Sea levels are rising faster than they have been in the last two millennia, new research shows. The swelling seas match up well with historical temperature data, suggesting the warmer it is, the more the sea level rises.
"Sea-level rise is a potentially disastrous outcome of climate change," study researcher Benjamin Horton, of the University of Pennsylvania, said in a statement. "Rising temperatures melt land-based ice and warm ocean waters."
Rising sea levels could threaten coastal cities, with 50 percent of the U.S. population living within 50 miles (80 kilometers) of the coast. The faster sea levels rise, the more difficult it will be for cities to adjust and the more dramatic the erosion of the coastline will get, according to researchers.
Reading sea levels
The team reconstructed sea-level variability off the East Coast of the U.S. over the last 2,000 years from the microfossils (from animals that typically lived in the oceans) found in soil cores from marshes in North Carolina.
The results revealed the height of the seas during particular years, which they then compared with data from tide-gauge measurements from the last 300 years.
They found that sea levels were stable from around 200 B.C. to A.D. 1000, followed by a rise of 0.02 inches (0.5 millimeters) per year for 400 years. After this increase, the sea level held steady through the late 19th century. Sea levels started rising again since then, averaging about 0.08 inches (2 millimeters) a year on average. This is the steepest rise the group has seen in its records, which go back more than 2,100 years.
They then compared this data with historical temperature records. First, they noticed that the sea-level increases that occurred in the 11th century coincided with a warm period known as the Medieval Climate Anomaly. Current sea-level rise seems to coincide with temperature changes, as well.
The data will help researchers understand the Earth's changing climate and oceans in the context of historical changes. It may also help researchers predict how much sea levels will rise with higher global temperatures.
"Scenarios of future rise are dependent on understanding the response of sea level to climate changes," study researcher Andrew Kemp, of Yale University, said in a statement. "Accurate estimates of past sea-level variability provide a context for such projections."
The study was published this week in the journal Proceedings of the National Academy of Sciences.
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