Most people are surprised to learn that, just as the surface of the Earth is not flat, the surface of the ocean is not flat, and that the surface of the sea changes at different rates around the globe. For instance, the absolute water level height is higher along the West Coast of the United States than the East Coast.
You may have heard the term “global sea level,” which refers to the average height of all of the Earth's ocean basins. "Global sea level rise" refers to the increase in the average global sea level trend.
"Local sea level" refers to the height of the water measured along the coast relative to a specific point on land. Tide stations measure local sea level. "Relative sea level trends" reflect changes in local sea level over time. This relative change is the one most critical for many coastal applications, including coastal mapping, marine boundary delineation, coastal zone management, coastal engineering, sustainable habitat restoration design, and the general public enjoying their favorite beach.