1. Environmental indicators

Indicators are used in virtually all activities that involve decision making, although we may not be fully aware of it. The formal definition of indicator is: "Something that indicates, implies or signifies something through signs or signals. To point out, to warn, to express, to show." In other words, the key information we use to know something and, often, make a decision, is an indicator. Body temperature or blood pressure, for example, are indicators of our health condition and, according to their value, these allow us to make the decision to visit the doctor or not.

The ability to properly identify environmental indicators is essential to make better decisions; an incorrect choice of information or a poor understanding of the meaning of an indicator can lead to wrong interpretations and actions. It is therefore important to stress that an indicator is a tool, rather than an end in itself. Indicators are used in all areas of human activities, though these vary in the degree of complexity and relationship to the phenomenon they address, ranging from simple indicators, such as the color of a fruit that is used to assess its maturity, to more sophisticated ones, such as the concentration of immunological agents for detecting cancer.

Environmental indicators have been developed to understand, describe and analyze various phenomena such as climate, soil loss and species at risk, among many others. While the use of environmental indicators has been extended, there is no single definition of this concept and, consequently, it varies according to the institution and the specific objectives pursued. One of the best known and accepted definitions comes from the Organization for Economic Cooperation and Development (OECD), which since several years ago has used a set of indicators as basic information to conduct periodic assessments of the environmental performance of the organization’s member countries. According to the OECD, an environmental indicator is a parameter, or a value derived from parameters, that points to, provides information about and/or describes the state of the environment, and has a significance extending beyond that directly associated with any given parametric value.

For the Florida Center for Public Management, an institution that developed a system of indicators to provide advice to US environmental agencies, an environmental indicator is an element that describes, analyzes and displays scientifically supported information on environmental conditions and trends and their meaning (Florida Center for Public Management, 1998). Meanwhile, Canada’s Ministry of the Environment defines it as a statistic or parameter which, when monitored through time, provides information on trends or conditions of a phenomenon beyond those associated to the statistic itself. Particularly, it states that environmental indicators are selected key statistics that represent or summarize a significant aspect of the state of the environment, sustainability of natural resources and their relationships to human activities (Environment Canada, 1995).

To note, the words "parameter" and "index" are frequently used as synonyms of indicators; however, these have different meanings. A parameter is defined as any property that is either measured or observed, while an index refers to a set of aggregated or weighted parameters or indicators (OECD, 2001); further information on indices is provided below. 

1.1 Functions and characteristics of environmental indicators

The importance of indicators lies in the uses these serve for. Ideally, these should provide information to decision-makers or users, helping them to clarify a subject and unveil the relationships among their components, hence leading to improved decision making. They are also an excellent source of information for the public because, accompanied by a proper communication strategy, they illustrate scientific concepts and information, contributing to the understanding of issues and to a more active social participation in addressing environmental issues.

According to the OECD (1998), the two primary functions of environmental indicators are:

1. Reduce the number of measurements and parameters usually required to provide the closest possible view of the reality of a situation.

2. Simplify communication processes.

These core functions make indicators instruments through which concise and scientifically supported information is provided to different users, decision makers and the general public in a way that can be easily understood and used.

Environmental indicators have been used at international, national, regional, state and local levels for various purposes, including: to serve as tools for assessing the state of the environment, evaluate the performance of environmental policies and communicate progress made towards sustainable development. However, for indicators to fully meet these functions, they must fulfill a number of characteristics. A list of the most important characteristics is as follows (OECD, 1998):

1. Provide an overview of environmental conditions, environmental pressures and responses from the society or government.
2. Be simple, easy to interpret and able to show trends over time.
3. Respond to environmental changes and related human activities.
4. Provide a basis for international comparisons (as needed).
5. Be applicable at national or regional scales, as appropriate.
6. Preferably, include a reference value which they can be compared against.
7. Be theoretically and scientifically sound.
8. Be based on international consensus.
9. Able to be related to economic and/or development models and information systems.
10. Be available at a reasonable cost/benefit ratio.
11. Be well documented and have an acknowledged quality.
12. Be updated at regular intervals through reliable procedures.

Most indicators commonly used fail to meet all these characteristics. In this sense, it is important to consider that, to the extent that indicators fulfill fewer of the features listed above, their reliability will also decrease and, therefore, these should be interpreted with caution.

As a result of the experience in the development of indicators, the first three features are acknowledged as basic criteria. First, indicators should provide sufficient information on environmental conditions, environmental pressures and responses, to clearly understand the phenomenon of interest, so that any decisions made are properly supported. The value of indicators lies precisely on the assumption that a better understanding of a phenomenon or process leads to better decisions. It is worth remembering that one of the justifications for the use of indicators is that it is impossible to measure everything; hence, having the most relevant information is essential.

