Coastal Services Center

The slow rising of our world's seas has been a distant threat for coastal resource managers, one that is difficult to predict, and therefore address. The effects of sea level rise, however, are being felt along Maryland's shores, and the state coastal program has made it a priority to develop policies to address the issue.

"It's really serious," says Zoë Johnson, a National Oceanic and Atmospheric Administration (NOAA) Coastal Management Fellow with the Maryland Coastal Zone Management Division. "The biggest impacts we are seeing are erosion and wetlands submergence, and both are already very prevalent and very serious."

Maryland began looking at the issue of sea level rise in the 1980s and conducted numerous studies "looking at the issue and defining what the range of impacts would be," Johnson says. While the studies offered general policy response options, such as "no action, retreat, accommodate, or protect," there had been little effort to "move the policy issues forward or develop response strategies." In 1998, the state coastal program applied for and received a NOAA fellow to specifically address the policy issues relating to sea level rise. Johnson is working with the state to develop a sea level rise response strategy that is built around three components: a shoreline characterization, a policy analysis, and ongoing public input and outreach. The strategy is scheduled to be complete this fall.

Globally, the sea is rising at an average of about 1.5 millimeters per year, says Curt Larsen, research geologist with the U.S. Geological Survey (USGS), which is studying sea level rise in the Chesapeake Bay. Tide gauges for the Chesapeake Bay, as well as the entire Mid-Atlantic coast show, the sea is rising at a rate twice that of the worldwide average.

"Let's say that 3 millimeters a year is an inch a decade," Larsen explains. "We are working on low-lying areas of Chesapeake Bay that have an elevation of three feet above sea level and the actual slope is very low. An inch may result in the loss of several thousand feet of marsh or lowlands. People don't think an inch a decade is very much, when in fact, it can be really significant."

In various parts of the Chesapeake Bay, scientists are finding marshes that cannot keep up with the rate of sea level rise, Johnson says. Instead of migrating landward as the water rises, wetlands are becoming "submerged or lost." A University of Maryland study shows that about 3,460 acres of Blackwater Marsh were converted to open water between 1938 and 1989. While other variables were impacting the system, sea level rise is thought to be one of the primary factors driving the breakup of the marsh.

Erosion related to sea level rise was first documented in Maryland in 1914 as Sharps Island went from 438 acres in 1848 to 53 acres in 1910. "Today it's totally gone. In the same time period, James Island went from 976 acres to 490 acres, and in 1994 measured 92 acres. James Island had homes, a store, two schools—there's nothing on it now," Johnson says.

Sea level rise isn't just a problem in Maryland, says Mark Schenewerk, an astronomer with NOAA's National Geodetic Survey, which is helping to research ecosystem health and land loss in the Chesapeake Bay. "Communities all along the coast should always be aware of this issue, and I think it would be worth their while to make some effort to understand what the sea level rise is locally."

The causes of sea level rise, Schenewerk explains, are "difficult to discriminate. Sea level rise is a mix of changes on the surface of the earth, as well as changes on the surface of the water."

One of the causes of sea level rise occurred about 20,000 years ago, Larsen says. During the last ice age, water from the oceans fell as snow onto the continents, where it was stored as glacial ice. As the glaciers grew, sea levels worldwide fell, exposing the continental shelf. When the ice began to melt, water flowed back into the ocean basins, rapidly at first, but slowing down and continuing over about the past 6,000 years. He adds that there is disagreement among scientists about whether global warming due to human impacts is speeding the rate at which the glaciers are melting today, thereby increasing the rate of sea level rise.

Another factor in sea level rise is "post glacial rebound." Schenewerk explains that the weight and mass of the glaciers was "sufficient to deform the earth's crust. The mantle material beneath that part of the crust was forced to move outwards forming a bulge around the periphery of the ice sheet." As the ice melted the land underneath began "rebounding, recovering its original shape." He notes, "The area where the bulge was is collapsing to this day," and is causing a small fall in elevation all along the East Coast from New York to South Carolina. Sediment compaction resulting from the pumping of underground oil or water is another possible factor contributing to land subsidence.

"In some sense it doesn't matter what the cause is for sea level rise. The fact is that the sea level is rising and communities need to understand the factor or combination of factors that may impact them, and adjust and adapt," Schenewerk says.

Maryland is utilizing existing studies and literature to complete its shoreline characterization, which will "generally explain the range of impacts," Johnson says. "Maryland has a diverse coastal environment with a full range of coastal types, so that translates into a range of impacts. We're trying to break the state into coastal environments and discuss what the range and impacts would be." Existing literature is also being used to explore what the appropriate response strategies would be to address sea level rise in different environments at both the local and state levels. Extensive public outreach is being conducted, which Johnson says is "crucial to be doing along the way. Getting people to realize there is a problem and getting information to local governments that are working to address the problem at the local level is very important."

Johnson also has had the opportunity to work with the state to "help move the issue forward." With sea level rise as the impetus, the state's governor appointed a shore erosion taskforce that has recommended a regional comprehensive shore erosion control plan. The state recently conducted an issue forum on climate change looking at the impacts on the Chesapeake Bay watershed, and a comprehensive management plan was developed for an area National Estuary Program that "integrates sea level rise and coastal hazards issues into coastal management program language."

"I think we are moving the state in the right direction," Johnson says. "Maryland is involved in this before a lot of states because we're seeing problems. It's not hard to convince people there's a problem when you show them pictures of the islands. Clearly there are areas we need to improve on, but I think the strategy will target those, and address them, and make us even more resistant. There is a critical need to move the issue forward."

For more information about Maryland's sea level rise response planning, contact Zoë Johnson at (410) 260-8986, or zjohnson@dnr.state.md.us. For more information about the sea level rise research in Chesapeake Bay, point your browser to http://pubs.usgs.gov/factsheet/fs102-98/. For more information about sea level rise in the nation, point to http://www.gcrio.org/.