Greenhouse effect, sea level rise, and coastal wetlands

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