Meretaseme

Meretaseme, or sea level, is the average height of the ocean surface relative to a reference on land. In Estonian, meretaseme translates to “sea level.” Scientists distinguish mean sea level (MSL), the long-term average, from the immediate effects of tides, waves, and storms. MSL provides a baseline for measuring land elevations and for coastal planning.

Sea level is not uniform across the globe. Local sea level results from the combined effects of ocean dynamics (currents, wind, and water temperature and salinity), atmospheric pressure, and the shape of Earth's gravity field, known as the geoid. The observed sea surface at a location is called dynamic sea level and can depart from the global average by several decimeters or more over time.

In addition to ocean processes, vertical movement of the land itself alters relative sea level. Isostatic rebound, tectonic activity, sediment compaction, and groundwater extraction can raise or lower coastlines, independently of the oceans.

Since the late 19th century, global mean sea level has risen due to thermal expansion of warming seawater and the addition of water from melting ice sheets and glaciers. Projections indicate continued rises through the present century, with regional differences driven by ocean circulation and land movement.

Knowledge of meretaseme serves navigation, flood risk assessment, and the definition of vertical datums used in maps and construction. It underpins climate research and informs policies on coastal adaptation and infrastructure resilience.