How much is Delaware Bay's sea level rising?

A foot.

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.

The University of Pennsylvania's Benjamin P. Horton, a prominent sea-level researcher, has analyzed historic trends.

Since 1900, sea level in the state has been rising at about three to four millimeters a year - double to triple the rates of the last 6,000 years.

Scientists know the land isn't sinking any faster. So the ocean has to be increasing in volume. How is it happening? "Because you add water from ice, or the ocean water warms up," Horton said. "Both of those require an increase in air temperature."

Over the last century, global mean temperature has risen about one degree Centigrade. Many researchers expect the rate of sea-level rise to speed up. - Sandy Bauers


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