Potential Interactions with Coastal Areas and Marine Resources

The United States has over 95,000 miles of coastline and over 3.4 million square miles of ocean within its territorial waters. These areas provide a wide range of goods and services to the U.S. economy. Approximately 53 percent of the U.S. population lives on the 17 percent of land in counties that are adjacent to or relatively near the coast. Over recent decades, populations in these coastal counties have been growing more rapidly than elsewhere in the country. As a result of this population growth and increased wealth, demands on coastal and marine resources for both leisure activities and economic benefits are rapidly intensifying, while at the same time exposure to coastal hazards is increasing.

Coastal and marine environments are intrinsically linked to the prevailing climate in many ways. Heat given off by the oceans warms the land during the winter, and ocean waters help to keep coastal regions cooler during the summer. Moisture evaporated from the oceans is the ultimate source of precipitation, and the runoff of precipitation carries nutrients, pollutants, and other materials from the land to the ocean. Sea level exerts a major influence on the coastal zone, shaping barrier islands and pushing salt water up estuaries and into aquifers. For example, cycles of beach and cliff erosion along the Pacific Coast have been linked to the natural sequence of El Niño events that alter storm tracks and temporarily raise average sea levels by several inches in this region (NCAG 2000). During the 1982 -- 83 and 1997 -- 98 El Niño events, erosion damage was widespread along the Pacific coastline.

Climate change will affect interactions among conditions on the land and sea and in the atmosphere. Warming is likely to alter coastal weather and could affect the intensity, frequency, and extent of severe storms. Melting of glaciers and ice sheets and thermal expansion of ocean waters will cause sea level to rise, which is likely to intensify erosion and endanger coastal structures. Rising sea level and higher temperatures are also likely to affect the ecology of estuaries and coastal wetlands. Higher temperatures coupled with increasing CO₂ concentrations are likely to severely stress coral reefs, and the changing temperature patterns are likely to cause fisheries to relocate and alter fish migration patterns. While quantifying these consequences is difficult, indications of the types of outcomes that are possible have emerged from U.S. assessments (NCAG 2000).

Effects on Sea Level

Global sea level rose by 10 -- 20 cm (about 4 -- 8 inches) during the 20th century, which was significantly more than the rate of rise that was typical over the last few thousand years. Even in the absence of a change in Atlantic storminess, the deeper inundation that has resulted from recent storms has exacerbated flooding and has led to damage to fixed coastal structures from storms that were previously inconsequential.

Looking to the future, climate models project that global warming will increase sea level by 9 -- 88 cm (4 -- 35 inches) during the 21st century, with mid-range values more likely than the very high or very low estimates (IPCC 2001d). Because of the long time constants involved in ocean warming and glacier and ice sheet melting, further sea level rise is likely for several centuries, even after achieving significant limitations in emissions of CO₂ and other greenhouse gases. However, these global changes are only one factor in what determines sea level change at any particular coastal location. For example, along the Mid-Atlantic coast, where land levels are subsiding, relative sea level rise will be somewhat greater; conversely, in New England, where land levels are rising, relative sea level rise will be somewhat less.

Not surprisingly, an increased rate of global sea level rise is likely to have the most dramatic impacts in regions where subsidence and erosion problems already exist. Estuaries, wetlands, and shorelines along the Atlantic and Gulf coasts are especially vulnerable. Impacts on fixed structures will intensify, even in the absence of an increase in storminess. However, because the slope of these areas is so gentle, even a small rise in sea level can produce a large inland shift of the shoreline. The rise will be particularly important if the frequency or intensity of storm surges or hurricanes increases.

Increases in the frequency or intensity of El Niño events would also likely exacerbate the impacts of long-term sea level rise. Coastal erosion increases the threats to coastal development, transportation infrastructure, tourism, fresh-water aquifers, fisheries (many of which are already stressed by human activities), and coastal ecosystems. Coastal cities and towns, especially those in storm-prone regions, such as the Southeast, are particularly vulnerable. Intensive residential and commercial development in these regions is placing more and more lives and property at risk (Figure 6-10).

Effects on Estuaries

Climate change and sea level rise could present significant threats to valuable, productive coastal ecosystems. For example, estuaries filter and purify water and provide critical nursery and habitat functions for many commercially important fish and shellfish populations. Because the temperature increase is projected to be greater in the winter than in the summer, a narrowing of the annual water temperature range of many estuaries is likely. This, in turn, is likely to cause a shift in species' ranges and to increase the vulnerability of some estuaries to invasive species (NCAG 2000).

