The rate of sea level rise along the US Atlantic coast is greater now than at any time in the past 2,000 years and shows a consistent link between changes in global mean surface temperature and sea level, according to a new open-access study published in the journal Proceedings of the National Academy of Sciences (PNAS).
The research, funded by the National Science Foundation (NSF), was conducted by Andrew Kemp, Yale University; Benjamin Horton, University of Pennsylvania; Jeffrey Donnelly, Woods Hole Oceanographic Institution; Michael Mann, Pennsylvania State University; Martin Vermeer, Aalto University School of Engineering, Finland; and Stefan Rahmstorf, Potsdam Institute for Climate Impact Research, Germany.
Kemp and colleagues developed the first continuous sea-level reconstruction for the past 2,000 years, and compared variations in global temperature to changes in sea level over that time period. The team found that sea level was relatively stable from 200 BC to 1,000 AD. In the 11th century, sea level rose by about half a millimeter each year for 400 years, linked with a warm climate period known as the Medieval Climate Anomaly. Then there was a second period of stable sea level during a cooler period called the Little Ice Age. It persisted until the late 19th century.
Since the late 19th century, sea level has risen by more than 2 millimeters per year on average, the steepest rate for more than 2,100 years.
To reconstruct sea level, the scientists used microfossils called foraminifera preserved in sediment cores extracted from coastal salt marshes in North Carolina. The age of the cores was estimated using radiocarbon dating and other techniques.
To test the validity of their approach, the team compared its reconstructions with tide-gauge measurements from North Carolina for the past 80 years, and global tide-gauge records for the past 300 years. A second reconstruction from Massachusetts confirmed their findings.
The records were corrected for contributions to sea-level rise made by vertical land movements.
The reconstructed changes in sea level over the past millennium are consistent with past global temperatures, the researchers say, and can be determined using a model relating the rate of sea level rise to global temperature.
Support for the research also was provided by the National Oceanic and Atmospheric Administration, United States Geological Survey, the Academy of Finland, the European Science Foundation through European Cooperation in Science and Technology and the University of Pennsylvania.
Andrew C. Kemp, Benjamin P. Horton, Jeffrey P. Donnelly, Michael E. Mann, Martin Vermeer, and Stefan Rahmstorf (2011) Climate related sea-level variations over the past two millennia. PNAS 2011 doi: 10.1073/pnas.1015619108