환경손상 방지의무와 사전주의 원칙의 교차: 실체적 의무와 절차적 의무 간의 접점을 중심으로

This paper examines the interaction between the obligation to prevent environmental harm and the precautionary principle, which together form the core framework of international environmental law amid the climate crisis marked by scientific uncertainty. The obligation to prevent has evolved from the no-harm rule and has been further articulated through due diligence and procedural duties such as environmental impact assessment (EIA), prior notification, and consultation. The precautionary principle, originating in German environmental law in the 1980s, has since developed into a central principle of international environmental law. Debates over its legal status, scope, and conditions of application reveal intersections with the obligation to prevent, highlighting both commonalities and differences—notably regarding reasonableness versus plausibility, the allocation of the burden of proof, and its relationship to shared resources and the global commons. When combined with the obligation to prevent, the precautionary principle requires States to take prompt preventive measures even amid scientific uncertainty, potentially shifting the responsibility framework toward a risk-sharing model resembling a strict liability regime. In this sense, the precautionary principle functions not merely as a policy guideline but as a standard capable of translating uncertainty into a breach of due diligence obligations. However, because the obligation to prevent requires ordinary due diligence while the precautionary principle demands a heightened standard of care, it is crucial to delineate their respective scope and function; otherwise, the flexibility of due diligence risks being conflated with the indeterminacy of precaution. Recent jurisprudence of the ICJ and ITLOS has clarified this relationship by placing precaution, alongside risk assessment, EIA, and notification and consultation, within the elements of due diligence—thus reinforcing procedural duties while anticipating substantive measures. In particular, the precautionary principle operates as a “trigger” for procedural duties under conditions of uncertainty and as a substantive benchmark preventing delay in preventive action. It thereby functions as a cross-cutting principle restructuring the obligation to prevent environmental harm. Nevertheless, the coexistence of different risk thresholds—such as significant harm and serious or irreversible harm—continues to generate uncertainty across both substantive and procedural obligations. Moreover, while the ICJ has rejected presumptions in causation, it has placed an onerous burden of proof on non-party States in relation to the duty to cooperate, leaving open questions about the consistency between strict attribution of harm and the effectiveness of cooperation. In conclusion, the precautionary principle simultaneously strengthens substantive measures and activates procedural duties, shaping new standards of conduct under the customary obligation to prevent environmental harm. Yet this development raises challenges for legal stability and predictability, underscoring the need for further clarification of its scope and operational criteria, particularly in multilateral contexts such as climate change.