The second criterion is related to simplicity, which does not necessarily imply that the indicator is simplistic. The selection and definition of each indicator should be supported in a thorough and often complex analysis. However, when presented to users (decision-makers or society), the indicator must fulfill its primary mission of communicating its message clearly and objectively. This represents a challenge because there is always the tradeoff between incorporating technical details and the formality and rigor of analysis or removing them for easier interpretation (Adriaanse, 1993).

The third criterion, which focuses on responding to environmental changes and human activities, has been particularly useful in identifying indicators. Frequently, the analysis of an environmental phenomenon involves a number of important variables that are key for understanding its extent or distribution. However, when a negative answer is obtained to the question "Does this indicator respond to a possible change in policy?", then it is because context or supplementary information is being presented which, although crucial for understanding the phenomenon, is not an indicator. An example is the amount of rainfall when analyzing water availability in a region. The amount of rainfall in an area is essential to understanding the dynamics of the phenomenon and the establishment of policies and actions, but does not respond to any water management policy. In this respect, it is recommended that, along with indicators, additional background or supplementary information should be provided to facilitate a clearer understanding of what the indicator intends to describe.

The importance of conducting comparisons between countries was highlighted by the OECD. In this respect, it is essential that the methods for data collection and integration follow acknowledged, documented and –preferably- standardized procedures, so that any comparison of indicators (either with another country, state or region) is both possible and reliable. Another core aspect for the reliability or relevance of an indicator is the scale. For example, Mexico has information on soil loss at a 1: 1 000 000 scale, which is useful for understanding the situation at a country level. However, in most cases this resolution is not suitable for its use at a municipal level -although it is numerically feasible to make the calculations. In this sense, it is best that indicators be designed considering the intended scale of application (regional, state, national, international, etc.). In fact, it often happens that even the same subject requires specific indicators for each level.

It is essential to have a reference value that the indicator can be compared with, especially for users who measure the progress of specific policies and programs, since this allows a clearer assessment of performance. For example, having threshold pollutant values as a reference allows determining how close or far we are from achieving an acceptable condition. Unfortunately, in many cases there are no accepted reference values (World Bank, 1997). Examples of commonly used indicators that lack a defined and accepted threshold are: municipal waste generation, changes in land use, threatened species and water use intensity.

With regard to the remaining criteria, it is deemed essential that an indicator should be theoretically and scientifically sound, and that information should be available and updated regularly. All other criteria are considered just desirable.

Other agencies and organizations have also proposed criteria for assessing indicators. For example, the US National Academy of Sciences sets forth criteria that may be used to assess the potential importance of an indicator, its features, applicability and shortcomings. It suggests that these aspects be expressed as questions during the indicators’ selection and formulation process (National Academy of Sciences, 2003). To some extent, these criteria supplement the above list:

i) Overall Importance: Is the topic relevant? Does the indicator provide information on relevant changes or processes?
ii) Conceptual basis: Is the indicator based on an accepted and well-understood and scientifically sound conceptual model?
iii) Reliability: Has the indicator been useful in other indicators systems ?
iv) Spatial and temporal scales: Does the indicator have sufficient spatial or temporal resolution to assess changes or situations?
v) Statistical properties: Is the indicator sufficiently robust to differentiate between natural variability and fluctuations attributable to the measurement of the actual behavior of the phenomenon under study?
vi) Information requirements: Can the data required to document the indicator be obtained and are they reliable?
vii) Data quality: Is there clear information on how the information was obtained (e.g. calculation method, instrument used, etc.)? 

1.2. Indices and indicator sets

When a parameter or indicator is used to describe the situation of a subject, it often happens that it either fails to reflect properly the condition of the system or simplifies it, so that it is useless for decision making. For this reason, indices and "indicator sets" are often developed.

In complex issues, such as environmental ones, the development and use of indices is highly appealing because these provide an overview of the state of the environment.

Some of the best known indices that attempt to assess environmental sustainability are the Living Planet Index, the Ecological Footprint and the Environmental Sustainability Index (refer to the box Indices for assessing environmental sustainability).

The big challenge for indices is to convince that the assessments derived from them truly reflect the actual situation (i.e. environmental sustainability). The most frequent criticisms focus on three aspects: i) the criteria and rationale for selecting the subjects and variables included in the index, ii) the way in which these variables are integrated (i.e. the algorithms used), and iii) in the case of indices that seek to incorporate many subjects and make comparisons between countries (such as ESI), information heterogeneity and quality issues. Although it may seem paradoxical, as indices are designed to simplify complex systems, the correct interpretation of indices requires knowing both the way these were constructed and the criteria used for constructing them, as well as their shortcomings.

