Rising Waters Imperil Coastal Property
Erosion can destroy coastal property, such as this beach house located along North Carolina's Outer Banks. (NOAA)
The historic Cape Hatteras Lighthouse was built in 1870 on a strip of sand more than a quarter mile from the water's edge. It was thought to be safe from the sea's force. For almost a century, it was. But by the 1970s, the slow rise of the ocean's waves threatened its foundation. The lighthouse was a mere 160 feet from the water's edge.
To preserve the landmark, the nation's tallest brick lighthouse, the National Park Service moved it more than half a mile inland—an engineering feat that took a decade to plan and cost taxpayers a whopping $10 million.
Beach-front owners on the Outer Banks are losing ground, too. People from all over visit the shores, which are now lined with beach houses, explains Doug Stover, cultural resource manager of Cape Hatteras National Sea Shore. "What's happening," says Stover, "is that they're losing more sand so they're trucking in more sand ... to preserve their homes."
How global warming raises sea levels
Higher seas are one of the most certain consequences of global warming. Why? For one, melting glaciers and polar ice sheets add water to our oceans. Glaciers store water on land. When these huge ice masses melt into the oceans, it adds volume and water levels rise. (The concept is simple to demonstrate. Add a bunch of ice cubes to a glass of water that's already full to the brim and it will overflow. That extra water is like the extra ocean water from melting glaciers.)
On top of that, water expands as it gets warmer. So as the temperature rises, the same amount of water takes up more space. This raises sea levels higher.
Risks multiply as sea levels rise
Rising sea levels are a double whammy for the coastline. Not only do they flood the land, but higher ocean waves also erode more coastline. Coastal residents face a constellation of concerns: higher flood risk, more property damage and higher insurance rates. (Higher insurance rates can also cost taxpayers, since the federal government subsidizes flood insurance for many coastal properties.)
The lighthouse's situation illustrates another way in which global warming puts coastal property owners in double jeopardy. When scientists from the National Academies of Science assessed the lighthouse's troubles, they found two main reasons for the eroding foundation: rising sea levels and hurricanes. Hurricanes are expected to get stronger as global warming worsens. (More about hurricanes and global warming.)
On the health front, rising seas also contaminate fresh water supplies with salty water in places like Philadelphia, New York City (its drought supply), and much of California's Central Valley.
Trouble throughout the country
Over the twentieth century, the seas rose between four and eight inches, ten times the average rate of the last 3,000 years. This alarming trend threatens all of the nation's coastal communities, where more than half the U.S. population lives. Other parts of the globe are vulnerable, too. More frequent and extreme flooding due to sea-level rise threatens low-lying areas near the mouths of the Nile in Egypt, the Mekong in Vietnam and Cambodia, and Ganges and Brahmaputra in Bangladesh and other rivers around the world. Italy's famous sinking city of Venice, which is surrounded by water and whose ground underneath is subsiding like Louisiana's, is also particularly vulnerable.
Scientists project that sea levels will continue to rise as a result of human-produced greenhouse gas pollution and could reach an additional 3.5 inches to 3 feet by the end of the century, with the possibility of even larger rises should the ice sheets on Greenland and Antarctica disintegrate. A foot of higher waters could destroy anywhere from 50 to 1,000 feet of horizontal shoreline in many parts of the U.S., depending on the slope of the coastline and other factors. Here is a snapshot of different areas suffering from rising seas.
One-third of the marsh at the Chesapeake Bay's Blackwater National Wildlife Refuge is now submerged.
The edges of mangrove forests in Bermuda are lined with recently drowned trees.
The loss of wetlands, Mother Nature's first defense against storms, put Louisiana's coastline and New Orleans in a precarious position. About every thirty minutes an area of land the size of a football field in the Mississippi Delta vanishes and is replaced by open water. (While global warming is contributing to rising sea levels, part of Louisiana's land loss is due to subsidence from both natural and man-made causes.)
On the West Coast, flat, low-lying coastal areas such as the San Francisco Bay area and parts of the L.A. area also vulnerable.
If sea level continues to rise, thousands of square miles of land in densely populated areas such as the eastern U.S. may be lost in a century or two, and flooding during storm surges will worsen. Construction of physical barriers such as seawalls would be expensive and in some cases infeasible.
What You Can Do
Small changes to your daily routine can add up to big differences in helping to stop global warming.
Sources
Bellassen, Valentin; Chameides, Bill. High Water Blues 2005 Update. Environmental Defense, 2005. www.environmentaldefense.org/documents/
Chameides, Bill; Wang, James. Global Warming's Increasingly Visble Impacts. www.environmentaldefense.org/documents/
Image: Richard B. Mieremet, Senior Advisor, NOAA OSDIA