Although uncertainties about the consequences of human behaviour have always existed, they have become more significant in recent times because of the growing scope, complexity and hazardous consequences of human activities.

This means it is becoming ever more vital to prevent the harm these activities might do, even without being sure what that harm might be.

While modern environmental regulations are anticipatory and pre­ventive they are not necessarily precautionary.

Risk 'is usually defined as the amalgam of the probability of an event occurring and the seriousness of the consequences should it occur' (Cameron 1999: 37). For example, the risk of a major nuclear power acci­dent is the combination of a low probability of such an accident, which engineers claim can be calculated, multiplied by the serious damage that would occur as a result of the spread of nuclear radiation, including thousands of deaths, cancers, birth defects. If the risk of an accident is considered too high then a nuclear power plant will not be granted approval and thus the risk is prevented.

If one accepts that the risk of a nuclear accident can be calculated with some degree of accuracy, the precautionary principle does not apply. If, however, one believes that engineers are unable to calculate the probability of a major nuclear accident with any reasonable certainty or accuracy, then the precautionary principle does apply.

If an activity or product poses a known high risk then preventive action is called for rather than precautionary action. It is only when the risk is uncertain because either the probability of damage is uncertain and/or the extent of damage is uncertain that the precautionary principle applies.

Box 3.1 Definition of the precautionary principle

When human activities may lead to morally unacceptable harm that is scientifically plausible but uncertain, actions shall be taken to avoid or diminish that harm.

Morally unacceptable harm refers to harm to humans or the environ­ment that is

• threatening to human life or health, or

• serious and effectively irreversible, or

• inequitable to present or future generations, or

• imposed without adequate consideration of the human rights of those affected.

The judgment of plausibility should be grounded in scientific analysis. Analysis should be ongoing so that chosen actions are subject to review.

Uncertainty may apply to, but need not be limited to, causality or the bounds of the possible harm.

Actions are interventions that are undertaken before harm occurs that seek to avoid or diminish the harm. Actions should be chosen that are proportional to the seriousness of the potential harm, with consideration of their positive and negative consequences, and with an assessment of the moral implications of both action and inaction. The choice of action should be the result of a participatory process.

Source (COMEST 2005: 14)