Changes in runoff are also likely to adversely affect estuaries. Unless new agricultural technologies allow reduced use of fertilizers, higher rates of runoff are likely to deliver greater amounts of nutrients such as nitrogen and phosphorus to estuaries, while simultaneously increasing the stratification between fresh-water runoff and marine waters. Such conditions would be likely to increase the potential for algal blooms that deplete the water of oxygen. These conditions would also increase stresses on sea grasses, fish, shellfish, and other organisms living in lakes, streams, and oceans (NCAG 2000, and regional assessment reports). In addition, decreased runoff is likely to reduce flushing, decrease the size of estuarine nursery zones, and increase the range of estuarine habitat susceptible to predators and pathogens of shellfish.

Effects on Wetlands

Coastal wetlands (marshes and mangroves) are highly productive ecosystems, particularly because they are strongly linked to the productivity of fisheries. Dramatic losses of coastal wetlands have occurred along the Gulf Coast due to subsidence, alterations in flow and sediment load caused by dams and levees, dredge and fill activities, and sea level rise. Louisiana alone has been losing land at rates of about 68 -- 104 square kilometers (24 -- 40 square miles) per year for the last 40 years, accounting for as much as 80 percent of the total U.S. coastal wetland loss.

In general, coastal wetlands will survive if soil buildup equals the rate of relative sea level rise or if they are able to migrate inland (although this migration necessarily displaces other ecosystems or land uses). However, if soil accumulation does not keep pace with sea level rise, or if bluffs, coastal development, or shoreline protective structures (such as dikes, sea walls, and jetties) block wetland migration, wetlands may be excessively inundated and, thus, lost. The projected increase in the current rate of sea level rise is very likely to exacerbate the nationwide rate of loss of existing coastal wetlands, although the extent of impacts will vary among regions, and some impacts may be moderated by the inland formation of new wetlands.

Effects on Coral Reefs

The demise or continued deterioration of reefs could have profound implications for the United States. Coral reefs play a major role in the environment and economies of Florida and Hawaii as well as in most U.S. territories in the Caribbean and Pacific. They support fisheries, recreation, and tourism and protect coastal areas. In addition, coral reefs are one of the largest global storehouses of marine biodiversity, sheltering one-quarter of all marine life and containing extensive untapped genetic resources.

The last few years have seen unprecedented declines in the health of coral reefs. The 1998 El Niño was associated with record sea-surface temperatures and associated coral bleaching (which occurs when coral expel the algae that live within them and that are necessary to their survival). In some regions, as much as 70 percent of the coral may have died in a single season. There has also been an upsurge in the variety, incidence, and virulence of coral diseases in recent years, with major die-offs in Florida and much of the Caribbean region (NCAG 2000).

Other factors that are likely to be contributing to the decline of coral reefs include increased sediment deposition, sewage and agricultural runoff, excessive harvesting of fish, and damage from ships and tourists. In addition to the potential influences of further global warming, increasing atmospheric CO₂ concentrations are likely to decrease the calcification rates of the reef-building corals, resulting in weaker skeletons, reduced growth rates, and increased vulnerability to wave-induced damage. Model results suggest that these effects would likely be most severe at the current margins of coral reef distribution, meaning that it is unlikely coral reefs will be able to spread northward to reach cooler waters. While steps can be taken to reduce the impacts of some types of stress on coral reefs (e.g., by creating Marine Protected Areas, as called for in Executive Order 13158, and constructing artificial reefs to provide habitat for threatened species), damage to coral reefs from climate change and the increasing CO₂ concentration may be moderated to some extent only by significantly reducing other stresses.

Effects on Marine Fisheries

Based on studies summarized in the coastal sector assessment, recreational and commercial fishing has contributed approximately $40 billion a year to the U.S. economy, with total marine landings averaging about 4.5 million metric tons over the last decade. Climate change is very likely to substantially alter the distribution and abundance of major fish stocks, many of which are a shared international resource.

