Coastal Areas

-- An overview prepared by Susanne Moser, Ph.D. (Union of Concerned Scientists) --

Climate and changes in it – regardless of their cause – matter to people, communities and businesses. Global warming is likely to bring many changes to the nation. The United States as a whole is in a strong economic position to adapt to many of these changes, but adaptation is often expensive not always possible or successful, and even when ultimately successful, during transitions ecosystems, communities, and individuals could suffer. Moreover, national impact summaries disguise local dislocations and disruptions to the ways we live, work and recreate. Climate change adds a serious stress to our already threatened resources and treasured places. Overall impact statements also mask significant opportunities. To minimize the negative changes and make the most of the positive changes we need to take a close look at how climate change will affect each region. How will coastal areas experience the effects of global warming? And how can we respond?

Key Findings

Global warming adds a significant stress to coastal environments already experiencing intense development and population pressures. The National Assessment discusses the potential impacts of climate change on sea level, the shoreline and resulting threats to properties, infrastructure and coastal industries, and on coastal and marine ecosystems.

Sea-level rise, shoreline erosion and flooding
Over the last century, global sea level has risen on average 4-10 inches. The rate of sea-level rise may already have accelerated over the last 100 years. According to the scenarios used in the assessment, the rate of sea-level rise could as much as double over the course of this century. Regional climate regimes and local land movement (subsidence or uplift) will determine local amounts of sea-level rise (SLR). If global warming continues unchecked, major urban areas built near sea level along the Eastern seaboard including New York City, Boston, Washington, DC, and Miami will be at risk with an expected SLR of 18-20 inches above current levels by 2100. Low-lying infrastructure in these areas including buildings, roads, power lines, airports, train and subway systems are all at risk to increased flooding. Recreational areas enjoyed by millions, including the beaches of New Jersey, Long Island, the Hamptons, North Carolina and Florida’s Gold Coast will be at risk to accelerated beach erosion and loss. Where land is sinking rapidly, as along parts of the Gulf coast including New Orleans and Galveston, SLR may be significantly faster; where land is being lifted up, as along parts of the Pacific coast and Alaska, SLR will be slower or not experienced at all. While the projected sea-level rise itself seems modest, its effects are heightened during storms because the area flooded due to storm surge and higher wave heights is greatly expanded. One study reported in the National Assessment shows how flooding of the level that currently occurs only during the most severe storms (e.g., a once-per-100-years event) could occur much more frequently, as often as every few years. Virginia Burkett, Chief of the Forest Ecology Branch at the National Wetlands Research Center in Lafayette, LA thus cautions to not think of erosion worsened by sea-level rise “simply as a gradual process. Sea-level rise increases erosion rates and property damages occurring during storms by increasing storm surge and wave height.”

Sea-level rise in addition to human development of the coastal zone could lead to widespread wetlands loss threatening important habitat for shorebirds, plants, and nursery areas for fish, as well as valuable ecosystem services. Already, according to Burkett, because of the combined stresses of relative SLR and other human alterations of the coastal environment, “the wetlands and barrier islands that protected South Louisiana have eroded about 30% since 1900.” In Florida, sabal palms are thought to be dying in coastal lowlands because of rising sea level. Salt-water intrusion into underground water resources is a problem in many coastal states (e.g., CA, MA, NC, SC and FL) threatening water quality for residential and industrial users. Says Denise Reed, geomorphologist at the University of New Orleans, “where ecosystems are already heavily altered and stressed by human impacts, sea-level rise could be the straw that breaks the camel’s back.”

Flooded community along Bayou Lafourche in coastal Louisiana after landfall of Hurricane Juan in 1985. (Source: Virginia Burkett, USGS, National Wetlands Research Center)

Coastal storms
Climate models provide no clear conclusions yet as to potential changes in the frequency or intensity of coastal storms. The number of tropical and extratropical storms has varied over past decades, in part related to phenomena like El Niño, shifting ocean currents over the Atlantic, and rainfall patterns in tropical areas. Since Hurricane Andrew in 1992, the US has entered a phase with more frequent tropical storms and hurricanes. However, the assessment concludes, even if storm intensity and frequency remain the same in the future, with the increased population and development in coastal areas, and increased flooding due to higher sea levels, property losses will continue to increase.

Winter storms in the mid-latitude can also produce high damages in coastal areas, as evidenced during the 1997-98 El Niño winter when California, Oregon and Washington experienced record rainfall, flooding, and incidences of cliff erosion and mudslides. Some climate models show El Niños increasing in frequency and strength, which would increase these kinds of coastal hazards.

