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.