Risks and Effects of Sea Level Rise on Coastal Peoples and Ecosystems in the Gulf of Mexico Region
Final Report
May 11, 2007
Ecological Risk Assessment
Chris Beal
Jessica DeBiasio
Peter Spartos
Sarah Wilkins
Executive Summary
As a result of global climate change, scientists are seeing a rise of sea levels around the world. Although there has been some debate concerning the degree of rise over the next decade, the impacts will be significant. Warming temperatures are melting polar ice caps, adding large amounts of water to the ocean which in turn raises ocean temperatures causing thermal expansion. In addition, subsidence and groundwater depletion cause the shoreline to sink creating isolated sea level rise conditions. All of these contribute to coastal migration of populations as the water rises and shores move further inland. The transition of coastal forests and other ecosystems to higher elevations is often hindered by shoreline development, effectively isolating these ecosystems and preventing migration. As sea level rises, human populations will be displaced, adversely affecting tourism industries and local economies; loss of seaports, difficulties in distribution of public resources and the risks to human health will also increase. The use of tools such as the coastal vulnerability indices can help identify areas most at risk to sea level rise and provide the basis for responses and management options to help abate the effects of rising seas.
Table of Contents
Problem Statement
Background
Figure 1: Changes in Temperature, Sea Level, and Northern Hemisphere Snow Cover.
Table 1: Observed rate of sea-level rise and estimated contributions from different sources.
Focal Region
Goal/Purpose Statement
Objectives
Approach
Findings
Coastal Vulnerability Index
Table 2. Coastal Vulnerability Index for the Gulf of Mexico region
Figure 2. Percentage of the U.S. Gulf of Mexico Coast shoreline in each risk category
Figure 3. Map of coastal vulnerability index and risk rankings…………………
Ecological Impacts
Forest Decline and Saltwater Intrusion
Wetland Loss
Flooding
Coastal Erosion and Barrier Island Loss
Socioeconomic and Cultural Impacts
Commercial Fisheries
Agriculture
Oil, Gas, and Chemical Industries
Tourism and Entertainment, Port Transfer and Shipping
Public Resources, Water, and Land
Displacement of Coastal Peoples and Health Risks
Management Opportunities
Conclusions and Recommendations
Works Cited
Problem Statement
Sea level rise across the next century will have adverse effects on human populations and ecosystems in low-lying coastal areas of the Gulf of Mexico.
Background
For years, global climate change has been the focus of debate and speculation between leading scientists and politicians. The most recent edition of the International Panel on Climate Change (IPCC), released in April 2007, has cleared up much of this doubt. Scientists have determined with 95% certainty that human activities are a primary cause of this warming trend and the associated effects.Global sea levels have risen at an average observed rate of 1.8mm per year from 1961 to 2003 and at a rate of 3.1 mm per year from 1993 to 2003.[1]The total sea-level rise for the 20th century is estimated to be 170 mm(Alley et al, 2007).
Prior to the Industrial Revolution, anthropogenic contributions of greenhouse gases (carbon dioxide: CO2, methane: CH4, and nitrous oxide: N2O) to the atmosphere were low compared to current levels(Alley et al, 2007). The dramatic increase in CO2has been linked to intensified fossil fuel use. In the 1990’s, average annual CO2 emissions were estimated at 22.0-25.0 GtCO2 per year. This grew to 25.3-27.5 GtCO2 per year in 2000-2005 and emissions continue to rise. The 4th IPCC concluded that the increase in CH4 is very likely due to human industries, namely agriculture and fossil fuel use, while N2O increases are primarily caused by agricultural activities. As shown in figure 1, global average temperature and sea level have increased dramatically since 1950 (Alley et al, 2007).
Figure 1: Changes in Temperature, Sea Level, and Northern Hemisphere Snow Cover.
