Rethinking Due Diligence under the International Law of the Sea in an Era of Climate Change

Climate change is real. Climate change brings many trials to humanity, and small-island developing states and developing coastal States are the most affected by climate change, contrary to the concept of justice and the principle of proportionality in law. Under these circumstances, climate change vulnerable states are making various efforts to seek redress for their rights within the international legal system, including the law of the sea. In response to the question of how the law of the sea regime should respond to the challenges of climate change, this paper revisits the function and role of due diligence under the United Nations Convention on the Law of the Sea (“UNCLOS”). UNCLOS, often referred to as the Charter of the Sea, is a “living treaty” and an “open framework agreement” designed to adapt to changes, responding to the many challenges facing the oceans in our time. Thus, it is recognized that UNCLOS is capable of responding to climate change. In international law, the duty of due diligence serves as a “standard of conduct” to implement the primary norms, and the role of due diligence is becoming increasingly important in interpreting Part XII of UNCLOS for the protection of the environment at sea. In this regard, in its May 21, 2024 advisory opinion on climate change, ITLOS confirmed that the obligations undertaken by States under Articles 192 and 194 of UNCLOS are themselves a form of due diligence, and that due diligence is of a stringent nature. Furthermore, ITLOS has established that the standard of due diligence in Article 194(2), which addresses transboundary pollution, is more stringent than the standard of due diligence in Article 194(1). If this advisory opinion on the stringency of due diligence in determining whether States have fulfilled their obligations to protect the marine environment under Part XII of UNCLOS continues to be respected by States, and if the concept is developed in future international cases, it is possible that a precautionary approach and environmental impact assessment may be specifically required of States in the context of Part XII of the UNCLOS in the future.