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Strategies for Adaption to Sea Level Rise

Strategies for Adaption to Sea Level Rise (PDF, 147 pp., 4.4 MB) was originally published November 1990 by the Intergovernmental Panel on Climate Change, Response Strategies Working Group.

Executive Summary

Reasons for Concern

Global climate change may raise sea level as much as one metre over the next century and, in some areas, increase the frequency and severity of storms. Hundreds of thousands of square kilometres of coastal wetlands and other lowlands could be inundated. Beaches could retreat as much as a few hundred metres and protective structures may be breached. Flooding would threaten lives, agriculture, livestock, buildings and infrastructures. Salt water would advance landward into aquifers and up estuaries, threatening water supplies, ecosystems and agriculture in some areas.

Some nations are particularly vulnerable. Eight to ten million people live within one metre of high tide in each of the unprotected river deltas of Bangladesh, Egypt and Vietnam. Half a million people live in archipelagos and coral atoll nations that lie almost entirely within three metres of sea level, such as the Maldives, the Marshall Islands, Tuvalu, Kiribati and Tokelau. Other archipelagos and island nations in the Pacific, Indian Ocean and Caribbean could lose much of their beaches and arable lands, which would cause severe economic and social disruption.

Even in nations that are not, on the whole, particularly vulnerable to sea level rise, some areas could be seriously threatened. Examples include Sydney, Shanghai, coastal Louisiana and other areas economically dependent on fisheries or sensitive to changes in estuarine habitats.

As a result of present population growth and development, coastal areas worldwide are under increasing stress. In addition, increased exploitation of non-renewable resources is degrading the functions and values of coastal zones in many parts of the world. Consequently, populated coastal areas are becoming more and more vulnerable to sea level rise and other impacts of climate change. Even a small rise in sea level could have serious adverse effects.

The Coastal Zone Management Subgroup has examined the physical and institutional strategies for adapting to the potential consequences of global climate change.

Particular attention was focused on sea level rise, where most research on impacts has been conducted. The Subgroup has also reviewed the various responses and has recommended actions to reduce vulnerability to sea level rise and other impacts of climate change.

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The responses required to protect human life and property fall broadly into three categories: retreat, accommodation and protection.

Retreat involves no effort to protect the land from the sea. The coastal zone is abandoned and ecosystems shift landward. This choice can be motivated by excessive economic or environmental impacts of protection. In the extreme case, an entire area may be abandoned.

Accommodation implies that people continue to use the land at risk but do not attempt to prevent the land from being flooded. This option includes erecting emergency flood shelters, elevating buildings on piles, converting agriculture to fish farming, or growing flood or salt tolerant crops.

Protection involves hard structures such as sea walls and dikes, as well as soft solutions such as dunes and vegetation, to protect the land from the sea so that existing land uses can continue.

The appropriate mechanism for implimentation depends on the particular response. Assuming that land for settlement is available, retreat can be implemented through anticipatory land use regulations, building codes, or economic incentives. Accommodation may evolve without governmental action, but could be assisted by strengthening flood preparation and flood insurance programmes. Protection can be implemented by the authorities currently responsible for water resources and coastal protection.

Improving scientific and public understanding of the problem is also a critical component of any response strategy. The highest priorities for basic research are better projections of changes in the rate of sea level rise, precipitation and the frequency and intensity of storms. Equally important, but more often overlooked, is the need for applied research to determine which options are warranted, given current information. Finally, the available information on coastal land elevation is poor. Maps for most nations only show contours of five metres or greater, making it difficult to determine the areas and resources vulnerable to impacts of a one metre rise in sea level. Except for a few countries, there are no reliable data from which to determine how many people and how much development are at risk. There are many uncertainties and they increase as we look further into the future.

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Environmental Implications

Two thirds of the world's fish catch and many marine species, depend on coastal wetlands for their survival. Without human interference, (the retreat option), ecosystems could migrate landward as sea level rises and thus could remain largely intact, although the total area of wetlands would decline. Under the protection option, a much larger proportion of these ecosystems would be lost, especially if hard structures block their landward migration.

Along marine coasts hard structures can have a greater impact than soft solutions. Hard structures influence banks, channels, beach profiles, sediment deposits and morphology of the coastal zone.

Protective structures should be designed, as much as possible, to avoid adverse environmental impacts. Artificial reefs can create new habitats for marine species and dams can mitigate saltwater intrusion, though sometimes at the cost of adverse environmental impacts elsewhere. Soft structures such as beach nourishment retain natural shorelines, but the necessary sand mining can disrupt habitats.

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Economic Implications

No response strategy can completely eliminate the economic impacts of climate change. In the retreat option, coastal landowners and communities would suffer from loss of property, resettlement costs and the costs of rebuilding infrastructure. Under accommodation, there would be changing property values, increasing damage from storms and costs for modifying infrastructure. Under the protection option, nations and communities would face the costs for the necessary structures. The structures would protect economic development, but could adversely affect economic interests that depend on recreation and fisheries.

