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Greenhouse Effect, Sea Level Rise, and Coastal Wetlands

James G. Titus, ed., 1988. Washington, D.C.: U.S. Environmental Protection Agency. 186 pp. EPA 230-05-86-013.

Greenhouse Effect, Sea Level Rise, and Coastal Wetlands (PDF, 186 pp 4.1 MB) was EPA's first attempt to provide a comprehensive vision of the impact of accelerated sea level rise on wetlands. Because later reports repeat alot of the same information, we also provide some subsequent notes by the report editor for those interested in undertanding how this report relates to other studies.

The report's Summary and its Conclusions are online following the Table of Contents. For additional reports focused on the implications of rising sea level, go to More Sea Level Rise Reports.

List of Chapters

Complete Table of Contents, Summary, and Conclusions (PDF, 7 pp., 375 kb)

1. Sea Level Rise and Wetland Loss: An Overview (PDF, 35 pp., 728 kb)
by James G Titus. See also editor's notes about related reports

2. Charleston Case Study(PDF, 22 pp., 343 kb)
by Timothy W. Kana, Bart J. Baca, and Mark L. Williams. See also editor's notes about related reports

3. New Jersey Case Study (PDF, 25 pp., 450 kb)
by Timothy W. Kana, William C. Eiser, Bart J. Baca, and Mark L. Williams. See also editor's notes about related reports

4. Impacts on Coastal Wetlands Throughout the United States (PDF, 64 pp., 2.6 MB
by Thomas V. Armentano, Richard A. park, and C. Leslie Cloonan. See also editor's notes about related reports

5. Alternatives for Protecting Coastal Wetlands from the Rising Sea (PDF, 2 pp., 21 kb)
by the Office of Wetland Protection, U.S. EPA. See also editor's notes about related reports

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Increasing atmospheric concentrations of carbon dioxide and other gases released by human activities are generally expected to warm the earth a few degrees (C) in the next century by a mechanism commonly known as the "greenhouse effect." Such a warming could raise sea level by expanding ocean water, melting mountain glaciers, and eventually causing polar ice sheets to slide into the oceans. Unfortunately, it is not yet possible to accurately predict future sea level.

Estimates for the year 2025 range from five to fifteen inches above current sea level, while estimates of the rise by 2100 range from two to seven feet. Although the timing and magnitude of future sea level rise is uncertain, there is an emerging scientific consensus that a significant rise is likely.

To further society's understanding of how to rationally respond to the possibility of a substantial rise in sea level, EPA has undertaken assessments of the impacts of sea level rise on economic development, beach erosion control strategies, salinity of estuaries and aquifers, and coastal drainage and sewage systems. Those studies have generally found that even a one-foot rise in sea level has important implications for the planning and design of coastal facilities. This report examines the potential impacts of sea level rise on coastal wetlands in the United States. Coastal marshes and swamps are generally within a few feet of sea level, and hence could be lost if sea level rises significantly. Although new wetlands could form where new areas are flooded, this cannot happen where the land adjacent to today's wetlands is developed and protected from the rising sea. Once built, neighborhoods can be expected to last a century or longer. Therefore, today's coastal development could limit the ability of coastal wetlands to survive sea level rise in the next century.

Chapter I provides an overview of the greenhouse effect, projections of future sea level rise, the basis for expecting significant impacts on coastal wetlands, and possible responses. Chapters 2 and 3 present case studies of the potential impacts on wetlands around Charleston, South Carolina, and Long Beach Island, New Jersey, based on field surveys. Chapter 4 presents a first attempt to estimate the nationwide impact, based on topographic maps. Finally, Chapter 5 describes measures that wetland protection officials can take today. This report neither examines the impact of sea level rise on specific federal programs nor recommends specific policy changes.