Observed changes in (a) global average surface temperature; (b) global average sea level rise from tide gauge (blue) and satellite (red) data and (c) Northern Hemisphere snow cover for March-April. All changes are relative to corresponding averages for the period 1961-1990. Smoothed curves represent decadal averaged values while circles show yearly values. The shaded areas are the uncertainty intervals estimated from a comprehensive analysis of known uncertainties (a and b) and from the time series (c)(Alley et al, 2007).
The effects of global warming are becoming increasingly evident. The changes in air and ocean temperatures along with decreases in annual snow and ice cover have contributed to a slow but steady rise in sea-level. Direct contributors to sea level rise and their annual contribution in millimeters are shown in Table 1. The largest observed source of sea level rise is the melting of glaciers and ice caps (Figure 1).
Table 1: Observed rate of sea-level rise and estimated contributions from different sources(Alley et al, 2007).
Models have produced various scenarios supporting the connection between a continued rise in global temperatures and sea level. The IPCC-SRES models low and high scenarios give ranges for global sea level rise of 0.18-0.38 meters with a 1.8ºC increase in global temperature and 0.26-0.59 meters with a 4.0ºC increase (Alley et al, 2007).
FocalRegion
The GulfCoast region is one of the nation’s largest ecological systems and is a significant contributor to the nation’s economy. Sea-level rise poses great risks to these important entities. States at risk include Alabama, Florida, Louisiana, Mississippi, and Texas, as well as a reach of the Mexican shoreline. Many variables play into sea-level rise and all must be considered in order to comprehend the magnitude and scope of this dynamic issue(Ning et al. 2003).
Gulf States have been adversely affected as a result of this rise. For the ten year period from 1985 to 1995, states in the southeastern U.S. lost over 32,000 acres of coastal marshlands as a result of natural subsidence, human development, erosion and sea-level rise(Ning et al. 2003).
Goal/Purpose Statement
This report focuses on characterizing the risk of impacts, as a result of sea level rise, on ecosystems, cultures/societies, and economies in low-lying areas of the Gulf of Mexico region. In addition, this report explores the management options available to deal with these risks.
Objectives
This project is designed to characterize the effects of sea level rise. A risk characterization clarifies the relationship between stressors, effects, and ecological entities in order to guide management (GERA, 1998).
This report reviews various papers that explore the following:
- Direct impact of sea-level rise on ecosystems and the impact of relative sea-level and tidal effects.
- Explore economic impacts on industry, and ecosystem services.
- Human health impacts and displacement of coastal communities.
Approach
Methodologies include literature collection and thereview of scientific journals and various reports, government documents and the most recent publication on climate change by the IPCC.
Findings
The first section of the findings describes the ecological impacts associated with sea level rise in the Gulf of Mexico region. The second portion of the findings describes the secondary impacts on human populations including, but not limited to, the listed socioeconomic and cultural effects. It is important to remember that none of the impacts listed act in isolation. Each is interconnected to others and complex in nature. Included throughout this section are management opportunities provided in the reports reviewed in this document.
Coastal Vulnerability Index
Table 2. Coastal Vulnerability Index for the Gulf of Mexico region (Thieler and Hammar-Klose, 2000).
The Coastal Vulnerability Index (CVI), shown in Table 2, allows researchers to quantitatively evaluate the vulnerability of coastal areas based on characteristics of geomorphology. Coastal slope, rate of sea level rise, rate of accretion and erosion, average tidal range, and average wave height are used to rank areas in respect to the risk of impact. Out of 8,058 km of the Gulf of Mexico coastline surveyed using the CVI, 3,867.84 km are at very high vulnerability, 1,047.54 km are at high vulnerability, 2,981.46 km are at moderate vulnerability, and 644.64 km are at low vulnerability (Table 2)(Thieler and Hammar-Klose, 2000).
Figure 2. Percentage of the U.S. Gulf of Mexico Coast shoreline in each risk category(Thieler and Hammar-Klose, 2000).
The majority of the Gulf coast is dominated by barrier islands, lagoons, marshes and deltas which have a high risk ranking. In addition to the geomorphology of the area, the entire coast is micro-tidal, meaning that only slight variations in sea level occur between low and high tide events which yield a high risk ranking as well (Figure 2).
