mean sea level
Quick Summary
Mean sea level (MSL) is the average height of the ocean's surface over a long period, accounting for tidal changes, atmospheric pressure, and wind. It serves as a reference point for measuring terrestrial elevations and submarine depths.1
Globally, mean sea level has been rising. Over the 20th century, the average rate was about 1.2 mm per year, though some periods saw faster increases. This rise is influenced by climate change, leading to increased water volume in oceans due to melting glaciers and ice sheets, and thermal expansion of water as it absorbs heat.12
The measurement of sea level is complex due to Earth's irregular shape. While geoids are used as a reference, local variations can affect accuracy. Recent studies suggest that reliance on geoid models may have led to an underestimate of average sea level rise.2
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