Approach/principle according to which the absence of full scientific certainty shall not be used as a reason for postponing action where there is a risk of serious or irreversible harm to the environment or human health. The approach/principle is embedded in several instruments, including Principle 15 of the 1992 Rio Declaration on Environment and Development. Whereby the precautionary approach is often used in negotiations to infer a less definite meaning than the precautionary principle.