Homes on cliffs of Pacifica, CA

Coastal agriculture, coral reefs and marine ecosystem health
Runoff into coastal waters may increase or decrease, depending on location and the complex interaction of various climatic changes. In many cases, water quality is likely to change and become unsuitable for certain uses, either because of the increased influx of sediments and pollutants with higher runoff, or because of decreased flushing and higher salinity levels with reduced stream flows. Increased salinity could threaten water quality for residential users as well as certain types of agriculture, like rice, which are extremely sensitive to salinity increases and could not be sustained in areas where saltwater intrudes into the groundwater. Combined with higher water temperatures, coastal areas are likely to see an increased risk of low-oxygen conditions threatening fish stocks and other marine organisms (as e.g., in the Gulf of Mexico, Chesapeake Bay, and Long Island Sound); toxic algal blooms leading to shellfish mortality (as e.g., in the estuaries of North Carolina); bacterial problems along beaches posing a health threat to beach users, thus negatively affecting coastal tourism (as experienced in California in 1998); and species shifts to cooler waters adding to the difficulties recreational and commercial fisheries already face (documented already along the Pacific Northwest and the Atlantic coasts). Coral reef communities, the “canaries” of the tropical oceans, form another marine ecosystem known to be under chronic stress, largely from human activities. Warmer ocean temperatures, higher carbon dioxide and nutrient concentrations, higher sea levels and sediment loads, and possibly more frequent destructive storms could add climate-induced stresses that may threaten their survival. Excessively high ocean temperatures as a result of the El Niño in 1998 have already led to bleaching of coral reefs around the world.

Adapting to the impacts of global warming

Coastal areas are likely to bear a significant burden from the impacts of climate change. Climate scientists agree that further climate change may be inevitable and will therefore require adaptation, although most scientists also think that the pace of climate change can be slowed by substantially reducing greenhouse gas emissions. This would give governments, businesses, and ecosystems around the world more time to respond and adapt to climate change as well as reducing the overall severity of climate change-related impacts, thereby buying "insurance" for an uncertain future. Another way to buy insurance now is to incorporate climate change into all long-term decisions about natural resources, thereby providing greater resilience.

Impacts on coastal and marine resources, valuable ecosystems and treasured places are the result of local human and environmental stresses and global climate changes. Given the long-term nature of climate change and sea-level rise, and the scientific uncertainties about them, there is a temptation to postpone any long-term planning and decisions. However, today’s decisions and in-decisions affect tomorrow’s options. Thus, the most effective management options in the context of climate change are those that reduce local stresses to the greatest extent possible to compensate for large-scale changes that cannot single-handedly be affected locally. For example,

• Many barrier island systems in the US have survived thousands of years of changing sea level. To give them a fighting change in the next century we must work with natural processes and restore pathways of sediment movement in the coastal zone, for example by removing jetties or installing sand-bypassing systems.


• Many coastal wetlands are currently so stressed from human activities that additional sea-level rise will result in submergence. In marshes that are naturally self-sustaining, restoring natural hydrologic function, for example replacing culverts with bridges, closing canals that cut across natural drainage, or removing migration barriers, is a vital step in helping them keep pace with sea-level rise.


• Coral reefs are among the most deteriorated marine ecosystems, with natural stress factors, like climate variability and storm impacts, and growing human impacts producing a complex set of threats. Reducing marine pollution, over-fishing, and recreational over-use are ways to control the local human impacts on this valuable ecosystem.


• Tighter development controls like hazard mitigation or ecosystem restoration requirements, setbacks, zoning, and conservation easements in the coastal zone can reduce vulnerability to hazards, water quality deterioration, urban sprawl, wetland loss and other local stresses on the coastal region.

Where do we go from here?

The assessment of regional and sectoral impacts from climate variability and change, especially when based on global climate models, is hampered by the inherent complexity of the climatic, ecological and societal systems involved. Our scientific understanding of these systems and their interactions has much progressed in recent years and decades, but uncertainties persist. Thus, scientific research and assessments of the possible impacts of climate variability and change on coastal regions and marine resources must continue to more specifically and reliably inform coastal managers. Progress in regional climate modeling, regional sea-level rise and local shoreline change projections, predictions of changes in climate variability, and a better understanding of the complex interactions between various climatic and environmental systems that will undergo change as the climate warms will provide a sturdier base for coastal management.

In the meantime, the national discourse about climate change begun through this National Assessment must be continued among scientists and stakeholders at all levels of government, in non-governmental organizations, and in the private sector. State and local initiatives to address sea-level rise should be shared, discussed, and pilot tested more broadly. And those most likely to be affected by the impacts of climate change must be made aware of the risks climate change poses to their communities, treasured resources, unique environments, and livelihoods.

Additional Information

For more detailed information on the impacts of global warming on coastal areas and marine resources, several experts are available to answer your questions:

Dr. Virginia Burkett, Ph.D., National Wetlands Research Center, Lafayette, LA
 Tel.: (337) 266-8636
Dr. Denise Reed, Ph.D., University of New Orleans, LA
 Tel.: (504) 280-7395

Contact UCS Assistant Press Secretary Paul Fain at 202-332-0900 with further questions or to set up interviews with a UCS staff scientist.