1998 Year of the Ocean Impacts of Global Climate Change 



Climate change also has the potential to significantly affect coastal biological diversity. It 

 could cause changes in the population sizes and distributions of species, alter the species 

 composition and geographical extent of habitats and ecosystems, and increase the rate of species 

 extinction. Fragile systems such as coral reefs are highly susceptible to temperature increases. 

 Short-term increases in water temperatures on the order of only 1-2°C, combined with other 

 environmental stresses (such as pollution or siltation from human activities), can cause 

 "bleaching," leading to significant reef destruction. Reefs in many parts of the world, including 

 the United States, have undergone episodes of bleaching, particularly in the 1980s. Sustained 

 increases of 3-4°C above long-term average seasonal maximums can cause significant coral 

 mortality. Biologists suggest that full regeneration of these coral communities could require 

 several centuries. 



Fisheries in estuaries and the coastal ocean are also vulnerable to changes in water 

 temperature and freshwater inflow. The loss of coastal wetlands has already been implicated in 

 the decline of shrimp harvests in Louisiana, and would also likely reduce yields of crab and 

 menhaden. Projections of general circulation models suggest that freshwater discharge from the 

 Mississippi River to the coastal ocean will increase 20 percent if atmospheric carbon dioxide 

 concentrations doubles. This is likely to affect water column stability, surface productivity, and 

 global oxygen cycling in the northern Gulf of Mexico, which is already suffering from persistent 

 hypoxia. In the open ocean, increased temperatures could result in a shifting of the geographical 

 distribution of certain species. Decreasing freshwater flow, when combined with rising sea level 

 could result in the encroachment of saltwater species into typically freshwater habitats. For 

 example, in estuaries, decreased freshwater inflow could result in increased salinity and, in turn, 

 a replacement of some freshwater species by saltwater species. 



Management Issues and Strategies 



Management strategies in coastal areas can be divided into three categories: 



(1) Accommodate. Vulnerable areas continue to be occupied, accepting the greater 

 degree of effects, e.g., flooding, saltwater intrusion, and erosion; advanced coastal 

 management used to avoid the worst impacts; improved early warning of catastrophic 

 events; and building codes modified to strengthen structures 



(2) Protect. Vulnerable areas, particularly population centers, high-value economic 

 activities, and critical natural resources, are defended by sea walls, bulklieads, 

 saltwater intrusion barriers; other infrastructure investments are made; and "soft" 

 structural options such as periodic beach re-nourishment, landfill, dune maintenance 

 or restoration, and wetlands creation are carried out 



(3) Retreat. Existing structures and infrastructure in vulnerable areas are abandoned, 

 inhabitants are resettled, government subsidies are withdrawn, and new development 

 is required to be set back specific distances from the shore, as appropriate. 



G-34 



