Greenhouse Effect and Sea Level Rise: The Cost of Holding Back the Sea
|JAMES G.TITUS, US Environmental Protection Agency (Washington, DC 20460)|
|RICHARD A. PARK, Indiana University (Bloomington, IN 47405)|
|STEPHEN P. LEATHERMAN, University of Maryland (College Park, MD 20742)|
|J. RICHARD WEGGEL, Drexel University (Philadelphia, PA 19104)|
|MICHAEL S. GREENE, The Bruce Company (Washington, DC 20024)|
|PAUL W. MAUSEL, Indiana State University (Terre Haute, IN 47809)|
|SCOTT BROWN, JCA Associates (Mt. Laurel, NJ 08054)|
|CARY GAUNT, Science Applications International Corp. (Mclean, VA 22102)|
|MANJIT TREHAN, Indiana University and Purdue University (Indianapolis, IN 46202)|
|GARY YOHE, Wesleyan University (Middletown, CT 06457)|
Greenhouse Effect and Sea Level Rise: The Cost of Holding Back the Sea (PDF, 30 pp., 906 KB) was originally published in Coastal Management (1991), Volume 19, 171-204. The report's Abstract, Introduction and Summary and Conclusions sections are available below. For faster viewing, Cost of Holding Back the Sea is also available as an html document.
For additional reports focused on the implications of rising sea level, go to More Sea Level Rise Reports.
Previous studies suggest that the expected global warming from the greenhouse effect could raise sea level 50 to 200 centimeters (2 to 7 feet) in the next century. This article presents the first nationwide assessment of the primary impacts of such a rise on the United States: (1) the cost of protecting ocean resort communities by pumping sand onto beaches and gradually raising barrier islands in place; (2) the cost of protecting developed areas along sheltered waters through the use of levees (dikes) and bulkheads; and (3) the loss of coastal wetlands and undeveloped lowlands. The total cost for a one meter rise would be $270-475 billion, ignoring future development.
We estimate that if no measures are taken to hold back the sea, a one meter rise in sea level would inundate 14,000 square miles, with wet and dry land each accounting for about half the loss. The 1500 square kilometers (600-700 square miles) of densely developed coastal lowlands could be protected for approximately one to two thousand dollars per year for a typical coastal lot. Given high coastal property values, holding back the sea would probably be cost-effective.
The environmental consequences of doing so, however, may not be acceptable. Although the most common engineering solution for protecting the ocean coast--pumping sand--would allow us to keep our beaches, levees and bulkheads along sheltered waters would gradually eliminate most of the nation's wetland shorelines. To ensure the long-term survival of coastal wetlands, federal and state environmental agencies should begin to lay the groundwork for a gradual abandonment of coastal lowlands as sea level rises.
At the turn of the century, scientific opinion regarding the practical implications of the greenhouse effect was sharply divided. Since the 1860s, people had known that by absorbing outgoing infrared radiation, atmospheric CO2 keeps the Earth warmer than it would otherwise be (Tyndall, 1863). Svante Arrhenius (1896), who coined the term "greenhouse effect," pointed out that the combustion of fossil fuels might increase the level of CO2 in the atmosphere, and thereby warm the Earth several degrees. Because the 19th century had experienced a cooling trend, however, others speculated that the oceans and plant life might gradually reduce CO2 levels and cause an ice age (Barrel et al., 1919).
Throughout the first half of the 20th century, scientists generally recognized the significance of the greenhouse effect, but most thought that humanity was unlikely to substantially alter its impact on climate. The oceans contain 50 times as much CO2 as the atmosphere, and physical laws governing the relationship between the concentrations of CO2 in the oceans and in the atmosphere seemed to suggest that this ratio would remain fixed, implying that only 2 percent of the CO2 released by human activities would remain in the atmosphere. This complacency, however, was shattered in 1957 when Revelle and Seuss (1957) demonstrated that the oceans could not absorb CO2 as rapidly as humanity was releasing it: "Human beings are now carrying out a large-scale geophysical experiment." Only then were monitoring stations set up to measure worldwide trends in atmospheric concentrations. By the mid 1960s, it was clear that Revelle and Seuss had been correct (President's Science Advisory Committee, 1965).
In the last decade, climatologists have reached a consensus that a doubling of CO2 would warm the Earth 1.5-4.5°C (3-8°F), which could leave our planet warmer than it has ever been during the last two million years (National Academy of Sciences, 1979). Moreover, humanity is increasing the concentrations of other gases whose combined greenhouse effect could be as great as that due to CO2 alone, including methane, chlorofluorocarbons, nitrous oxide, and sulfur dioxide (Ramanathan et al., 1985). Even with the recent agreement to curtail the use of CFCs, global temperatures could rise as much as 5°C (9°F) in the next century (Smith and Tirpak, 1988). Global warming would alter precipitation patterns, change the frequency of droughts and severe storms, and raise the level of the oceans.
This article presents the first attempt to quantify the nationwide impacts of an accelerated rise in sea level. The study was undertaken in response to a request from the U.S. Congress to the Environmental Protection Agency, and had to be completed in twelve months with a budget of $300,000. With these constraints, we were only able to focus on the loss of dry and wet land and the cost of holding back the sea.
