The rising politics of sea level: demarcating territory in a vertically relative world

Sea level rise has destructive material impacts on coastal communities and low-lying nations. While it is largely perceived and experienced via these impacts, the level of the sea is less often thought about as a political surface. The boundary where land and sea intersect is determined by the ocean’s height, manifesting materially as a realm of coastal features and produced politically as baselines. Defined through international treaties, baselines are the low-water line upon which national boundaries are traced. Yet, this line between adjoining mediums of land and sea is much more physically blurred and dynamic than represented politically and legally. The difficulties of delimiting a coastline, a phenomenon referred to as the Coastline Paradox, means the measurement of a coastline is dependent on the ruler used, an entanglement of instrument and measurement. As rising sea levels encroach on physical coastlines, they are also impacting legal baselines, shifting national terrestrial and maritime borders inland posing existential dilemmas to island and low-lying nations. This paper examines how the concept of sea level was constructed scientifically and is enrolled in the legal demarcation of territorial borders, with the goal of examining how sea level rise politically marks a climatically changing world.