The OECD has classified currently existent indices into four groups: i) indices based on natural sciences, as the toxicity index, BOD or the global warming index); ii) indices for the evaluation of policies, which in general are related to regulatory aspects or policy targets; iii) indices based on a framework of national accounts, including "green accounts", the World Bank’s "true savings" index -where aggregation is achieved by assigning monetary values ​​to variables that generally are not priced- the "Ecological Footprint" (WWF, 2000) and "Total Materials Requirement" (WRI et al., 1997); and iv) synoptic indices, which ​​intend to provide a synthetic vision of a complex issue through a very small set of values, such as the Eurostat’s pressure indices, the Human Development Index and the Environmental Sustainability Index (OECD, 2001).

Another option for developing indices is to define sets of indicators which, when reviewed together, can provide a better and clearer assessment of the system. However, often the mistake is made of drawing conclusions from the results of a single indicator. For example, the observation of a drop in per-capita waste generation does not necessarily mean that we are making progress on environmental protection, since it could just result from a lower purchasing power derived from a lower income or even from higher unemployment rates. Another illustrative example is the magnitude of fish catches as an indicator of the health status of fish stocks of interest. The assumption that "healthy populations lead to greater catches" may lead to wrong conclusions, since it is possible that the increase in the amount of fish caught is due to an improvement in fishing methods; this misinterpretation may suggest that increasing the fishing effort is feasible, which would surely result in overexploiting the resource.

The sets of indicators for a particular system are determined by two different requirements:

1. Provide key information to gain a clear and complete picture about the current state of the system or phenomenon.
2. Provide sufficient information to make decisions to guide the system toward the goals chosen and determine the extent of success of actions implemented.

In other words, indices are determined both by the system itself as well as by the interests, needs and objectives pursued. This implies that the following is required: i) the broadest knowledge possible about the concepts and dynamics of environmental phenomena, and ii) clarity on the objectives, interests and needs to be achieved and monitored with the indicators (Bossel Hartmut, 1996).

While both aspects are essential for constructing an indicators system, in practice the latter is frequently either overlooked or minimized, leading to a chaotic and disorganized system unable to address a specific need. In other words, the selection and definition of the specific indicators to include in a given set depends on the objectives being pursued. In this respect, indicators that assess a country’s environmental policies may be substantially different from those needed to assess the sanitation policy of a basin or the effectiveness of an environmental management tool, since they not only differ in terms of scale and data aggregation but, additionally, variables that are relevant in one case may be meaningless in another. The usefulness of an indicator depends on the specific context; for example, the rate of soil loss may be essential for assessing environmental stability in mountainous land, but may be irrelevant, for example, in the tundra or permafrost permanently covered by ice.

In the case of environmental indicators, in addition to having information on the phenomenon, goals, interests and needs, it is necessary to fully understand the political needs; the key to a good set of indicators is finding a practical option for defining policies, implementing programs, issuing regulations, allocating budgets, etc. (World Bank, 1997). In this context, the first step in defining sets of indicators is to set priorities based on the institution’s environmental policies.

The usefulness of indicators is unquestionable, but it does not mean that they are perfect. At best, they reflect only part of reality; what we get from them is an abstraction of systems and of what we know about them. Notwithstanding these limitations, it must be acknowledged that indicators are probably the best decision-making tool available.

One way to advance the development of indices and indicator systems is to identify some of their common shortcomings:

• There is a risk of oversimplifying the issues and, thus, of misunderstanding the phenomenon. For example, the number of species is frequently used as an indicator of ecosystem health, under the assumption that a disturbed ecosystem loses species, but recently disturbed or mildly altered systems often show an increase in species numbers as a result of the invasion of exotic species.

• Aggregated indices may produce results which are too abstract to be easily understood. In this case, the rule is that a larger set of elements may not necessarily be a better indicator.

• A common problem in the process of identifying indicators is that these may reflect the particular experience of those who developed these as opposed to the needs of society. It is therefore highly recommended that these processes be participatory and incorporate the ideas and interests of both academic and government sectors and the civil society.

• With the emergence of new environmental issues or in view of a changing environment, it is important that indicators be flexible and can be reviewed periodically. If necessary, they should be amended, modified or replaced to better reflect the conditions and trends of the subject, and thereby remain useful. A good example of this need can be found in public health. One hundred years ago, the mortality associated with smallpox may have been a good indicator; today it is not. Similarly, if in those years deaths from HIV or obesity-related diseases had been used as health indicators, they would surely have had very little use, but nowadays these are highly relevant.

Unfortunately, nowadays there is a growing trend towards having indicator systems in place, even without clear objectives associated with them, so there is a higher risk that these efforts be of little use. Needless to stress, for an indicator system to truly perform its function, it should be associated with an information system that ensures the availability of data for updating the indicators and a team in place that regularly reviews, updates or modifies indicators in order to maintain their usefulness. The National System of Environmental Indicators developed by the SEMARNAT is associated with the National System of Environmental Information and Natural Resources (SNIARN, for its acronym in Spanish) as well as with integrative products such as the State of the Environment Report .