Sealevel

Sealevel, more commonly written as sea level, or mean sea level (MSL), is the average height of the world’s oceans relative to a reference surface. It is used as a baseline for measuring elevations and coastal landforms. Sealevel is not fixed; it varies regionally and over time due to tides, atmospheric pressure, winds, ocean circulation, and thermal expansion. Short-term fluctuations arise from tides and storms, while longer-term trends reflect climate processes and land motion.

Global sealevel has risen over the past century. Current estimates place the rise since 1900 at about 0.2 to 0.3 meters, with an acceleration in recent decades. The principal drivers are thermal expansion of seawater as it warms and the loss of mass from glaciers and ice sheets in Greenland, Antarctica, and mountainous regions. Other contributions include changes in land water storage and post-glacial rebound. Sealevel is measured with tide gauges and satellite altimeters; local levels are also affected by vertical land motion and gravity field changes.

Impacts from rising sealevel include increased coastal flooding, higher storm-surge risk, shoreline erosion, and saltwater intrusion into freshwater aquifers. Projections for 2100 depend on future emissions and ice-sheet behavior; typical ranges span about 0.3 to 1.0 meters, with higher estimates if large ice losses occur. Adaptation strategies include coastal defenses, managed retreat, and land-use planning that accounts for rising seas and local subsidence.