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Horton says that sea level will continue to rise in the 21st century. (Photo: UPenn Dep. of Earth and Environmental Science)

What began as Penn Environmental Science student Andrew Kemp’s PhD thesis turned out to be a scientific breakthrough. You might remember that we briefly mentioned Kemp in the Jan/Feb 2010 Gazetteer.

Kemp’s study, which he coauthored with associate professor Benjamin Horton of Earth and Environmental Science and a team of other researchers, proved that sea level along the East Coast has risen far faster over the last century than at any time in the previous 2,000 years. They also established once and for all that there is a near-perfect correlation between rising temperature and rising sea level.

The study is also the first and only continuous record of sea level changes over the past 2,000 years. Kemp and Horton pieced together the timeline by digging up and dating microfossils in the salt marshes of North Carolina.

“There is a virtually perfect relation between temperature and sea-level,” Horton says.

The paper, which was published in the Proceedings of the National Academy of Sciences, identifies 4 main stages of sea level change over the past two millennia. Between 200 B.C. and 900 A.D., sea level was stable. Between the 10th and 14th century, or “Medieval warm period,” sea level rose. Then it stabilized, and even dropped slightly during the “little ice age” which lasted until the end of the 19th century. Since the Industrial Revolution, both temperature and sea level have been rising.

During this fourth and final stage, Horton says, sea level is rising “far faster than anything over the last 2,000 years.” Whereas most sea-level changes took place over hundreds of years, a very rapid rise in sea level occurred between the 1860 and the 1890, Horton says – around the time of the industrialization.

As temperatures continue to rise in the 21st century, Horton says, “It doesn’t take a rocket scientist to figure out that sea levels are going to rise in the 21st century.”

This study “was based upon a societal need,” Horton says.

Scientists have identified a rise in sea level since they began collecting sea level data beginning in the early 20th century. Horton explains. But no previously existing data proved that the trend held up thousands of years ago.

It took a lot of tricky detective work, and “it took Andy five years of his life,” Horton says.

The salt marshes of North Carolina are home to several species of microscopic organisms called foraminifera. Different foraminifera thrive in different conditions – some like to live in freshwater areas away from where the ocean tides hit the marsh. Others prefer brinier environments closer to the tides.

Kemp and Horton extracted foraminifera fossils and radiometrically dated them to figure out where the tide was during different time periods. For further accuracy, says Horton, they used historical knowledge – core samples from the time of European colonization, for example, contained traces of pollen from the settlers’ agriculture.

The implications of this study are groundbreaking, according to Horton. It will allow climate modelers to more accurately predict future sea level changes. In turn, more accurate models will help us decide on strategies to cope as sea level continues to rise. “If you’re going to tell people that sea level is going to rise, that people need to evacuate, that [existing] highways and military will be unusable,” Horton says, you need sound data to back you up.

— Maanvi Singh

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