Traces a commonplace average—sea level—from its origins charting land to its emergence as a potent symbol of global warming.
 
A steady drumbeat of news reports warns of rising sea levels spurred by climate change. Waters inch ever higher around islands and coasts, radically altering delicate ecosystems and threatening the communities who live there. The baseline for these accounts—sea level—may not seem remarkable, given its long-time use as a measure of altitude. But as Wilko Graf von Hardenberg reveals in this sweeping book, the history of this type of measurement is intertwined with national ambitions and rooted in an evolving relationship between people and the ocean. Mean sea level is not a natural occurrence—it is the product of evolving technologies and those who employ them.
 
Sea Level provides a detailed and innovative account of how mean sea level was first defined, how it became a prime reference point for surveying and cartography, and how it emerged as a powerful mark of humanity’s impact on the earth. With Hardenberg as our guide, we traverse the muddy spaces of Venice and Amsterdam, the coasts of the Baltic Sea, the Panama and Suez canals, and the Himalayan foothills. Born out of Enlightenment studies of physics and quantification, sea level became key to state-sponsored public works, colonial expansion, Cold War development of satellite technologies, and acknowledging the climate crisis. Mean sea level, Hardenberg reveals, has always been contingent on people, places, and politics. As global warming transforms the globe, Hardenberg reminds us that a holistic understanding of the ocean and its changes requires a multiplicity of reference points.
 
A fascinating story that revises our assumptions about land and ocean alike, Sea Level calls for a more nuanced understanding of this baseline, one that allows for new methods and interpretations as we navigate an era of unstable seas.