Rising seas over the next century will force changes to land management and force governments to ramp up mitigation efforts, U.S. EPA said in a report released today.
"People along the coast are going to have to think differently when they look into the future, because shorelines are not necessarily going to be where they are," said Jim Titus, the study's lead author and an EPA project manager for sea level rise. "What we're saying in this report is that many, perhaps most, organizations need to understand which activities are sensitive to sea level rise and how to change them."
Global warming is very likely the key contributor to sea level rise, causing glaciers to melt and oceans to expand, the report says. Rising seas and stronger storms will increase threats to coastal cities, infrastructure, beaches, wetlands and ecosystems. Ports and the tourism and commercial fishing industries are particularly vulnerable to sea level rise.
The report evaluates three sea level rise scenarios over the next century, focusing on the mid-Atlantic region. Scientists developed models for the evaluations using a combination of 20th-century rates of sea level rise and either a 2-millimeter or a 7-millimeter increase in global sea level.
Using the 20th century sea-rise rate of 3 to 4 millimeters a year in the mid-Atlantic, researchers said sea levels would rise 30 to 40 centimeters by 2100. In the second scenario, they used the 29th-century rate and added 2 millimeters per year, bringing the total sea level rise to 50 centimeters by 2100. For the third scenario, they used the 20th-century rate with a 7-millimeter-per-year acceleration, a total of 100 centimeters by 2100.
The first and second scenarios align with predictions of the Intergovernmental Panel on Climate Change; the third uses higher estimates.
Rapid sea level rise could spur people and wildlife in densely packed coastal areas to quickly migrate landward, the report says. It also could submerge parts of barrier islands and disintegrate wetlands, which are a vital sponge for pollutants and a buffer for storms. A 2-millimeter-per-year sea level rise would stress wetlands, while a 7-millimeter rise would likely destroy them, the study notes. The destruction of wetlands would cause problems in areas that rely on them for flood control against storm surges.
Increased salinity in estuaries and freshwater aquifers could affect drinking water and aquatic species. Also, it is virtually certain that coastal erosion would accelerate under the scenarios, particularly along sandy beaches that dominate the mid-Atlantic coast.
Communities can help guard against sea level rise through shore protection and engineering efforts, the study notes. The impact of sea level rise will, in large part, be determined by the slope of land at the coast. The report suggests that more data are needed to estimate benefits from increasing land elevations.
"You need to start figuring out, do you allow ecosystems to migrate inland where there is human activity?" Titus said. "People want to develop low-lying coastal areas and want to hold back the sea, and yet if you do that, eventually, it is not good for the environment and creates an increasingly risky situation."
Large coastal populations
The size of coastal populations compounds the difficulties of coping with sea level rise.
"You can divide the coastal zone into three areas," Titus said. "The really densely populated areas, it's hard to see giving them up. You have to think about how you're going to protect it. We're not going to give up New York City to sea level rise anytime soon."
In undeveloped areas, communities must decide how to manage eroding land, he added. Development planning will have to be done with sea level rise in mind.
Traditional coastal engineering and current floodplain maps may not be adequate as developers and communities look toward the future, as they are based on current rates of coastal erosion and sea level rise, the report says. Developers and communities will need to consider how to preserve public access to the shore and craft land-use plans aimed at maintaining wetlands, beaches and coastal ecosystems.
Also, there will be a need to retrofit and redesign buildings to help them to withstand weather and sea level changes, the report says. Flood insurance also may have to be revamped.
Coastal managers must ramp up their efforts to plan for sea level rise, the report says. State governments must fund scientific research, conduct an increasing number of analyses and implement policy changes accordingly. Land preservation and building decisions made today could greatly affect communities' fates as the sea encroaches.
Limiting development in coastal areas would allow ecosystems to move inward as sea levels go up, Titus said. He also suggested movable houses that could migrate inland as seas rise. Another option, he said, is filling in eroding areas and elevating homes.
EPA prepared the report with the National Oceanic and Atmospheric Administration and the U.S. Geological Survey. The U.S. Climate Change Science Program commissioned the study.
Click here to view the report.