The Effect of Rising Sea Levels on Global Coasts - Essay Example

and Number of the Teacher’s THE EFFECT OF RISING SEA LEVELS ON GLOBAL COASTS Introduction One of the most certain outcomes of green-house induced climate change is the increasing speed at which sea levels are rising in the global coasts, with many adverse impacts on the world’s coastline. Since the dawn of civilization, “the coastal zones of the world have been important to mankind” (Nicholls & Leatherman: 92, 93). Today, a large proportion of the population lives in the coastal zone, with twenty of the world’s thirty largest cities being on the coast. The resources of the coastal zone are greatly subjected to stresses by the growing population and development. Hence, the additional burden of climate change on these resources is a matter of concern. The rise in sea level is correlated with a global rise in temperature. The geographical impacts of rising sea levels include the flooding of major coastlines, changes caused to the coral reefs and marine life, the effects on wetlands, marshlands and tidal inlets, the outcomes on hurricanes and other occurrences, and changes in the chemical composition of oceans. The future effects of global warming on ice-bound polar regions may result in increasing rises in sea levels. The purpose of this paper is to determine the various geographical effects of rising sea levels on global coasts. The ways in which these will impact on mankind will be discussed, and the measures to reduce the adverse effects will be identified. Discussion Research evidence points to a discernible effect on the earth’s climate caused by greenhouse gases which emerge mainly from anthropogenic or human activities. These effects are intensifying in the 21st century with various climatic effects including a higher rate of global sea level rise (Warrick et al: 257). Wthin 30 kilometers of the coastline, 21% of the world’s population already lives and these populations are growing at twice the global average (Nicholls et al: S69). The potential impacts of sea-level rise are being assessed, in order to formulate policies and implement appropriate remedial measures. Major changes in sea level have occurred over the centuries, which is evident from eroded landforms such as cliffs, depositional features such as coral reefs, biological indicators such as organisms whose fossils indicate the position of the old shoreline, archaelogical remains such as submerged dwellings or ports, and historical documents and records (Haslett: 128). Unlike other forms of climate change, increasing rise in sea-level is already a global problem. Rising sea levels can directly submerge low-lying wetland and dryland areas, cause erosion of shores by loss of sediment, “increase the salinity of estuaries and aquifers, raise coastal water tables and exacerbate coastal flooding and storm damage” (Nicholls & Leatherman: 93). It is estimated that over the last century, sea level has risen all over the world, by 1.8 + or – 0.1 mm/ year (Douglas: 6981). The global rise in temperature causes the thermal expansion of sea water and the melting of land-based ice mainly glaciers and ice sheets. Even small increases in sea levels have global impacts over the long term. It is estimated that over 70% of the world’s sandy coasts are presently diminishing due to erosion. Worldwide receding of shoreline is predominantly attributed to rising sea levels. Quantitative estimates of future sea level rise are as low as 0.1 meters to as high as 3.7 meters by the year 2100 (Warrick & Oerlemans: 257). Flooding of Major Coastlines by Rising Sea Levels According to research and analysis conducted by Nicholls et al (p.S69), the number of people affected by storm induced floods in an average year would be five times higher due to sea level rise by the 2080s. The areas most prone to floods are those with high concentrations of low-lying populated deltas such as in southern Mediterranean, Africa, and most particularly South and South-east Asia. However, greatest relative increase in flood risk would be experienced by the Caribbean, the Indian Ocean Islands and the Pacific Ocean small islands (Nicholls et al: S85). By the 2080s, up to 22% of the world’s coastal wetlands may be lost due to sea level rise. “When combined with other losses due to direct human action, up to 70% of the world’s coastal wetlands could be lost by the 2080s. The maximum losses due to rising sea levels will be incurred by the Mediterranean and Baltic and to a lesser extent by the Atlantic coast of Central and North America and the smaller islands of the Caribbean. Thus, a relatively small global rise of only 37/ 38 centimeters in sea level can produce significant adverse impacts, if no measures are taken against it. The decline in coastal wetlands caused by flooding are not the same globally, and some regions are more affected than others (Nicholls et al, S85). The results of vulnerability assessments reveal that “a number of developing countries are particularly vulnerable to the effects of sea-level rise” (Nicholls & Leatherman: 92). The measures used for assessment were national overviews and selected case studies undertaken in