Jennifer Welsh, LiveScience Yahoo News 21 Jun 11;
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.
Historical records
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.
Study details significant sea level rise
Randolph E. Schmid Associated Press Yahoo News 20 Jun 11;
WASHINGTON – Sea level has been rising significantly over the past century of global warming, according to a study that offers the most detailed look yet at the changes in ocean levels during the last 2,100 years.
The researchers found that since the late 19th century — as the world became industrialized — sea level has risen more than 2 millimeters per year, on average. That's a bit less than one-tenth of an inch, but it adds up over time.
It will lead to land loss, more flooding and saltwater invading bodies of fresh water, said lead researcher Benjamin Horton whose team examined sediment from North Carolina's Outer Banks. He directs the Sea Level Research Laboratory at the University of Pennsylvania.
The predicted effects he cites aren't new and are predicted by many climate scientists. But outside experts say the research verifies increasing sea level rise compared to previous centuries.
Kenneth Miller, chairman of the Department of Earth and Planetary Sciences at Rutgers University, called the new report significant.
"This is a very important contribution because it firmly establishes that the rise in sea level in the 20th century is unprecedented for the recent geologic past," said Miller, who was not part of the research team. Miller said he recently advised New Jersey Gov. Chris Christie that the state needs to plan for a sea level rise of about 3 feet by the end of the century.
Horton said rising temperatures are the reason behind the higher sea level.
Looking back in history, the researchers found that sea level was relatively stable from 100 B.C. to A.D. 950. Then, during a warm climate period beginning in the 11th century, sea level rose by about half a millimeter per year for 400 years. That was followed by a second period of stable sea level associated with a cooler period, known as the Little Ice Age, which persisted until the late 19th century.
Rising sea levels are among the hazards that concern environmentalists and governments with increasing global temperatures caused by "greenhouse" gases like carbon dioxide from burning fossil fuels like coal and oil over the last century or so.
Although melting icebergs floating on the sea won't change sea level, there are millions of tons of ice piled up on land in Greenland, Antarctica and elsewhere. Melting that ice would have a major impact by raising ocean levels.
The result could include flooding in highly populated coastal cities and greater storm damage in oceanfront communities.
While the new study does not predict the future, Horton pointed out that it does show "there is a very close link between sea level and temperature. So for the 21st century when temperatures will rise, so will sea level."
Two of his co-authors calculated in an earlier paper that sea level could rise by between 30 and 75 inches by the end of this century. And it might even rise faster than that, Martin Vermeer of Aalto University in Finland and Stefan Rahmstorf of Germany's Potsdam Institute for Climate Impact reported in 2009.
"Accurate estimates of past sea-level variability provide a context for such projections," co-author Andrew Kemp of Yale University's Climate and Energy Institute said in a statement.
Horton's team studied sediment cores from salt marshes at Sand Point and Tump Point on the North Carolina coast to develop their calculations of sea-level change over the two millennia. They analyzed microfossils in the cores and the age of the cores was estimated using radiocarbon dating and other methods.
For the years since tide gauges have been installed, those findings closely track the results from the study, the researchers noted. The study is being published in this week's edition of the Proceedings of the National Academy of Sciences.
While Horton's report is the first to produce a continuous record of the past 2,000 years "other studies show similar changes, especially concerning the acceleration in sea level rise in the 20th century," Miller said.
