Planning for the impacts of sea level rise

Coastal areas constitute important habitats, and they contain a large and growing population, much of it located in economic centers such as London, New York, Tokyo, Shanghai, Mumbai, and Lagos. The range of coastal hazards includes climate-induced sea level rise, a long-term threat that demands broad response. Global sea levels rose 17 cm through the twentieth century, and are likely to rise more rapidly through the twenty-first century when a rise of more than 1 m is possible. In some locations, these changes may be exacerbated by (1) increases in storminess due to climate change, although this scenario is less certain, and (2) widespread human-induced subsidence due to ground fluid withdrawal from, and drainage of, susceptible soils, especially in deltas. Relative sea level rise has a range of potential impacts, including higher extreme sea levels (and flooding), coastal erosion, salinization of surface and ground waters, and degradation of coastal habitats such as wetlands. Without adaptation, large land areas and millions of people could be displaced by sea level rise. Appropriate responses include climate mitigation (a global response) and/or adaptation (a local response). A combination of these strategies appears to be the most appropriate approach to sea level rise regardless of the uncertainty. Adaptation responses can be characterized as (1) protect, (2) accommodate, or (3) retreat. While these adaptation responses could reduce impacts significantly, they will need to be consistent with responses to all coastal hazards, as well as with wider societal and development objectives; hence, an integrated coastal management philosophy is required. In some developed countries, including England and the Netherlands, proactive adaptation plans are already being formulated. Coastal cities worldwide will be a major focus for adaptation efforts because of their concentrations of people and assets. Developing countries will pose adaptation challenges, especially in deltaic areas and small islands, which are the most vulnerable settings