Sea Level 101, Part Two: All Sea Level is ‘Local'

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Visit the NASA page Sea Level 101, Part Two: All Sea Level is ‘Local' 

Excerpt: ...we know sea level on the open ocean isn’t really flat. A number of factors combine to determine the topography of the ocean surface. Global sea level rise is complex as well. To begin with, it has multiple causes, including the thermal expansion of the ocean as it warms, runoff of meltwater from land-based ice sheets and mountain glaciers, and changes in water that’s stored on land. These factors combine to raise the height of our global ocean about 3.3 millimeters (0.13 inches) every year. That rate is accelerating by another 1 millimeter per year (0.04 inches per year) every decade or so.

...“Relative sea level” refers to the height of the ocean relative to land along a coastline. Common causes of relative sea level change include:

  • Changes due to heating of the ocean, and changes in ocean circulation
  • Changes in the volume of water in the ocean due to the melting of land ice in glaciers, ice caps, and ice sheets, as well as changes in the global water cycle
  • Vertical land motion (up or down movements of the land itself at a coastline, such as sinking caused by the compaction of sediments, or the rise and fall of land masses driven by the movement of continental or oceanic tectonic plates)
  • Normal, short-term, frequent variations in sea level that have always existed, such as those associated with tides, storm surges, and ocean waves (swell and wind waves). These variations can be on the order of meters or more (discussed in more detail in our previous blog post).

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