Weather Talk: Why the oceans rise
The level of the sea on Earth has risen about 8 inches since late in the last century. A more substantial rise is forecast for the present century.
Most people unfamiliar with the science of sea level rise are unaware that the level of the sea, and the rate of rise, varies from place to place. There are three reasons the sea level rises.
The reason easiest to understand is the increase of water. When ice not presently in the sea melts, that volume of water is added to the sea, causing it to rise.
About half of the rise since the 1800s is due to thermal expansion. As the temperature of the ocean rises, it expands. Because the ocean has not been warming uniformly, the ocean level has come up more in some places than in others.
Changing ocean currents associated with Climate Change are further capable of forcing water levels higher in some areas.