Coastal landowners have an acute interest in armoring the shoreline by erecting barriers to protect their property from inundation and erosion. One problem with armoring is that the barrier potentially destroys coastal wetlands and beaches and prevents them from migrating as sea levels rise. Under the public trust doctrine, the public has the right to use trust resources and, in some states, to conservation of trust resources and the ecological services they provide. This Article examines whether coastal states have authority to take preemptive action to adapt to sea-level rise and protect intertidal zones, and whether they also have an enforceable duty under the public trust doctrine to take preemptive action. It concludes that, given the magnitude of the problems presented by global climate change and sea-level rise, the doctrine demands that states take action to protect trust resources.