The Evolution of Due Diligence Obligations in Climate Change Law: Insights from the Advisory Opinions of the International Tribunal for the Law of the Sea and the International Court of Justice, Implications for Vietnam

Abstract

Climate change is accelerating the development of international legal norms aimed at defining States’ responsibilities in preventing, mitigating, and responding to climate-related harms. In this context, the 2024 Advisory Opinion of the International Tribunal for the Law of the Sea (ITLOS) and the 2025 Advisory Opinion of the International Court of Justice (ICJ) represent significant milestones in clarifying the content of the due diligence obligation within international climate law. This article examines the theoretical foundations of due diligence and analyzes how this obligation has evolved through the legal reasoning and findings of ITLOS and the ICJ. It identifies emerging legal standards relating to the establishment of domestic climate governance frameworks, the regulation of greenhouse gas emissions, climate risk assessment and management, the supervision of private actors, and international cooperation. Building on this analysis, the article evaluates the compatibility of Vietnamese law with these emerging standards, highlights existing legal gaps, and proposes directions for legal reform. The article argues that due diligence is increasingly becoming a central normative principle of contemporary international climate law and that its domestic implementation is essential for strengthening Vietnam’s legal framework on climate change and enhancing the effectiveness of national climate governance.