Figure 3. Map of coastal vulnerability index and risk rankings(Thieler and Hammar-Klose, 2000).
CVI are necessary for long term coastal planning. At present, development is taking place without proper consideration of the costs associated with shoreline retreat (i.e. erosion, increased flooding, and storm damage). Entire communities and their residents have the potential to be displaced, and many high end real-estate ventures are at risk of damage due to sea level rise. Sea level rise is eminent as are the effects that will ensue as it continues, however the severity of these effects are still not clearly understood(Thieler and Hammar-Klose, 2000).
Ecological Impacts
Sea level rise will pose great risks to ecosystems and their ecological integrity. The ecological impacts include: forest decline and saltwater intrusion, wetland loss, flooding, coastal erosion and barrier island loss. Management opportunities are included at the end of thereport, highlighting potential steps that managers can take in order to protect vulnerable areas.
Forest Decline and Saltwater Intrusion
Sea-level rise along the GulfCoast and for some distance inland has caused major stress on coastal forests. As a result of sea-level rise, salt water intrusion and the duration and timing of flooding can significantly alter the productivity of coastal ecosystems. Freshwater swamps are being stressed by saltwater intrusion while bottomland hardwoods are also being killed by manipulations in the timing and duration of floods events(Ning et al, 2003). In a study conducted by McKee and Mendelssohn in 1989, salinity stress was shown to lower plant productivity (Day et al, 1995).
Williams et al. (1999)explores this relationship by studying coastal forests that are affected by tidal flooding. They wanted to describe the mechanism by which sea-level rise initiates forest retreat. The authors found that stands of sabal palms that were subjected to more frequent flooding had more standing dead palms and stunted palms than similar sites with less flooding. These sites containedhighly saline groundwater,while groundwater under healthy palm stands had lower salinities. The study suggests that the relationship between saltwater intrusion and tree stands is significantsince regeneration often fails several decades before mature canopy turnover. Future studies therefore, should focus on the rate of tree regeneration, not just forest canopy health, in order to account for sea-level rise (Williams et al, 1999).
The encroachment of ocean on coastal forests has led to changes in species composition, wetland boundaries, and the complete loss of some terrestrial ecosystems. This has made the region more susceptible to destructive insect pests. It is predicted that longleaf and slash pine forests could expand northward and replace some of the loblolly and shortleaf pine forests located throughout many of the Gulf States. Along the GulfCoast in Florida, potential diebacks of entire forests are possible. Elevated sea levels will prevent lenticel function and oxygen uptake.Mangroves are also predicted to suffer large diebacks as a result of rising sea levels(Ning et al, 2003).
Wetland Loss
Coastal wetlands are among some of the most productive ecosystems in the world and are home to numerous aquatic and terrestrial species. Coastal wetlands also act as an important buffer between the ocean and dry land. In some areas, such as Louisiana, wetlands can actually suppress storm surges and protect the vulnerable inner coast. With decreased accretion rates due to channelization of waterways, the excessive use of levees and embankments, and increased subsidence, existing wetlands are diminishing and their ability to abate storm surges successfully is being lost(Kennish 2001).
Eighty percent of national coastal wetland loss has occurred in Louisiana alone. Forty-one percent of the nation’s wetlands occur in Louisiana. The transformation of coastal wetlands to open water accounts for nearly 60% of wetland loss, the majority of which has been caused by erosion. In all, 2,500 km² of coastal wetlands have been lost in Louisiana over the past 45 years (Kennish, 2001).
The reduction of sediment supplies and high rate of sea level rise along the Chenier Coast of Texas has created major erosion problems. Up to 70% of the Texas coast has experienced erosion rates of approximately 10m/yr (Kennish, 2001).
