That's how much sea level has risen in the Delaware Bay in the last century, measurements show.
Two factors are driving the rise: The biggest reason is that the volume of the ocean is increasing - an event scientists say is related to warming water, caused by a warming planet, brought on in turn by higher levels of carbon dioxide in the atmosphere.
The other factor is that the land is sinking. About 20,000 years ago, when glaciers extended roughly to the top of New Jersey, the land to the south was pushed up. Now it's subsiding again.