Brazil, Egypt, Bangladesh, India, Malaysia and China. Detailed national assessments using aerial videotape-assisted vulnerability analysis were carried out in Senegal, Argentina, Nigeria, Uruguay and Venezuela. Sea level rises of 0.2, 0.5 and 1.0 meter by the year 2100 were taken into consideration, using a 1 meter rise as a standard measure for all cases. Those areas which have the potential to lose their use due to rise in sea level, were termed at risk. Losses due to a 1 meter rise in sea level would be $12 billion for the Netherlands, $74 billion for Japan, and $200 to $475 billion for the United States (Nicholls & Leatherman: 93). Fig.1. Shoreline Retreat Due to Rise in Sea Level (Titus et al: p.7). Figure 1. The Bruun Rule depicting shoreline retreat due to inundation caused by a rise in sea level is shown in a and b. (a). Initial condition; (b) immediate inundation when sea level rises; (c) consequent erosion as a result of sea level rise. A three-foot rise in sea level implies that the offshore bottom must also rise by 3 feet. Beach nourishment supplies the sand required to raise the bottom (X’). Otherwise, from the upper part of the beach, waves will erode the required sand (X), as depicted in (c). In the United States “most of the wetlands and lowlands are found along the Gulf Coast and the Atlantic coast south of the central part of New Jersey, although there is also a large low area around San Francisco Bay” (Titus et al: 176). Similarly, the areas vulnerable to erosion and flooding are also situated mainly in the southeast, and potential salinity problems are prevalent throughout the coast. Major port cities with low areas include Boston, New York, Charleston, Miami, and New Orleans which is about two metres below sea level, and parts of Texas City, San Jose and Long Beach California are about one meter below sea level. The recreational barrier islands and spits of the Atlantic and Gulf Coasts are some of the most important vulnerable areas. Normally, the oceanfront block of an island ranges from two to four meters above high tide, while the bay side is less than a meter above high water. “Thus, even a one-meter rise in sea level would threaten much of this valuable land with inundation” (Titus et al: 176-177). The Changes Caused to Coral Reefs Coral reefs and related organisms such as calcareous algae have built extensive reefs in tropical areas, more prevalent in the western parts of the oceans within a zone extending 30 degrees North and 30 degrees South of the Equator. Fringing reefs built out from the coastline, barrier reefs built offshore parallel to the coastline, atolls surrounding a marine lagoon, and outlying patch reefs constitute the various types of coral reefs. These have been built by coral polyps, small marine organisms (Eisma: 50). The effects of a rising sea level on coral reefs depend on the ability of corals to grow on the submerging reef flats. Living corals which are few and scattered on reefs if killed, are not replaced quickly. Many corals are already under various types of stress caused by ecological factors as the result of human activities. Moreover, some of the less vigorous may fail to revive, so that the reefs become permanently submerged with rise in sea levels. Since a slowly rising sea level supports the revival of coral growth on reef flats, “it is possible that coral communities will maintain their level relative to the rising sea” (Eisma: 51). Coral growth is generally 0.4 to 7.0 millimeters per year. Sometimes growing coral may fail to keep up with the rising sea, or may be underwater and lifeless. A rapid rise in sea level helps to maintain upward growth of coral reefs, while a slow down of sea level rise may help others to grow to the surface. The responsiveness to sea level changes is seen in the coral reefs in Western Australia (Bird: 382). Impact on Marine Life A rise in sea level would result in saltwater reaching further inland and upstream in rivers, bays, wetlands, and aquifers which would be harmful to some aquatic plants and animals. It would also pose a threat to human use of water. Higher levels of salinity prove to be a contributing factor for reduction of oyster harvests in Delaware and Chesapeake Bays, and for transforming Cypress swamps in Louisiana to form open lakes (Titus et al: 178). Coastal marine habitats are vulnerable to changes in sea level. Because of decreasing availability of light due to increasing water depth, subtidal marine plants and tropical corals will be impacted, affecting distribution and abundance. For example, a 50 centimeter rise in sea level could result in 30% to 40% reduction in the growth of Zostera marina which is a sea grass wide spread in the northern hemisphere. In several areas, the receding shoreline with shift of plants and animals will be impeded by coastal development. Sea level rise also changes the range of local tides, depending on the coastal topography. The area in which acroalgae and fauna are located in the intertidal and subtidal, are based on an increase or decrease of tidal range. Rising sea levels can cause the depletion of plant communities on the wetlands (Gibson et al: 446-447). Mangroves normally occur on low-profile, low-energy