- Causes of Future Sea Level Rise
- Elevation Maps
- Will we really lose all that land?
- Sea Level Rise Planning Maps
Along almost the entire U.S. coast, sea level is rising—and the rate of that rise is expected to accelerate in the coming decades. Even today, rising sea level is inundating low-lying lands, eroding beaches, exacerbating coastal flooding, and increasing the salinity of estuaries and aquifers.
Over the last several thousand years, shallow-water estuaries have gradually submerged tidal wetlands, which in turn have survived by migrating inland, onto low-lying coastal plains (see Figure 1). Barrier islands and other beach ecosystems have also remained intact by migrating inland. In areas with few if any people, floodplains and tidal ecosystems will probably continue to move inland as sea level rises. In developed areas, however, human activities will complicate—or perhaps prevent—this landward migration.
Figure 1. Evolution of a Marsh as Sea Level Rises. Tidal wetlands are found where the elevation of the land is between high and low tides, with tidal marshes generally above mean sea level and tidal flats below mean sea level. (a) When sea level was rising rapidly, tidal wetlands tended to be a narrow fringe along the shore, determined by tide range and the slope of the land, as both the landward and seaward boundaries migrated inland. But vertical accretion through sedimentation and peat formation have enabled wetlands to keep pace with the relatively slow rate of sea level rise during the last several thousand years. As sea level rose, the landward boundary migrated inland as wetlands formed on newly flooded lands; but the seaward boundary of tidal wetlands did not retreat to the same extent, and the area of tidal wetlands increased. (b) Today, the area of tidal wetlands—i.e., the land between the high and low tide shorelines—is much greater than the amount of dry land within a similar elevation range above the high tide shoreline. Yet there is a limit to vertical accretion and the rate of sea level rise with which tidal wetlands can keep pace. (c) If the sea rises more rapidly, most of the existing tidal wetlands will be lost and the total area of tidal wetlands will decline to the narrow fringe determined by the tide range and slope of the land. (d) Finally, in places where developed lands along the shore are protected from tidal inundation, new wetlands may not form inland and almost all tidal wetlands may be lost. Alternatively, (c) if the development is subject to a rolling easement, then the people who live along the shore will have to relocate and the wetlands will be able to migrate inland. Because the tidal wetlands support fish and wildlife, loss of tidal wetlands could cause populations of birds and fish to decline or relocate.
Communities can respond to sea level rise by any of three or four pathways (See Box 1):
- Shore Protection
- Shoreline armoring. Protect land and buildings from erosion and flooding using dikes, seawalls, bulkheads, and other hard structures. Wetlands and beaches are eliminated as they are squeezed between the rising sea and the shoreline armoring.
- Elevation of land surfaces. Elevate land and buildings as the sea rises. Efforts to protect oceanfront communities usually involve beach nourishment, which elevates the surface of the beach. In theory, the land surfaces of wetlands can also be elevated, though shore protection projects along wetland shores rarely do so.
- Accommodation. Do not try to prevent tidal inundation, erosion, or flooding. But instead of moving people out of harm's way, develop coping strategies that enable continued human habitation in spite of the increased hazards. Wetlands and beaches migrate inland, though they may be impaired by the presence of homes on pilings.
- Retreat. Allow wetlands, beaches, and other coastal habitats to migrate naturally as the sea encroaches inland; move people out of harm's way; and prevent new construction in vulnerable
Because accommodation would rarely be sustainable, the fundamental question is: Which communities will be protected and where will people have to retreat?
Beach nourishment is common along developed ocean shores, and shoreline armoring is common along developed estuarine shores. Although retreat often occurs in undeveloped areas, it is uncommon along developed ocean beaches and very rare along developed estuarine shores. Shore protection is common because it generally costs less than what the protected property is worth. But protecting all developed lands from a rising sea would eventually eliminate tidal wetlands, destroy ocean habitat through dredging, expose millions of people to the hazards from living below sea level, and become economically unsustainable in many areas where it initially seemed successful.
What can society do if individual communities and property owners are inclined to protect more land than would be in society's long-run interest? Logically, there are three ways to limit the portion of our coast eventually subject to shore protection:
- Setbacks. Prevent development of some lands vulnerable to sea level rise, either through regulation or by purchasing land (or development rights) from the current owners.
- Rolling easements. Make no effort to restrict land use but prevent shore protection of some coastal lands either through regulation or by transferring any right to hold back the sea from owners inclined to do so to organizations that would not.
- Laissez-faire. Make no effort to prevent either development or shore protection, but curtail government subsidies for both, and hope that eventually the forces of nature and economics will lead owners to allow their lands to be submerged.
