The water is rising but not at the same rate everywhere

Ben Horton
Benjamin Horton has established the sea level off the New Jersey coast for the past 2,500 years. He has also surveyed the 90 most prolific researchers on global sea level to help us understand what sea level may be in 100 and 200 years.
Benjamin Horton
Most marine researchers consider it a fact that sea levels are rising. But few can agree on how high or how fast that is happening. Benjamin Horton is trying to bridge the gap between recent, short-term instrumental measurements of sea level and long-term reconstructions of historic sea levels, in the hope of informing current efforts to cope with rising sea levels.

Horton, a professor at the Institute of Marine and Coastal Sciences in the School of Environmental and Biological Sciences, and several co-authors recently published two papers in Quaternary Science Reviews regarding sea level. The first measures sea levels for the coast of New Jersey going back 2,500 years.The second is a survey of the scientists who have written most on the subject to find out where they think global sea levels are going in the next 100 and 200 years.

Horton, a native of England, is a graduate of the University of Liverpool who received his Ph.D. at the University of Durham. He was a professor at the University of Pennsylvania before joining the Rutgers faculty this semester. Rutgers Today asked Horton what the past 2,500 years of sea level measurements portends for New Jersey’s future, and why he and his co-authors asked their most prolific colleagues about their future projections.

Rutgers Today: In your paper dealing with sea level off the coast of New Jersey for the past 2,500 years, you and your co-authors conclude that sea level varied – down about 9 centimeters in the 750 years from 500 B.C.E. to the third century C.E.; up by about 30 centimeters in the 500 years from the third to the eighth century; down 13 centimeters from the eighth to the 19th century. Since then, you and your co-authors say, sea level off our coast has risen about 50 centimeters in 160 years. What does this tell you about our current situation and the future?

Horton: We’ve shown that the rate of sea level rise along the New Jersey coast is greater now than at any time in the past 2,500 years. This five-fold increase in the rate of rise can be attributed to climate change through the melting of land ice and the thermal expansion of ocean water. We also discovered that historic sea level varied in response to climate change. The data we have collected from the past help to calibrate and improve our models, which will allow us to better project sea level rise in the future.

Rutgers Today: Has no one ever tried to measure New Jersey sea level back 2,500 years before?

Horton: There have been previous studies of former sea levels, but we were the first group to produce continuous records of former sea levels. We did this by studying the fossil remains of tiny sea creatures called foraminifera, preserved in sediment cores from coastal salt marshes of New Jersey.

Rutgers Today: Why did you and your co-authors think it was necessary to survey other scientists on global sea level rise?

Horton: We thought the public should know what the people who know most about sea-level rise – that is, the people who’ve studied and written about it most – think sea-level rise will look like over the next 100 and 200 years. Sea-level rise threatens hundreds of millions of people who live near the coast, their economies and their static infrastructure. We report the largest elicitation on future sea-level rise conducted from 90 objectively selected experts from 18 countries.

Rutgers Today: And what did you find?

Horton: In  best-case scenario where warming is limited to 2ºC beyond pre-industrial levels, experts predicted about half a meter of rise by 2100 and between 0.6 and 1 meter by 2300. In a high-emissions scenario with 4.5ºC of warming, expert predictions were even more aggressive: 0.7 to 1.2 meters by 2100 and 2 to 3 meters by 2300. Land level changes, just as sea level does. The melting of glaciers, geological processes and people’s use of water resources all vary regionally. Some areas of the U.S. Atlantic coast are already experiencing rates of sea-level rise greatly in excess of the global average.