1998 Year of the Ocean Impacts of Global Climate Change 



pattern of chemical and microbiological contamination in coastal areas, and increased coastal 

 flooding. 



Some coastal ecosystems are particularly at risk, including saltwater marshes, coastal 

 wetlands, coral reefs, coral atolls, and river deltas. Other critical coastal resources, such as 

 mangroves and sea-grass beds, submerged systems including submerged aquatic vegetation , and 

 mudflats, are at risk from climate change impacts, and exacerbated by anthropogenic factors. 

 Changes in these ecosystems could have major negative effects on tourism, freshwater supplies, 

 fisheries, and biodiversity that could make coastal impacts an important economic concern. 

 These impacts would add to modifications in the functioning of coastal oceans and inland waters 

 that already have resulted from pollution, physical modification, and material inputs due to 

 human activities. Secondary impacts associated with climate change, such as inundation of waste 

 disposal sites and landfills that in turn will reintroduce toxic materials and increased siltation into 

 the environment, also pose threats to the health of coastal populations and ecosystems. 



Global sea levels have been rising since the conclusion of the last Ice Age approximately 

 15,000 years ago. During the last 100 years, sea-level rise has occurred at approximately 1-2.5 

 mm/yr. This figure represents eustatic sea level (the absolute elevation of the Earth's ocean) that 

 has been determined from tidal stations around the globe. However, there are large regional 

 variations due to: subsidence, isostatic (glacial) rebound, tectonic uplift, etc., that contribute to a 

 "relative" sea-level rise. For example, within the U.S., portions of the Gulf Coast are 

 experiencing a relative sea-level rise of 10 mm/year. Concurrently, the coast of Alaska is 

 experiencing a negative relative sea-level fall of up to 8 mm/year; i.e. sea level is receding. 

 Figure 7 illustrates the change in sea level along U.S. coasts as determined from historical tidal 

 data. If this historical rate of sea-level rise is projected to 2100, sea level would rise 10-27 cm 

 globally. A recent EPA study assessed the probability of sea level rise along various U.S. coastal 

 towns and estimated that there is a one percent change of a 120 cm rise and a 50 percent chance 

 of a 55 cm rise in sea level by the year 2100 along the New York coast. 



Rising global temperatures could further raise sea level by expanding ocean water, 

 melting alpine and other small glaciers, and perhaps eventually causing the polar ice sheets of 

 Greenland and Antarctica to melt into the oceans. The most recent IPCC assessment (1995) 

 forecasts a rise in global sea level of 5 mm/year, within a range of uncertainty of 2-9 mm/year 

 with almost all of the contribution resulting from thermal expansion and melting small glaciers. 

 The IPCC predicts low, mid, and high estimates of 20, 49, and 86 cm. This current best forecast 

 represents a rate of sea-level rise that is still about two to five times the rate experienced over the 

 last 100 years. Furthermore, even if greenhouse-gas concentrations are stabilized, model 

 projections show that sea level will continue to rise beyond the year 2100 due to lags in response 

 to climate change. Figure 8 indicates the potential impact of a 50 cm sea-level rise, or 

 approximately the mid-range IPCC estimate, in South Florida. 



The IPCC estimates are based on the effects of thermal expansion of the ocean. They do 

 not include the possible contribution that the melting of the Greenland and Antarctic ice sheets 



G-26 