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  1. Along undeveloped coasts, a rise in sea level drowns the seaward wetlands and allows new wetlands to be created inland as formerly dry land is flooded. However, for the rise in sea level expected in the next century, the area just above sea level available for wetland creation is generally far smaller than the area of wetlands that would be lost. Along developed coasts, there may not be any land available for wetland creation.
  2. Sea level rise could become a major cause of wetland loss throughout the coastal zone of the United States. Assuming that current rates of vertical wetland growth continue and that economic development does not prevent the formation of new wetlands, a five-foot rise would result in 80 percent losses of wetlands in both the South Carolina and New Jersey case studies. In the preliminary nationwide analysis, a five- to seven-foot rise would result in a 30 to 80 percent loss of coastal wetlands.
  3. The coastal wetlands of Louisiana appear to be the most vulnerable to a rise in sea level. The coastal wetlands of the Mississippi River delta are already converting to open water at a rate of 50 square miles per year because of the interaction between human activities, such as construction of levees and navigation channels, and current relative sea level trends caused by land subsidence. Future sea level rise could substantially accelerate the rate of wetland loss and alter the relative advantages of various options to solve the problem.
  4. The impact of sea level rise on coastal wetlands will depend in large measure on whether developed areas immediately inland of the marsh are protected from rising sea level by levees and bulkheads. In the Charleston case study, protecting developed areas would increase the 80 percent wetland loss to 90 percent for a five-foot rise. In the nationwide analysis, structural protection would increase the 30-80 percent loss to 50-90 percent.
  5. Factors not considered in this report could increase or decrease the vulnerability of wetlands to a rise in sea level. This report does not attempt to estimate the change in rates of vertical marsh growth that might accompany a global warming and rise in sea level.
  6. Federal and state agencies responsible for wetland protection should now begin to determine how to mitigate the loss of wetlands from sea level rise. Outside of Louisiana, the most substantial losses are at least 50 years away. However, today's coastal development may largely determine the success with which wetlands adjust to rising sea level in the future.
  7. The prospect of accelerated sea level rise does not decrease the need to implement existing wetland protection policies. Numerous federal, state, and local programs are being implemented to curtail the destruction of the nation's dwindling coastal wetlands. Some people have suggested that because these policies protect wetlands that will eventually be inundated, the prospect of sea level rise is a justification for relaxing wetland protection requirements. However, even from the narrow perspective of a particular parcel of land, this justification ignores the biological productivity that these wetlands can provide until they are inundated, as well as the value of submerged aquatic vegetation that could develop after they are inundated. Moreover, from the broader perspective, even if particular parcels are flooded, society has options for ensuring the continued survival of wetland communities as sea level rises, such as allowing them to migrate inland or promoting their vertical accretion. By protecting today's wetlands, existing programs are helping to keep those options open.

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Subsequent notes by the Editor
    This report was completed, ready for publication, and approved by EPA's Office of Policy, Planning, and Evaluation by the summer of 1986. The publication review official within EPA's Office of External Affairs (Richard Laska), however, refused to approve publication. He conducted a second peer review, as well as a cross-agency internal review, and found objections by two offices. Howard Marshall (now retired) of Region 4 objected to the report's failure to discuss elevation reference planes, which might lead some people to confuse the national geodetic vertical datum with mean sea level. (A problem that eventually lead to dike failure during Hurricane Katrina). Additional text resolved that concern. Secondly, a member of EPA's Wetlands Office objected to the entire report, for two reasons. He had discussed the matter with professors from Virginia that he knew and trusted, who persuaded him that there was insufficient evidence of sea level rise to justify EPA reports on the subject. Moreover, he feared that people would use the projections of wetland loss from sea level rise as a justification to not protect existing wetlands, since they will all be underwater eventually anyway. Therefore, it was not in EPA's interest to release a report like this.

    OPPE managers, particularly Dennis Tirpak, objected that it was unreasonable for one EPA Office to block a peer-reviewed report by another office simply because of arguments that people might make with the information. The Policy office had the mission to warn people about the environmental impacts of climate change. After two years, Richard Laska decided that continuing to hold up the study was unlikely to make the study more accurate, and suggested that the Wetland Office simply put their concerns in the report itself, which they did in the form of Chapter 5, and the report was published in the summer of 1988.

    Chapter 1 was the official EPA version of a paper that had gradually evolved from an article in the National Wetlands Newsletter. Titus also drafted some material regarding options for allowing wetlands to migrate inland, but EPA managers decided that it would be better for this report to simply state how the impact on wetlands depends in part on human activities, given the policy sensitivity of land use. EPA management encouraged Titus to publish the policy ideas in an academic journal, so the complete version of this paper along with a policy analysis was eventually published in Greenhouse effect and coastal wetland policy: how Americans could abandon an area the size of Massachusetts at minimum cost.

    Chapter 2 was originally published in 1985, as a stand-alone study as a followup to the The Charleston case study that Kana et al. had conducted as part of EPA's original sea level rise assessment of Charleston and Galveston. Kana put forth the idea of using tide ranges to estimate elevations of coastal wetlands, which would be more precise than available elevation data.

    Chapter 3 was simply a micro-tidal version of the study in Chapter 2.

    Chapter 4 was the original effort to model the impact of sea level rise on wetlands. Although the concept was originally sold to EPA by Tom Armentano, he turned the modeling part of the project over to Richard Park, who began assembling the model that came to be known as SLAMM. This initial approach did not incorporate the tidal-elevation ideas discussed by Kana et al. in chapters 2 and 3, nor the shore protection issues discussed by Titus in chapter 1. But this first effort led EPA to provide Park with sufficient funding to develop an improved version of SLAMM that did incorporate those ideas as part of a 1989 Report to Congress.

    Chapter 5 was provided by EPA's wetlands office at the suggestion of EPA's external affairs coordinator, who wanted to ensure that the report satisfied their concerns when it was published.

    This document has been reviewed in accordance with the U.S. Environmental Protection Agency peer and administrative review policies and approved for publication. Mention of trade names or commercial products does not constitute endorsement or recommendation for use. Please send comments to James G. Titus, U.S. Environmental Protection Agency, Washington, D.C. 20460.

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