Rising sea levels in the wake of climate change has the potential to undermine existing legal regimes that govern control of the world’s oceans and continental shelves. Climate-driven environmental changes are already destabilizing the Arctic and fostering new types of alliances. By altering commonly accepted baselines that are used to determine the right of states to extend state control outward from their shores, they also have the potential to undermine fragile accords in the maritime arena, and to create new sources of instability. From a policy perspective, recognizing that rising sea levels will likely undermine existing maritime regimes points to the need for proactive agreements that anticipate changes in the configuration of coastlines. Conceptually, the potential for environmental change to alter jurisdictional arrangements highlights the importance of challenging the long-standing tendency to treat the environment as a constant in geopolitical analyses.