In today’s Academic Minute, Dr. Ben Horton of the University of Pennsylvania reveals what we know about sea level change over the past two millennia.
Ben Horton is an associate professor in the Department of Earth and Environmental Science at the University of Pennsylvania. His Sea Level Research Laboratory is working to increase our understanding of the factors that determined changes in sea level in the past in order to enhance our ability to predict changes in the future. He holds a Ph.D. from the University of Durham.
Dr. Ben Horton – Historic Sea Level Change
One of the primary challenges in studying climate change is reconstructing its history. Scientists must understand the past to have a better sense of the causes and effects of future changes. One of these effects that can have serious societal consequences is sea-level rise. Hotter climate temperatures mean higher seas, and that could spell disaster for coastal communities the world over. Predicting the rate and magnitude of global sea-level rise, as well as its local effects, is a high priority.
Our team of researchers has shown that the rate of sea-level rise along the U.S. Atlantic coast is greater now than at any time in the past 2,000 years. What’s more, we have found a consistent link between changes in the average global surface temperature and sea level over this time period.
We discovered that the sea level was relatively stable from 200 BC to 1,000 AD. Beginning in the 11th century, the sea level rose by about half a millimeter per year for 400 years. This occurred during a warm period known as the Medieval Climate Anomaly. A second period of stable sea level followed, associated with a cooler period called the Little Ice Age that persisted until the late 19th century. Since the late 19th century sea level has risen by more than 2 millimeters per year, which is the steepest rate for more than 2100 years.
To reconstruct these measures of historic sea level, we used microfossils called foraminifera preserved in sediment cores from coastal salt marshes in North Carolina. We estimated the age of these cores using radiocarbon dating and several other complementary techniques. To ensure the validity of this approach, we confirmed our reconstructions against U.S. tidal measurements for the past 80 years, and global tidal records for the past 300 years. We then adjusted the records to account for contributions to sea-level rise made by vertical land movements.
We show that the reconstructed changes in sea level over the past millennium are consistent with past global temperatures, and developed a model that relates the rate of sea-level rise to global temperature. Data from the past help to calibrate and improve our models, which will allow us to better project sea-level rise in the future.