coastlines, ecologically in saline intertidal locations. They are particularly susceptible to rapid changes in sea levels. If sediment accretion rates in mangroves are equal to or more than the sea level rise, then mangroves will persist. Bird species are also threatened by rising sea levels. Low-lying coastal areas are valuable breeding sites for nesting birds, and are impacted by erosion and flooding. Some examples are the kingfisher and spangled drongo which nest on the low-lying islands of the Torres Strait; and the noddy that nests in mangroves. Further, beaches that breed marine turtles are affected by sea level rise, for example on the island of Bonaire in the Caribbean (Gibson et al: 447). Effect on Chemical Composition of Oceans Normal sea level changes produce coast line changes from 100 to 1000 kilometers. Changes in ice sheet volume impact sea level. Sea level changes have a direct impact on the composition of the ocean, which have a direct impact on ocean-atmosphere chemical composition. These composition changes can cause substantial change in global sea climate by changing the greenhouse effect (NRC: 186). The exchange of heat, moisture and momentum between the earth’s atmosphere and the underlying surface affect every aspect of the earth’s climate. Changes in the surface energy balance are determined by are determined by changes in surface albedo and surface wetness. A rise of sea level will increase the area covered by ocean water which has a much lower albedo and a much higher wetness than the land. A change in global albedo by 0.01 will produce about 1 degree Centigrade change in surface temperature. This would cause a rise or fall of about 100 meters or more in the sea level. This would lead to marked changes in evaporation and subsequently in precipitation though not necessarily in the same area. This will also significantly change the summer temperatures because of the much larger thermal inertia of the ocean as compared to the land. A marked redistribution of surface areas of momentum exchange between land, ocean and atmosphere would affect the atmospheric circulatory systems. Enhanced evaporation in partially isolated basins caused by sea-level change can produce water masses of different density as compared to the main ocean (NRC: 27). With rise in sea levels, hurricane frequency, intensity and distribution have also increased. Based on “high levels of runoff and sediment delivery, the turbidity and salinity of the water may be changed” (Goudie: 250). The Changes in Wetlands, Marshlands and Tidal Inlets Coastal wetlands which comprise of saltmarshes, mangroves and intertidal areas could experience extensive losses due to rising sea levels. These areas are highly productive and have important uses (Bijlsma et al: 289). It is expected that a significant rate of wetland losses will continue after the 2080s, if sea levels continue to rise. Losses of wetlands will have adverse outcomes on many sectors and operations, including food production such as loss of nursery areas for fisheries, nature conservation, flood and storm protection such as preventing storm surges penetrating further inland, waste assimilation, treatment and nutrient cycling functions, and provision of habitats for wildlife. Thus wetland losses have a high human cost (Nicholls et al: S84). Wetland areas are declining every year at the rate of 1% of the global coastal wetland stock; for which direct reclamation is being implemented. Even without climate change, significant losses are expected to continue, which will be accelerated by rise in sea level. With rising level of the sea, the surface level of a coastal wetland rises due to vertical accretion caused by increased sediment and organic matter deposits. However, “if the rate of vertical accretion is less than the rate of sea-level rise, the coastal wetland steadily loses elevation relative to sea level” (Nicholls et al: S85, S75). It is the land in deltas which are most at risk due to rise in sea levels, as they would be subject to inundation. Countries with extensive delta areas used for farming, with agricultural populations, are particularly vulnerable. These are Egypt, Bangladesh and China. For a rise in sea level of 1 meter, 12% to 15% of the agricultural land in Egypt and over six million people will be at risk. In Bangladesh, land that provides 16% of the national rice production which is inhabited by thirteen million people will be at risk. The Sunderbans, the second largest mangrove swamp in the world, and one of the last refuges of the Bengal tiger could be completely eliminated. In China predominantly in the four main coastal plains, major cities such as Shanghai and Tianjin, 72 million people and also tens of thousands of square kilometers of agricultural land will be at risk. High value land along many sandy coasts are also at risk of erosion. Globally, extensive reductions of coastal wetlands will possibly be undertaken, but may result in adverse outcomes on coastal resources such as fisheries (Nicholls & Leatherman: 92). Reinforcement with sand on tourist beaches as a protection measure, and other options such as land raising and sea-wall emplacement would be significantly