Because decoupling indicators relate environmental pressures to socioeconomic driving forces, their evolution over time must be evaluated against the absolute levels of environmental pressure or state variables. For many of these it is necessary to have explicit policy targets. For pollution pressures, most OECD countries have set both environmental quality standards (e.g., receiving water and ambient air quality standards) and effluent or emission limits. These targets are generally based on a scientific assessment of environmental quality objectives and associated levels of maximum environmental pressure. Some countries also apply benefit—cost analysis to ensure that the costs to society of ensuring compliance with the limits do not exceed the benefits of doing so. A number of countries also use other evaluation tools such as strategic environmental assessments or sustainability impact assessments. At the regional and international levels, there are several legally binding conventions and agreements setting targets (emission ceilings) for particular environmental pressures (e.g., sulfur dioxide, volatile organic substances).
For natural resources, uses can be viewed either as a driving force (expressed in value terms) or as a pressure on the environment (measured in physical units). For example, the use of nonrenewable resources (e.g., fossil fuels) is often treated as a driving force when the environmental variable of interest is a pollutant. Regarding renewable resources (e.g., water, fish, wood), their use is considered mostly a pressure changing in response to an economic driver, such as household consumption. For some resources, many countries have imposed constraints on natural resource use because of the environmental pressure they generate. For example, the abstraction of surface water sometimes is regulated in order to maintain adequate flows in rivers for the protection of aquatic ecosystems. However, these targets are less well developed than those for pollution pressures.
Pressure reduction targets at a national or international level have so far been expressed in absolute (e.g., tons of sulfur dioxide per annum) rather than relative terms (emissions per unit of GDP or resource use per unit of GDP). However, in some cases only relative decoupling targets may be politically feasible even where the long-term objective may be a reduction in the absolute levels of environmental pressure.6 Applied to products, decoupling targets, usually called performance standards, are increasingly used (e.g., minimum energy performance standards for electrical appliances). Where possible, trends in decoupling can be compared with policy targets to show the "distance to target." However, even in the absence of defined thresholds, ceilings, or targets, decoupling indicators are useful to compare countries, to identify similarities and differences, and as a starting point to assess the potential for improved performance. They are particularly well suited for assessing the adequacy of the policy measures implemented to achieve decoupling.
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