Along the Pacific Coast, impacts to fisheries related to the El Niño -- Southern Oscillation illustrate how climate directly affects marine fisheries on short time scales. For example, elevated sea-surface temperatures associated with the 1997 -- 98 El Niño had a tremendous impact on the distribution and abundance of market squid. Although California's largest fishery by volume, squid landings fell to less than 1,000 metric tons in the 1997 -- 98 season, down from a record-breaking 110,000 metric tons in the 1996 -- 97 season. Many other unusual events occurred during this same El Niño as a result of elevated sea-surface temperatures. Examples include widespread deaths of California sea lion pups, catches of warm-water marlin in the usually frigid waters off Washington State, and poor salmon returns in Bristol Bay, Alaska.

The changes in fish stocks resulting from climate change are also likely to have important implications for marine populations and ecosystems. Changes over the long term that will affect all nations are likely to include poleward shifts in distribution of marine populations, and changes in the timing, locations, and, perhaps, viability of migration paths and nesting and feeding areas for marine mammals and other species.

With changing ocean temperatures and conditions, shifts in the distribution of commercially important species are likely, affecting U.S. and international fisheries. For example, model projections suggest that several species of Pacific salmon are likely to have reduced distribution and productivity, while species that thrive in warmer waters, such as Pacific sardine and Atlantic menhaden, are likely to show an increased distribution. Presuming that the rate of climate change is gradual, the many efforts being made to better manage the world's fisheries might promote adaptation to climate change, along with helping to relieve the many other pressures on these resources.

Potential Adaptation Options for Coastal Regions

Because climate variability is currently a dominant factor in shaping coastal and marine systems, projecting the specific effects of climate change over the next few decades and evaluating the potential effectiveness of possible response options is particularly challenging. Effects will surely vary greatly among the diverse coastal regions of the nation. Human-induced disturbances also influence coastal and marine systems, often reducing the ability of systems to adapt, so that systems that might ordinarily be capable of responding to variability and change are less able to do so. In this context, climate change is likely to add to the cumulative impact of both natural and human-caused stresses on ecological systems and resources. As a result, strategies for adapting to the potential consequences of long-term climate change in the overall context of coastal development and management are only beginning to be considered (NCAG 2000).

However, as further plans are made for development of land in the coastal zone, it is especially urgent for governing bodies at all levels to begin to consider the potential changes in the coastal climate and sea level. For example, the U.S. Geological Survey is expanding its gathering and assembly of relevant coastal information, and the U.S. Environmental Protection Agency's Sea Level Rise project is dedicated to motivating adaptation to rising sea level. This project has assessed the probability and has identified and mapped vulnerable low-elevation coastal zones. In addition, cost-effective strategies and land-use planning approaches involving landward migration of wetlands, levee building, incorporation of sea level rise in beach conservation plans, engineered landward retreats, and sea walls have all been developed.

Several states have already included sea level rise in their planning, and some have already implemented adaptation activities. For example, in New Jersey, where relative sea level is rising approximately one inch (2.5 cm) every six years, $15 million is now set aside each year for shore protection, and the state discourages construction that would later require sea walls. In addition, Maine, Rhode Island, South

Carolina, and Massachusetts have implemented various forms of "rolling easement" policies to ensure that wetlands and beaches can migrate inland as sea level rises, and that coastal landowners and conservation agencies can purchase the required easements. Other states have modified regulations on, for example, beach preservation, land reclamation, and inward migration of wetlands and beaches. Wider consideration of potential consequences is especially important, however, because some regulatory programs continue to permit structures that may block the inland shift of wetlands and beaches, and in some locations shoreline movement is precluded due to the high degree of coastal development.

To safeguard people and better manage resources along the coast, NOAA provides weather forecasts and remotely sensed environmental data to federal, state, and local governments, coastal resource managers and scientists, and the public. As part of its mandate and responsibilities to administer the National Flood Insurance Program, the Federal Emergency Management Agency (FEMA) prepares Flood Insurance Rate Maps that identify and delineate areas subject to severe (1 percent annual chance) floods. FEMA also maps coastal flood hazard areas as a separate flood hazard category in recognition of the additional risk associated with wave action. In addition, FEMA is working with many coastal cities to encourage steps to reduce their vulnerability to storms and floods, including purchasing vulnerable properties.

University and state programs are also underway across the country. This is particularly important because most coastal planning in the United States is the responsibility of state and local governments, with the federal government interacting with these efforts through the development of coastal zone management plans.