Each way is appropriate in some circumstances.
tolerate setbacks as long as they can build somewhere on their property. Thus
setbacks can be practical where parcels are large or the land is steep enough so
that each lot can have a building site high enough to be safe for the next few
centuries. But in most places with setbacks, development is only set back by at
most a few hundred feet or enough to keep a home out of harm's way for a few
The laissez-faire approach is based on the assumption that investors are more likely to appropriately manage known risks if they bear all of the burdens of bad decisions and reap all of the rewards of good decisions. This approach can reduce eventual shore protection in places where government subsidies would otherwise fund shore protection or coastal development. The Coastal Barrier Resources Act removed federal subsidies for certain barrier islands, causing some to remain undeveloped and reducing the likelihood of shore protection for several that have been developed without the subsidies. Some ocean beach communities have funded their own shore protection or would do so if federal and state subsidies were unavailable. Other oceanfront communities are unlikely to be protected without public funds; so a laissez-faire approach would reduce the extent of beach nourishment along the ocean. But along estuaries, private landowners generally pay for shore protection. Therefore, laissez-faire is unlikely to provide much vacant land for a gradual upslope migration of wetlands and beaches along estuarine shores. Planners view shore protection as likely for at least 60 percent of the low land along the Atlantic coast if sea level rises three feet in the next century. Many landowners will eventually decide to yield their lands to the sea, as shore protection costs escalate, but only after interim shore protection have blocked the inland migration of wetlands and compromised use of the beach.
 See, e.g., NOAA (National Oceanic and Atmospheric Administration), Sea Level Variations of the United States 1854–1999 (NOAA Technical Report NOS CO-OPS 36, 2001). This report and subsequent updates displayed on NOAA's website. Available at: http://tidesandcurrents.noaa.gov/sltrends/sltrends.shtml.
 See, e.g., Intergovernmental Panel on Climate Change, Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change 7 Table SPM.1; id at 13 Table SPM.3, and id. at 820 Table 10.7 (2007).
 Climate Change Science Program, Coastal Sensitivity to Sea Level Rise: A Focus on the Mid-Atlantic Region 2 (U.S. Environmental Protection Agency 2009) [hereinafter CCSP].
 Intergovernmental Panel on Climate Change, Climate Change: The IPCC Response Strategies, 146–149 (1990).
 If people were not moved out of harm's way as sea level rises, buildings that are in low-lying areas today would eventually be standing in open water. There is probably a limit to the number of dock homes a given community would tolerate.
 See, e.g., James G. Titus, Rising Seas, Coastal Erosion, and the Takings Clause: How to Save Wetlands and Beaches without Hurting Property Owners, 57 Md. L. Rev. 1281, 1308–1318 (1998) [hereinafter Maryland Law Review]. That article used the phrases deferring action instead of laissez-faire and preventing development instead of setbacks. See also IPCC, supra note 4, at 147 (using the terms preventing development, planned phaseout, and no direct government role).
 See notes 293–300 and accompanying text.
 See J.G. Titus, R. Park, S.P. Leatherman, R. Weggel, M. Greene, P. Mausel, M. Treehan, S. Brown, C. Gaunt, & G. Yohe, Greenhouse Effect and Sea Level Rise: The Cost of Holding Back the Sea , 19 Coastal Mgmt. 171, 189–92 & Tables 2 and 9 (1991).
 16 U.S.C. §3501 et seq.
See, e.g., Environmental Research Letters, infra note 14,Table S3 (projecting that 26 miles of ocean shoreline along developed barrier islands covered by Coastal Barrier Resources Act in Currituck, Hyde, and other counties are less likely to be protected than similar barrier islands not covered by the act) and id.Table S5 (concluding that being covered by the Coastal Barrier Resources Act reduces the likelihood of shore protection from almost certain to likely, based on interviews with local planners).
 See, e.g., NOAA Coastal Services Center, Beach Nourishment: A Guide for Local Government Officials, section on Federal Cost Participation (undated), http://www.csc.noaa.gov/beachnourishment/ html/human/socio/shares.htm, cited April 1, 2011 (discussing sources of beach nourishment funding in Florida which include special taxing districts) and Carteret County, North Carolina, Adopted Budget 2011–2012 222 (mentioning Salter Path Special Taxing District for Beach Nourishment).
 E.g., J.G. Titus, D.E. Hudgens, D.L. Trescott, M. Craghan, W.H. Nuckols, C.H. Hershner, J.M. Kassakian, C.J. Linn, P.G. Merritt, T.M. McCue, J.F. O'Connell, J. Tanski, & J. Wang, State and Local Governments Plan for Development of Most Land Vulnerable to Rising Sea Level along the U.S. Atlantic Coast 4 Environmental Research Letters 044008 V (2009).
 Cf. CCSP, supra note 3, at 87, 102, and 149 (questioning the sustainability of shore protection).
This page contains a section from: James G. Titus, Rolling Easements, U.S. Environmental Protection Agency. EPA-430-R-11-001 (2011). The report was originally published by EPA's Climate Ready Estuary Program in June 2011. The full report (PDF, 176 pp., 7 MB) is also available from the EPA web site.
For additional reports focused on the implications of rising sea level, go to Sea Level Rise Reports.