Because our focus was on aspects that can be most readily estimated on a nationwide basis, we have disregarded impacts who importance is limited to a few areas--in particular the threat to coastal water supplies from saltwater intrusion and the unique situation in Louisiana. We hope that this study will motivate others to improve on the methods presented here and to start quantifying other impacts of global warming.
We estimate the shoreline retreat from a one meter rise in sea level would cost the United States 270 to 475 billion dollars. Like all cost estimates involving unprecedented activities, our estimates ignore the impacts we could not readily quantify and those we can not foresee. But policymakers are accustomed to "soft" estimates, and we see no reason to believe that our estimates are any worse than the norm.
Table 9 summarizes our calculations. Thirty-six thousand square kilometers (fourteen thousand square miles) of land could be lost from a one meter rise, with wet and dry land each accounting for about half the loss. For a few hundred billion dollars, fifteen hundred square kilometers (six to seven hundred square miles) of currently developed land could be protected, but the loss of coastal wetlands would be that much greater.
|Table 9. Summary of Nationwide Results|
|(billions of dollars unless otherwise stated)|
|Baseline||50 cm||100 cm||200 cm|
|If No Shores Are Protected|
|Dryland Lost (sq mi)||N.C.||3,315-7,311||5,123-10,330||8,191-15,394|
|Wetlands Lost (%)||N.C.||17-43||26-66||29-76|
|If Developed Areas Are Protected|
|Dryland Lost (sq mi)||1470-4686||2,200-6,100||4,100-9,200||6,400-13,500|
|Wetlands Lost (%)||9-25||20-45||29-69||33-80|
|Value of Lost Land||16-47||52-130||86-212||112-297|
|Land for Dikes||0||9-33||14-48||22-74|
|Cost of Coastal Defense||4||55-123||143-305||402-645|
|Open Coast: Sand||4||15-81||27-146||59-284|
|Open Coast: Elevate Structures||0||29-36||62-170||257-316|
|Sheltered Shores: Dike Construct||0||5-13||11-33||30-101|
|Total Cost - Inundation and Erosion||20-51||128-232||270-475||576-880|
|If All Shores Are Protected|
|Wetlands Lost (%)||N.C.||38-61||50-82||66-90|
|N.C. = Not Calculated.|
Our estimates are optimistically low because we assume that it will only be necessary to protect areas that are developed today, that is, about 15 percent of U.S. coastal low lands. If development continues and (1) we protect those areas as well, the economic impact could be far greater because more dikes would be necessary and wetland loss would be greater. If development continues but (2) we eventually abandon those areas, the wetland loss will be the same as assumed in this article, but there could be a tremendous loss of homes, offices, and infrastructures as the abandonment takes place. But (3) prohibiting coastal development would also have costly impacts on the economy, which we would have to add. Thus, this article is a severe underestimate of the nation-wide cost of sea level rise unless we implement a means of abandoning low-lying areas at little or no cost.
At the national level, protecting developed coastal areas appears to be cost-effective. The cumulative figure would be spread over one hundred years; even at the end of the century, the annual cost of protection on barrier islands would be about $2,000 for a quarter-acre lot--hardly a welcome prospect for coastal property owners but nevertheless one well worth bearing in order to maintain the property. The cost of protecting developed mainland areas would be only about one-tenth as great.
The fact that protecting property is cost-effective does not necessarily imply that it would be in the interest of society to do so. We must also consider the loss of natural shorelines and coastal wetlands that would result. Our results suggest that up to a point, the objectives of protecting wetlands and coastal property may be compatible. Abandoning developed areas would increase the area of surviving wetlands by only 5 to 10 percent--but at great cost. By contrast, limiting coastal protection to areas that are already developed (and allowing currently-undeveloped areas to flood) would increase the area of surviving coastal wetlands by 40 to 100 percent, depending on how much the sea rises.
Moreover, estimates in areal losses understate the differences in environmental impacts for the various policy options. Although a substantial loss would occur even if developed areas were abandoned, most of today's wetland shorelines would still have wetlands; the strip would simply be narrower. By contrast, protecting all mainland shorelines could leave our coastal wetlands confined to a small number of isolated reserves, a situation that humanity has already imposed on many terrestrial species.
Our results are consistent with the hypothesis of a 1987 study by the National Academy of Engineering that shore protection will be cost-effective for most developed areas (Dean et al., 1987). From the perspective of civil engineers, that study concluded that little action is necessary today because shore protection structures can be erected rapidly compared with the rate of sea level rise. However, the speed with which communities could build these structures is small comfort to the birds and fish whose habitat would be destroyed by doing so.
Sea level rise is an urgent issue for coastal environmental planners for the very reason that it lacks urgency for some directors of public works. If state and local governments fail to develop plans to protect the coastal environment as the sea rises, the public will almost certainly call upon engineers to protect their homes in the years to come.
Greenhouse Effect and Sea Level Rise: The Cost of Holding Back the Sea (PDF, 30 pp., 906 KB) was originally published in Coastal Management (1991), Volume 19, 171-204.