Climate scientists predict a rise in sea level of a meter or more, over the next 50 or 100 years. The change is predicted to create a variety of problems for the coasts, and for coastal land use policy. One important question, according to a September paper in the journal Environmental Research Letters, is what will be the fate of coastal salt-marsh wetlands that play a vital role in the ocean ecosystem (“ State and local governments plan for development of most land vulnerable to rising sea level along the Atlantic Coast,” by J.G. Titus, et al). When sea levels rise, write EPA scientist Jim Titus and his co-authors, wetlands can get flooded out. The marshes are sometimes able to survive by retreating inland. But this adaptation is limited by development that raises low-lying coastal grades, or by man-made seawalls and other flood protection methods. And based on a multi-year EPA analysis of coastal development patterns, the study reports, "we estimate that almost 60% of the land below 1 meter [less than one meter above sea level] along the US Atlantic coast is expected to be developed and thus unavailable for the inland migration of wetlands." Sea-level rises will be unusually rapid in terms of geologic time, but still relatively slow in terms of human time — allowing landowners plenty of opportunity to prevent the flooding of the low-lying areas. That could protect human uses of the land, but it will also eliminate the potential escape route of the threatened salt marshes. Under current regulations, Titus and his co-authors point out, landowners can build defensive seawall structures at will: "The existing nationwide permit for shore protection authorizes almost any owner of a small- or medium-sized lot to erect a shore protection structure that prevents ecosystems from migrating inland." The paper recommends a reconsideration of this general permit, based on an analysis of the broad ecological implications of preventing wetlands from migrating, instead of the current narrow analysis based on the minor environmental impact the seawall has within its own footprint. But as the study notes, the salt marshes have few options: most of the land adjacent to existing wetlands is already tied up by human activity. "With only 9% of the lowest land set aside for conservation, a large scale migration would require either a halt to construction in most coastal floodplains or an eventual abandonment of many developed areas." Will that happen? The prospect seems unlikely, the authors concede. But the alternative — protecting more and more coastal cities and towns with New Orleans-style civil engineering — is also far from a no-brainer. "A map that shows Miami completely under water may not be as realistic as Miami subjected to a lot of shore protection measures,'' Jim Titus told the Miami Herald (" Study raises new red flag on coastal development," by Curtis Morgan). But those measures, in addition to having environmental costs, will have to be heroic in scale, the scientists warn. Study co-author Daniel Trescott, a planner for the Southwest Florida Regional Planning Council, commented to the Herald, "The thing that is hard to fathom is how are we going to be able to hold back the sea in a massive way in order to keep people at their current locations? The reason we did this [report] was to get people to start talking about what we are going to do.''
