If we choose not to act to ameliorate a risk that later proves valid, we have made a false negative error and forfeit simpler, more parsimonious, and less wrenching solutions to risks by failing to act in a timely fashion. If response time is even longer, expensive remediation may be necessary or resources may be lost for which there is no possible replacement, including, but not limited to, human life. As the systems whose future is being predicted become larger and more complex, the errors grow more costly. Both science and ethics have roles in environmental decision making. In most risk assessment schemes, science and ethics come into play sequentially.
Ethical considerations define what society considers as a problem requiring action.
Science contributes probablistic statements about the nature of the world, the connections between events, and probabilities of future happenings, but science does not tell us what we should do. Ethics or societal consensus comes into play again in the risk management phase as the relative importance of uncertainties, risks, and benefits is weighed and a course of action is chosen. The decision maker can make an educated guess about the future, but must weigh the uncertainty of the prediction against the unpleasant consequences should the decision be wrong. The uncertainty of an estimate of risk can be of little importance if a decision is made to avoid the risk because the magnitude of harm is large but the resulting magnitude of benefits is small. In addition, a large probability of a small adverse effect in combination with widespread and large benefits might be judged acceptable.