A Guidebook to Environmental Indicators

Identifying potential indicators, and selecting the best to provide focused information for policy makers and managers, depends on several sorts of criteria. They can be grouped into those associated with human activities and impacts; the needs of society, policy makers and managers; and the scientific understanding needed. These are taken up in accompanying sections.

Good indicators generally rest on understanding the links between a human activity and its consequences. Sometimes indicators are associated with incomplete understanding: these should be used with care and efforts made to understand the linkages fully. The link between clearing native vegetation and negative effects on biodiversity, or the observation that exhaust from cars degrades air quality in major cities, are examples where there is scientific consensus about the relationships.

Where causal links between activities and effects are well understood, it may be possible to use indicators as early warning signals: stratospheric ozone depletion illustrates this. It will often be helpful to choose indicators with relationships to human activities since these are better understood and easier to measure, and alter, than many non-human processes. Unsurprisingly, the values helping guide indicator choice often reflect human-centred concerns such as health impacts.

Ozone depletion
Mario Molina and Sherwood Rowland warned in 1974 that man-made gases such as chlorofluorocarbons (CFCs) could damage the stratospheric ozone layer that screens out much of the sun's harmful UV radiation. Unfortunately, little attention was paid to this warning (except in the United States) until the mid 1980s, when a 'hole' was discovered in the stratospheric ozone layer above the Antarctic. This hole has since captured attention as an indicator of the state of the world's ozone layer.

This problem was addressed by phasing out production and use of CFCs and other ozone depleting substances. Because of natural variations and the time for existing CFCs to decompose, it is too early to confirm improvement in the ozone layer. However, declining production of ozone depleting substances and their concentrations in the atmosphere are excellent indicators of progress.

While some human activities harm the environment, others are beneficial. Indicators often draw attention to harmful activities, but it is important to avoid the mindset that most human activities are negative. There are also useful indicators of natural factors which impact on human activities.

Indicator performance can vary depending on whether human impacts are acute or chronic, local or regional, and limited or cumulative in effect. Many activities, such as fishing, agriculture, and driving cars, have a continual effect on the environment. Others may fluctuate strongly: major shipping accidents, for example, can powerfully affect the environment, but are sporadic. The nature of the activities and impacts should be assessed as part of choosing indicators.