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How does warmer ocean water cause sea level to rise?

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Grinnell Glacier shrinkage — Global warming A series of photographs of the Grinnell Glacier taken from the summit of Mount Gould in Glacier National Park, Montana, in (from left) 1938, 1981, 1998, and 2006. In 1938 the Grinnell Glacier filled the entire area at the bottom of the image. By 2006 it had largely disappeared from this view.

Warmer ocean water causes sea levels to rise primarily through a process known as thermal expansion.12

As the oceans absorb excess heat trapped in the atmosphere by greenhouse gases, the water molecules gain kinetic energy and move more vigorously, causing them to take up more space. This physical expansion of the water increases the total volume of the ocean, which directly raises the height of the sea surface.12

Thermal expansion is a significant driver of global sea level rise, accounting for approximately 30 percent of the annual increase. In addition to this process, ocean warming contributes to sea level rise indirectly by accelerating the melting of glaciers and ice sheets, which releases additional liquid water into the oceans. Together, these factors—thermal expansion and the influx of meltwater—are the primary contributors to the rising global sea level.213