least in part to specific policy measures. Examples of these types of indicators are emissions of greenhouse gases on an annual basis, energy use per unit of gross domestic product (GDP), mortality due to selected key illnesses. They identify 27 indicators used in indicator sets by at least 10 countries (see Table E-1). The authors do not question the usefulness of the policy-based approach, but strongly advocate that it be complemented by outcome-based indicators using the capital stocks- and flow-approach (UN/EC/IMF/OECD/World Bank 2003). Examples of these types of indicators are (1) (stock) average annual concentrations of ground level ozone, (flow) smog-forming pollutant emissions per month; (2) (stock) health-adjusted life expectancy, (flow) annual changes in age-specific mortality and morbidity, (3) (stock) real per capita natural capital, (flow) real per capita net depletion of natural capital. For more examples, see Table E-2.
The authors also reported a comparison of national and international sustainable-development strategies where they found that 11 indicator themes were common to a large number of the strategies: management of natural resources, climate change and energy, sustainable consumption and production, public health, social inclusion, education, socioeconomic development, transportation, good governance, global dimension of sustainable development, research and development, and innovation (UN/EC/IMF/OECD/World Bank 2003). The authors of the report suggested that most of the strategies can be captured by the outcome-based indicators they propose but that indicators related to efficiency and equity might well be added to the set to capture other dimensions of policy.
While the work mentioned above was under way, the United Nations Commission for Sustainable Development (UNCSD) revised its set of indicators in Indicators of Sustainable Development: Guidelines and Methodologies (UNCSD 2007). Because many of the same statisticians contributed to both exercises, there is considerable overlap, at least among the policy-based indicators. The UNCSD set now contains 50 core indicators among a larger set of 96 sustainable-development indicators. Among the 27 indicators mentioned above, all but one (unemployment rate) are included in the broader UNCSD set, and 20 of them are included among the core set.