Fastest Sea-Level Rise in Two Millennia Linked to Increasing Temperatures

An international research team 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 and has shown a consistent link between changes in global mean surface temperature and sea level.

Sea level rise is one of the threats of climate change, as rising temperatures melt glaciers and ice sheets and put coastal populations at risk of flooding. “Scenarios of future rise are dependent upon understanding the response of sea level to climate changes,” said Andrew Kemp, a Yale postdoctoral associate and the lead author of the new study. “Accurate estimates of past sea-level variability provide a context for such projections.”

In the new study, researchers provided the first continuous sea-level reconstruction for the past 2,000 years and compared variations in global temperature to changes in sea level over this time period.

The team found that sea level was relatively stable from 200 B.C. to 1,000 A.D. Beginning in the 11th century, sea level rose by about 1/50 of an inch per year for 400 years, associated with a warm climate period known as the Medieval Climate Anomaly. A second period of stable sea level associated with a cooler era, called the Little Ice Age, persisted until the late 19th century. Since then, sea level has risen by nearly 1/10 of an inch per year on average — the steepest rate for more than 2,100 years.

To reconstruct sea level, the research team used microfossils called foraminifera preserved in sediment cores from coastal salt marshes in North Carolina. The age of these cores was estimated using radiocarbon dating and several other complementary techniques.

The team showed that the reconstructed changes in sea level over the past millennium are consistent with past global temperatures and can be described using a model relating the rate of sea level rise to global temperature.

The research is published in the June 20 issue of the Proceedings of the National Academy of Sciences. Other authors of the paper include Benjamin Horton (University of Pennsylvania), Jeffrey Donnelly (Woods Hole Oceanographic Institution), Michael Mann (Pennsylvania State University), Martin Vermeer (Aalto University School of Engineering), and Stefan Rahmstorf (Potsdam Institute for Climate Impact Research).

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