The Heat Is Online

US Atlantic Sea Levels Rising Faster than Any Times in 2000 Years

Sea-levels rising at the fastest rate in 2100 years

 Research along U.S. Atlantic Coast pins sea level change to global warming

The Summit County Voice, June 23, 2011

SUMMIT COUNTY —The romantic house that was the setting for the bed-and-breakfast scenes in the 2008  film Nights in Rodanthe may soon be swallowed up by the ocean, as sea levels along the U.S. Atlantic coast continue to rise in response to climate change.

A research team funded by the National Science Foundation and several other organizations is reporting 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. The study shows a consistent link between changes in global mean surface temperature and sea level.

“Having a detailed picture of rates of sea level change over the past two millennia provides an important context for understanding current and potential future changes,” said Paul Cutler, program director in National Science Foundation’s Division of Earth Sciences.

“It’s especially valuable for anticipating the evolution of coastal systems in which more than half the world’s population now lives,” he said.
During the last 2,000 years, the climate has been relatively stable. The EPA climate change website describes three periods of  departures from this stability: The Medieval climate anomaly, the little ice age, and the industrial era.

In the Medieval Climate Anomaly, evidence suggests Europe, Greenland and Asia experienced relative warmth for several hundred years around 1000 A.D. A wide variety of evidence supports the global existence of a Little Ice Age (this was not a true ice age since major ice sheets did not develop) between about 1500 and 1850. An additional warm period has emerged in the last 100 years, coinciding with substantially increasing emissions of greenhouse gases from human activities.

Andrew Kemp, of Yale University, and his 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. Their research findings are published this week in the Proceedings of the National Academy of Sciences.

The team found that sea level was relatively stable from 200 BC to 1000 A.D. In the 11th century, sea level rose by about half a millimeter each year for 400 years, linked with the medieval climate anomaly. There was a second period of stable sea level during the little ice age, which 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.

“Sea-level rise is a potentially disastrous outcome of climate change,” said Benjamin Horton of the University of Pennsylvania, “as rising temperatures melt land-based ice, and warm ocean waters.”

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.

“Data from the past helped calibrate our model, and will improve sea level rise projections under scenarios of future temperature increases,” said Stefan Rahmstorf of Potsdam Institute for Climate Impact Research in Germany.

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. 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.