expensive undertakings. In the case of Uruguay and Senegal, based on gross investment in 1990, protection costs are greater than for Nigeria, Venezuela, and Argentina. Vulnerability to sea-level rise could be greatly reduced by building setbacks. Future major coastal development should be regulated within integrated coastal zone management plans, with the main aim of reducing vulnerability to future sea-level rise. Increasingly larger populations would be living beneath sea level, and could face disastrous consequences if coastal defenses failed. All protection measures should be designed taking this risk into consideration. In the case of deltas, new techniques such as sediment management may prove to be useful. However, there are limits to human adaptation. Even in developed countries, it is difficult to counter the estimated loss of coastal wetlands (Nicholls & Leatherman: 92). A research study was undertaken to determine whether the geomorphology of a tidal inlet which is made up of the coastal inlet and associated tidal basin is able to maintain equilibrium while there is rise in sea level. Sediment has to be imported into the system on a permanent basis. A new state of dynamic morphological equilibrium is reached if the rate of sediment import matches the rate of sea level rise. “If the actual import rate is less than this, the system’s morphological state will deviate increasingly from its equilibrium and finally degenerate” (Van Goor: 211). The results from this study comply with the available fragmentary geological data which suggest that the former tidal inlets in the western region of the Netherlands were drowned under the influence of a sea-level rise of 80 cm to a few metres per century. Increase in Hurricanes and other Occurrences There is found to be a link between sea-level rise and other manifestations of climate change, such as changing storm intensity and frequency of hurricanes (Nicholls & Leatherman: 92). Storm surges can cause floods. In Fig.2. the different zones which are at risk of flooding, that exist on low lying coasts are seen. These risk zones will move upwards with rise in sea level, thus increasing the number of people vulnerable to flooding; and increasing the flood risk of the population within the flood plain. Fig. 2. The Coastal Flood Plains Including Different Storm Surge Levels and Corresponding Risk Zones (Nicholls et al: S72) By calculating the changes in flood risk, three factors which are associated with human exposure to such flooding are derived. These are: people in the hazard zone (PHZ): the number of people living below the 1000-year storm surge elevation (H1000 in Fig.1.0); the average annual people flooded by storm surge including the influence of sea defences; people to respond (PTR) to flooding by storm surge which occur more than once a year, hence they strengthen flood protection, migrate, and respond in a precautionary manner to the threat (Bijlsma et al: 289). Impact of Global Warming on the Ice-Bound Polar Regions The greenhouse effect may raise sea levels by different amounts in different regions. Global warming and the removal of water from the world’s ice sheets would move the earth’s center of gravity away from Greenland and Antarctica, resulting in redistribution of the ocean’s water towards the new center of gravity. This would effect a sea level rise by less than 10% along the coast of the United States. However, at Cape Horn and along the coast of Iceland, the sea level could actually drop.Local sea level may also be impacted by climate change, by changing winds, atmospheric pressure, and ocean currents (Titus et al: 175). With increase in global temperatures, precipitation would increase over Greenland resulting in higher accumulation of ice. For every 1 degree rise in global temperature, precipitation would increase by 4%. However, this accumulation will occur in the interior of Greenland only, as most of the outlet glaciers around the Greenland coast receded greatly during the twentieth century. It is not certain how Greenland icesheet has contributed to sea level, and it appears probable that it is unrelated to thermal expansion and melting of non-polar valley glaciers (Haslett: 142). In a manner similar to the Greenland icesheet, the Antarctic icesheet also accumulates ice through an increase in precipitation brought about by global warming. However, unlike Greenland, the Antarctic ice sheet has a positive balance, accumulating more ice than it loses through melting, resulting in growth of the ice sheet. Its contribution to sea level is finely balanced because the West Antarctic Ice Sheet is grounded below sea level so that it may be very sensitive to sea level rise which lifts the ice sheet off the sea floor. This would decrease the bottom stresses of the ice sheet, allowing it to flow faster and thin more rapidly. With increase in icebergs breaking off, there will be increased rise in sea level (Haslett: 142). According to Singer & Avery (p.48), 1 degree Celsius of warming would create only a small change in global sea levels. The melting of Greenland’s icesheet would increase sea level only by 0.3 to 0.77 mm. per year; while Antarctica will subtract 0.2 to 0.7 