Flooding
Rising sea levels reduce the drainage of rivers and streams, increasing flood events (Day et al, 1995). When marshes are flooded frequently soils become inundated with salt and as a result, plants become physiologically stressed. If soils do not accumulate the adequate quantities of organic and inorganic matter to compensate for rising sea-levels and subsidence, then marshes will become open water (Ning et al, 2003).
Coastal Erosion and BarrierIsland Loss
The coastal erosion of barrier islands and beaches places immense pressure on ecosystems and people living in coastal communities. Larger storm surges and rising water levels will lead to the loss of barrier islands and wetlands that protect vulnerable coastal ecosystems and human settlements. The low-lying deltas of Mississippi and Louisiana are particularly vulnerable to the effects of increased erosion and storm damage threats (Ning et al, 2003).
Socioeconomic and Cultural Impacts
Rising sea levels will have major impacts on commercial fisheries, agriculture, oil, gas and chemical industries, tourism and entertainment, port transfer and shipping, public utilities, andthe displacement of human populations and associated health risks. These impacts will in turn affect socioeconomic and cultural institutionsof the GulfCoast states. A great deal of uncertainty remains when determining the full range of risks involved.
Commercial Fisheries
As mentioned earlier in this report, sea level rise has resulted in the deterioration of coastal wetlands throughout the GulfCoast region. Associated impacts on fisheries are expected due to the loss of valuable wetland habitat. Estuaries and coastal marshlands are unique ecosystems that act as nurseries for juvenile fishes and are obligate habitat for commercially valuable species. Many fishing industries depend on wetlands exclusively to provide valuable harvests. The loss of wetlands and coastal areas due to erosion, subsidence, and sea level rise will impede on the ability of fisherpeople to harvest successfully(Ning et al, 2003).
Agriculture
Salinization of irrigation waters willlead to the degradation of agricultural soils, as well as drastic decreases in crop yields (Ning et al, 2003). Overall warming of the globe is predicted to be beneficial to agricultural yields, but only within a 1-3°C increase in local average temperature. Any increase in temperature above this range is predicted to cause a decrease in production. For lower latitudes such as the Gulf Region, crop production is predicted to decrease with even a small increase (1-2°C) in local average temperature (Adger et al, 2007).
Oil, Gas, and Chemical Industries
In 2003, eighteen percent of United States oil was produced along the Louisiana coast. The risk of land loss due to subsidence and rising sea levels threatens 30,000 oil wells and related infrastructure (NOAA Magazine, 2003). The removal of oil from these areas also exacerbates sea level rise, by increasing subsidence and increasing the vulnerability of coastal communities and habitat to strong storm surges. These companies must weigh the costs of protecting the coastline with the costs of relocating their operations. If they choose to stay, the implications of coastal protection failure and resulting property loss must also be considered. Dramatic increases in the cost of insurance associated in areas with a high risk of sea level rise have also occurred along the coast. Continued increases in premiums may eventually lead to the withdrawal of risk coverage in these vulnerable areas, especially from private insurers (Adger et al, 2007). Big industry and oil companies are not likely to change their business practices, especially when most have seen large increases in profits over these last few years[2](McLean, 2007).
The chemical industry is primarily affected indirectly by sea level rise through the impacts on raw material supplies from the oil and gas industries (Ning et al, 2007).
Tourism and Entertainment, Port Transfer and Shipping
The loss of valued ecosystems for recreation and tourism could be potentially devastating, especially for communities and regions that depend nearly exclusively on tourism for local economic support. The pristine beaches and colorful coral that draw thousands of people each year are now becoming eroded beaches and bleached coral. Along with vital ecosystem services, coral reefs attract visitors from all over the United States each year. A study conducted in the South Pacific concluded that in very extreme cases up to 75% of tourism revenue could be lost, by and large due to the loss in coral reefs (DukeUniversity, 2001).
Access to ports may also be impaired by changing river flow rates, increased sedimentation and the need for dredging, while shipping traffic could be affected by severe storms and changing seabed landscapes(Ning et al, 2003).
Public Resources, Water, and Land