Creating a Baseline

A warming climate causes ice at the poles to melt and water in the oceans to expand. The Intergovernmental Panel on Climate Change predicts that global mean sea level could rise by as much as four feet by the end of the century, posing a significant danger to coastal communities around the world.

But as anyone who’s spent time on the beach knows, sea level is not a static, easily measured reference point. Tides, wind, gravity, and many other factors affect the surface level of the sea at any given place and time. As Wilko Graf von Hardenberg argues, “Baselines for heights are invented, derived, and described rather than discovered.” Developing an average sea level was not intended to measure climate change at all—it was to create a reference point for measuring European mountain peaks.

The history of sea level offers a window into the ways that concepts scientists often take for granted have been constructed and evolved over time. Despite being invented for a very different purpose, sea level has now become a useful reference for understanding how human activities are transforming the world.

Read more about how the concept of sea level has changed radically over the centuries.