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Keywords

climate change; customary international law; international environmental law; international climate law; climate obligations; International Court of Justice; ICJ advisory opinion; obligations of states in respect of climate change; state responsibility; state practice; opinio juris; persistent objector doctrine; duty to prevent significant environmental harm; duty to cooperate; transboundary environmental harm; due diligence; environmental protection; climate litigation; United States; domestic application of international law; federal common law; climate regulation; greenhouse gas emissions; Paris Agreement; United Nations Framework Convention on Climate Change; UNFCCC; Clean Air Act; Environmental Protection Agency; endangerment finding; climate deregulation; President Donald Trump; Lee Zeldin; Trump administration; climate policy rollbacks; EPA deregulation; National Oceanic and Atmospheric Administration; NOAA; climate science; climate research; climate data; National Climate Assessment; U.S. Global Change Research Program

Abstract

On July 23, 2025, the International Court of Justice (ICJ) issued its “Advisory Opinion on Obligations of States in Respect of Climate Change,” concluding that “the full gamut of international law applies to climate change.” Beyond treaty-based duties, the ICJ recognized that customary international law imposes obligations on all states to protect the climate. The advisory opinion emerged from unprecedented participation by states and international organizations, reflecting a growing consensus that addressing climate change is a legal obligation. This Note explores the legal implications of recognizing a customary international law duty to protect the climate system. It posits that these customary obligations bind the United States as a matter of both international and domestic law. Therefore, recent regulatory and scientific rollbacks under President Donald J. Trump’s administration place the United States in breach of its duties to prevent significant environmental harm and to cooperate in good faith with other states.

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