EIS (environmental impact statement)

Societies are attempting to develop means of coping with the environmental stressors caused by human activities. These include the activities of individual people as they go about their daily lives, as well as the larger enterprises of corporations, governments, and society at large. One of the procedures that is increasingly becoming a routine component of planning for potential damages is known as environmental impact assessment.

The environmental impact assessment (EIA), and the subsequently prepared statement (EIS), is a process that can be used to identify and estimate the potential environmental consequences of proposed developments and policies. Environmental impact assessment is a highly interdisciplinary process, involving inputs from many fields in the sciences and social sciences. Environmental impact assessments commonly examine ecological, physical/chemical, sociological, economic, and other environmental effects.

Environmental assessments may be conducted to review the potential effects of: (1) individual projects, such as the construction of a particular power plant, incinerator, airport, or housing development; (2) integrated development schemes, or proposals to develop numerous projects in some area . Examples include an industrial park, or an integrated venture to harvest, manage, and process a natural resource, such as a pulp mill with its associated wood-supply and forest-management plans; or (3) government policies that carry a risk of having substantial environmental effects. Examples include decisions to give national priority to the generation of electricity using nuclear reactors, or to clear large areas of natural forest to develop new lands for agricultural use.

An extraordinary variety of environmental and ecological changes can potentially be caused by any project, scheme, or policy. Consequently, it is never practical in an environmental impact assessment to consider all of the potential effects of a proposal. Usually certain indicators, called "valued ecosystem components" (VECs), are carefully selected for study, on the basis of their importance to society. The valued ecosystem components are often identified through consultations with representatives of regulatory agencies, scientists, non-governmental organizations, and the public.

Examples of commonly examined VECs include: (1) resources that are economically important, such as agricultural or forest productivity, and populations of hunted fish or game;(2) rare or endangered species and natural ecosystems; (3) particular species, communities, or landscapes that are of cultural or aesthetic importance; and (4) simple indicators of a complex of ecological values. The spotted owl, for example, is an indicator of the integrity of certain types of old-growth conifer forests in western North America . Any proposed activity, likely associated with forestry, that threatens a population of these birds also indicates a challenge to the larger, old-growth forest ecosystem.

The initial phase of an environmental impact assessment attempts to screen for potentially important conflicts between proposed activities and valued ecosystem components. Essentially, this is done by predicting the dimensions in space and time of stressors associated with the proposed development, and then comparing these with the known boundaries of VECs. This is a preliminary, scoping exercise, which may require environmental scientists to make professional judgments about the severity and importance of potential interactions between stressors and VECs. The best-available information is used to guide these interpretations, although the existing knowledge is almost always incomplete. To better determine the risks of interactions identified during the preliminary screening, it is highly desirable to undertake field, laboratory, or simulation research. However, time and funds are not always available to support new research, and this can constrain some impact assessments.

Once potentially important risks to VECs are identified and studied, it is possible to consider various planning options. During this stage of the impact assessment, environmental specialists provide objective information and their professional opinions to decision makers, who must then make choices that deal with the conflicts. There are three broad types of choices that can be made:

(1) The predicted damages can be avoided, by not proceeding with the development, or by modifying its structure. However, avoidance is often considered an undesirable option by proponents of a development. This is because irreconcilable conflicts with environmental quality can result in substantial costs, including canceled projects. Regulators and politicians also tend to resent this option, because socioeconomic opportunities can be lost, and there is often intense controversy.

(2) Often, mitigations can be designed and implemented to prevent or significantly reduce damages to the VEC. For example: (a) if an industrial activity is predicted to acidify a lake, an appropriate mitigation might be liming to reduce the acidification; (b) if habitat of an endangered species is threatened, the risk may be mitigated by moving the population to another site; or (c) the emissions of carbon dioxide from a proposed coal-fired generating station could be offset by planting trees to achieve no net change in atmospheric concentrations of this gas. Mitigations are common ways of resolving conflicts between project-related stressors and VECs. However, there are always substantial risks with the use of mitigations, because ecological and environmental knowledge are incomplete, and it is not necessarily known if mitigations will actually work properly to protect the VEC.

(3) Another option that is often selected is to allow the damages to the VEC to occur, and to accept the degradation as an unfortunate cost of achieving the perceived socioeconomic benefits of proceeding with the development. This choice is common, because not all environmental damages can be avoided or mitigated, and many damaging activities can yield large, short-term profits.

It is not possible to carry out large industrial or economic developments without causing some environmental damages. However, a properly done impact assessment can help decision makers to understand the dimensions and importance of those damages, and to decide whether they are acceptable, or whether they must be reduced or avoided.

See also Earth (planet); Earth science