In May 2024, the International Tribunal for the Law of the Sea (ITLOS) issued a landmark advisory opinion on climate change under international law. It unanimously determined that State Parties to the United Nations Convention on the Law of the Sea have specific obligations to take all necessary measures to prevent, reduce, and control marine pollution from anthropogenic greenhouse gas emissions. ITLOS noted that these obligations are ones of due diligence, and the standard of due diligence is “stringent,” given the high risks of serious and irreversible harm to the marine environment due to climate change; but it does not clarify what “stringent” due diligence means. This Comment provides an initial understanding of stringent due diligence by referencing the precautionary approach and the International Law Commission’s Draft Articles on Prevention of Transboundary Harm From Hazardous Activities.