Thinking in Averages: On the Conceptualization of the Level of the Sea as a Mean

In recent decades mean sea level has become the almost unavoidable reference point of an impending environmental cataclysm. Before that it had been naturalized as the most common, almost intuitive vertical datum. The idea to neatly conceptualize the vertical boundary between land and sea as an average is however a fairly recent one. By all its allure as a global baseline it is also the product of very specific local environmental and cultural conditions. As such it is the outcome of a process of social construction that begun in the early modern period in two very specific, quite muddy regions of Europe: Venice and the Netherlands. In this paper I explore how and why the idea to measure the level of the sea first developed where and when it did, discussing extensively the geographical constraints of its conceptualization. Furthermore I relate how the level of the sea was, around the turn of 1800, rethought as an abstract, averaged version of the different levels that can be physically apprehended along coasts and littorals. I proceed, in other words, in the analysis of a crucial case study in how local measurements were morphed into standardized, discrete, and more legible features to then become global in the wake of Europe’s imperial and colonial ventures.