mm. per year with addition to its ice cap due to increased precipitation. Policy Implications It is crucial that proactive planning, formulation of policies and implementation of measures be undertaken against the potential impacts of sea-level rise. An important area for policy is greenhouse gas emission. Mitigation policies would help to slow down, but will not be able to stop the expected rise in sea level which will occur even with stabilization of greenhouse effect in the next few years. This mitigation policy is known as “commitment to sea level rise” (Warrick & Oerlemans: 258). Analysis using several impact models such as food, water and coastal flooding reveal that the positive outcomes from mitigation policies will be available only after the 2050s. Hence, adaptation to global sea level rise will be a crucial requirement during the current century. Proactive measures to deal with yearly floods which cause heavy human tolls and loss of coastal wetlands, are required. Reducing flood impacts through policies include strategies for planned retreat such as zoning vulnerable areas as unsuitable for development; accommodation built at elevated levels; and protection by means of flood walls which are regularly renewed and upgraded (Bijlsma et al: 289). Preventive Measures Against the Impact of Rising Sea Levels Fig.3. Responses to Sea Level Rise for Developed Barrier Islands Legend: -------------------- Original Sea Level; – – – – – – – – Original Beach Profile (Titus et al: 179) Figure 3 illustrates four possible responses by which sea level rise can be countered by barrier islands: no protection, engineering a landward retreat, raising the island in place and building a levee. From a case study of Long Beach Island, New Jersey, it was found that a combination of all the protection options would still be less expensive as compared to the value of the land that was threatened by inundation. Although raising islands would work out more expensive than constructing levees and seawalls, the former alternative is preferable because constructing levees and seawalls would cause the loss of beaches and waterfront views, and retreat would not be possible for islands with high-rises, and would also be more expensive (Titus et al: 179). Some methods of preventing the impact of rising sea levels are: “erecting walls to hold back the sea; allowing the sea to advance and adapting to it: and raising the land” (Titus et al: 178). The slow rise in sea level over the last thousand years and the regions with rapidly sinking land provide historical examples of all these measures. The Dutch have used dikes and windmills to prevent inundation from the North Sea. Since structures and land were lost to erosion, many cities have been rebuilt such as the town of Dunwich, England which rebuilt its church seven times in the last seven centuries. More recently, Galveston, Texas has used fill to raise land elevations; and sand is regularly pumped from offshore to counteract beach erosion. All the three above measures have been implemented by Venice, allowing the sea to extend into the canals, while raising the level of low lands and erecting storm protection barriers. In the United States, low-lying coastal cities would be protected with “bulkheads, levees, and pumping systems, while in sparsely developed areas shorelines would retreat naturally” (Titus et al: 178). Conclusion This paper has highlighted the effect of rising sea levels on global coasts, focusing on the geographical impacts on major coastlines, coral reefs, marine life, chemical composition of oceans, wetlands and marshlands, increase in hurricanes and other natural occurrences, potential worst case scenarios of ice thaws in the polar regions, and their effects on mankind. Possible preventive measures have also been outlined. It is crucial to formulate flexible coastal zone policies that can be adapted to changing conditions. With rising global sea levels, most sandy shorelines are receding, “coastal wetlands are being lost, and coastal populations continue to grow rapidly” (Nicholls & Leatherman: 93). Policies to counteract accelerated sea level rise need to be implemented urgently. However, most undertakings are based on long-term planning for producing effective results, such as land-use planning. The range of possible responses to sea level rise have to be considered by all, and preventive action taken, keeping future generations’ interests in mind. The core issue behind sea level rise being global warming, this feature needs to be countered with adequate measures based on governmental policies, and for which every individual can contribute in their own way. Works Cited Bijlsma, L., Ehler, C.N., Klein, R.J.T., Kulshrestha, S.M., McLean, R.F., Mimura, N., Mimura, N., Nicholls, R.J., Nurse, L.A. , et al. Coastal zones and small islands. In R.T. Watson, M.C. Zinyowera & R.H. Moss. (Eds.). Impacts, adaptations and mitigation of climate change: Scientific-technical analysis. Cambridge: Cambridge University Press. (1996): pp. 289-324. Bird, Eric. Coastal geomorphology. New Jersey: John Wiley & Sons. 2008. Douglas, Bruce C. Global sea level rise. 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