1998 Year of the Ocean Impacts of Global Climate Change 



would have on sea-level rise. While still debated and somewhat speculative, such melting would 

 provide a much greater contribution to global sea-level rise. 



Coastal land, including buildings, transportation infrastructure, and recreational and 

 agricultural areas, is vulnerable to inundation and increased erosion as a result of climate change. 

 All lowlands are threatened by a rise in sea level. Estuaries are also threatened by potential 

 hydrologic changes that could increase the range of saltwater intrusion as well as alter the 

 amount of freshwater reaching an estuary. If a one-meter rise in sea level occurs during the next 

 century, the worst-case IPCC scenario, thousands of square miles could be lost, particularly in 

 low-lying areas such as the Mississippi delta, where land is also subsiding at a rate of 

 approximately one meter per century. Table 1 indicates the estimated land loss for seven regions 

 of the United States. Storm damage is expected to also increase, particularly along the well- 

 developed and low-lying Atlantic and Gulf of Mexico coasts. 



Assessing total economic impacts from sea-level rise on coastal areas and on a national 

 scale is still somewhat speculative. Nevertheless, a recent study has quantified the present value 

 of the economic costs (protection plus abandonment) to coastal structures with a 1 -meter sea- 

 level rise as $6.4 billion between 1996 and the year 2100. However, this figure represents only 

 market-valued estimates which are derived from property-value appreciation, market adaptation, 

 and protection costs. Thus, it is a minimum cost estimate which does not include the lost service 

 value of non-market resources, such as tidal wetlands. Estimates of impact on such resources are 

 more difficult to quantify because they lie outside the traditional market and have not yet been 

 thoroughly measured. Natural systems, like a tidal wetland, can provide flood control, storm 

 protection, and waste recycling and have tremendous value when measured economically. 



Coastal erosion is already a widespread problem in the United States. For example, in 

 Oahu, Hawaii, over the past 50 years a quarter of the beaches have been lost or significantly 

 degraded due to causes that are poorly understood. Heightened storm surge could increase the 

 rate of erosion. The highest-risk areas are those with very low relief and currently experiencing 

 rapid erosion rates, such as the southeastern United States and the Gulf Coast (see Figure 9). 

 Coastal areas would also be more vulnerable to hurricanes, as well as to increased or decreased 

 freshwater and sediment flux from river systems. 



Rising sea-level will, in general, increase storm surge flooding by the level of sea-level 

 rise, making every coastal storm appear more intense. However, some areas will experience 

 dramatic changes — going from no flooding to extensive flooding. Many coastal features, such as 

 levees, seawalls, and naturally occurring sand dunes and ridge lines effectively block storm 

 surges for most storms. Whenever one of these features is overtopped by storm surge from either 

 a hurricane or an extratropical storm, the areas inland will flood. Numerical modeling has shown 

 that large amounts of water can move over such barriers, flooding over the marshland or bay 

 behind the barrier, and sweeping over mainland areas. 



G-29 