Appendix D of this report shows that if sea level rises by one metre, about 360,000 kilometres of coastal defences would be required at a total cost of US$500 billion over the next 100 years. (This sum only reflects the marginal or added costs and is not discounted). This value does not include costs necessary to meet present coastal defence needs. The estimate does not include the value of the unprotected dry land or ecosystems that would be lost, nor does it consider the costs of responding to saltwater intrusion or the impacts of increased storm frequency. The overall cost will therefore be considerably higher. Although some nations could bear all or part of these costs, other nations, including many small island states, could not.

To ensure that coastal development is sustainable, decisions on response strategies should be based on long term as well as short term costs and benefits.

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Social Implications

Under the retreat option, resettlement could create major problems. Resettled people are not always well received. They often face language problems, racial and religious discrimination and difficulties in obtaining employment. Even when they feel welcome, the disruption of families, friendships and traditions can be stressful.

Although the impacts of accommodation and protection would be less, they may still be important. The loss of traditional environments which normally sustain economies and cultures and provide for recreational needs could disrupt family life and create social instability. Regardless of the response eventually chosen, community participation in the decision making process is the best way to ensure that these implications are recognized.

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Legal and Institutional Implications

Existing institutions and legal frameworks may be inadequate to implement a response. Issues such as compensation for use of private property and liability for failure of coastal protection structures require national adjudication. For some options, such as resettlement (retreat option) and structures that block sediments (protection option), there are transboundary implications that must be addressed on a regional basis. International action may be required through existing conventions if inundation of land results in disputes over national borders and maritime boundaries, such as exclusive economic zones or archipelagic waters. New authorities may be required, both to implement options and to manage them over long periods of time in the face of pressures for development. National coastal management plans and other new laws and institutions are needed to plan, implement and maintain the necessary adaptive options.

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Scientists and officials from some 70 nations have expressed their views on the implications of sea level rise and other coastal impacts of global climate change at Coastal Zone Management Subgroup workshops in Miami and Perth. They indicated that in several noteworthy cases, the impacts could be disastrous; that in a few cases impacts would be trivial; but that for most coastal nations, at least for the foreseeable future, the impacts of sea level rise would be serious but manageable if appropriate actions are taken.

It is urgent for coastal nations to begin the process of adapting to sea level rise not because there is an impending catastrophe, but because there are opportunities to avoid adverse impacts by acting now, opportunities that may be lost if the process is delayed. This is also consistent with good coastal zone management practice irrespective of whether climate change occurs or not. Accordingly, the following actions are appropriate:

National Coastal Planning

1. By the year 2000, coastal nations should implement comprehensive coastal zone management plans. These plans should deal with both sea level rise and other impacts of global climate change. They should ensure that risks to populations are minimized, while recognizing the need to protect and maintain important coastal ecosystems.

2.Coastal areas at risk should be identified. National efforts should be undertaken to (a) identify functions and resources at risk from a one metre rise in sea level and (b) assess the implications of adaptive response measures on them. Improved mapping will be vital for completing this task.

3. Nations should ensure that coastal development does not increase vulnerability to sea level rise. Structural measures to prepare for sea level rise may not yet be warranted. Nevertheless, the design and location of coastal infrastructure and coastal defences should include consideration of sea level rise and other impacts of climate change. It is sometimes less expensive to incorporate these factors into the initial design of a structure than to rebuild it later. Actions in particular need of review include river levees and dams, conversions of mangroves and other wetlands for agriculture and human habitation, harvesting of coral and increased settlement in low lying areas.

4. Emergency preparedness and coastal zone response mechanisms need to be reviewed and strengthened. Efforts should be undertaken. to develop emergency preparedness plans for reducing vulnerability to coastal storms, through better evacuation planning and the development of coastal defense mechanisms that recognize the impact of sea level rise.

International Cooperation

5. A continuing international focus on the impacts of sea level rise needs to be maintained. Existing international organizations should be augmented with new mechanisms to focus awareness and attention on sea level change and to encourage nations of the world to develop appropriate responses.

6. Technical assistance for developing nations should be provided and cooperation stimulated. Institutions offering financial support should recognize the need for technical assistance in developing coastal management plans, assessing coastal resources at risk and increasing a nation's ability, through education, training and technology transfer, to address sea level rise.

7. International organizations should support national efforts to limit population growth in coastal areas. In the final analysis, rapid population growth is the underlying problem with the greatest impact on both the efficiency of coastal zone management and the success of adaptive response options.

Research, Data and Information

8. Research on the impacts of global climate change on sea level rise should be strengthened. International and national climate research programmes need to be directed at understanding and predicting changes in sea level, extreme events, precipitation and other impacts of global climate change on coastal areas.

9.A global ocean observing network should be developed and implemented. Member nations are strongly encouraged to support the efforts of the IOC, WMO and UNEP to establish a coordinated international ocean observing network that will allow for accurate assessments and continuous monitoring of changes in the world's oceans and coastal areas, particularly sea level change.

10. Data and information on sea level change and adaptive options should be made widely available. An international mechanism should be identified with the participation of the parties concerned for collecting and exchanging data and information on climate change and its impact on sea level and the coastal zone and on various adaptive options. Sharing this information with developing countries is critically important for preparation of coastal management plans.

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Strategies for Adaption to Sea Level Rise was originally published November 1990 by the Intergovernmental Panel on Climate Change, Response Strategies Working Group.

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