suggests that coastal wetlands throughout the nation would be vulnerable to such a rise, with the 

 possible exception of areas with large tidal ranges or substantial terraces two or three meters 

 above sea level. 



Basic and applied research on the ability of wetlands to adjust to rising sea level would be 

 valuable. Because sea level rose one meter per century on average from 15,000 B.C. until 5,000 

 B.C., it may be possible to better assess the response of wetlands to such a rise in the future. 

 Research on how to artificially promote vertical accretion or control water levels is also import- 

 ant. Such research could benefit coastal states throughout the nation in the long run, although 

 the short-run benefits of protecting Louisiana's wetlands— 40 percent of the total— suggests that 

 such research should be initiated soon. 



When is the appropriate time to respond to the potential loss of wetlands to a rising sea? If 

 technical solutions are possible, it might be sufficient to wait until sea level rise accelerates. 

 Where planning measures are appropriate, a thirty- to fifty-year lead time might be sufficient. 

 Where policies are implemented that will determine the subsequent vulnerability of wetlands to 

 sea level rise, it would be appropriate to consider sea level rise when those decisions are made. If 

 society intends to avert a large rise in sea level, a lead time of fifty to one hundred years may be 

 necessary. 



Wetland protection policies and related institutions such as land ownership are currently 

 based on the assumption that sea level is stable. Should they be modified to consider sea level 

 rise today, after the rise is statistically confirmed, or not at all? This question will not only require 

 technical assessments, but policy decisions regarding the value of protecting wetlands, our 

 willingness to modify activities that destroy them, and the importance of preparing for a future 

 that few of us will live to see. 



NOTES 



1 Several reviewers suggested that these figures may overstate the decline in wetland loss because 



they exclude conversion for agriculture and other nonregulated wetland destruction. 



2 U.S. Fish and Wildlife Service, Charleston, South Carolina Office, personal communication, 



March 1986. 



3 This curve shows the concentration for Mauna Loa, Hawaii, which is sufficiently remote to 



represent the average northern hemispheric concentration. Measurements at the South Pole 

 suggest that the concentration for the southern hemisphere lags at most a couple of years, 

 since most of the sources are in the northern hemisphere. 



4 Studies on the greenhouse effect generally discuss the impacts of a carbon dioxide doubling. By 



"effective doubling of all greenhouse gases" we refer to any combination of increases in the 

 concentration of the various gases that causes a warming equal to the warming caused by a 

 doubling of carbon dioxide alone over 1900 levels. If the other gases contribute as much 

 warming as carbon dioxide, the effective doubling would occur when carbon dioxide 

 concentrations have reached 450 ppm, 1.5 times the year-1900 level. 



5 These estimates did not consider meltwater from Antarctica or ice discharge from Greenland. 



6 Low marsh is found below mean high tide, which is defined as one-half the tidal range above sea 



level; high marsh extends up to the spring high tide, generally less than three-quarters of a 

 tidal range above sea level; and transition wetlands are somewhat higher. 



7 Personal communication. U.S. Fish and Wildlife Service, Charleston Office. The estimates 



exclude forested wetlands and freshwater marshes, which are cleared for agriculture and 

 silviculture. 



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