Sea-Level Rise and Coastal Zone Management

In this paper, Robert J. Nicholls assesses the situation in other parts of the world, arguing that many cities, such as London, New York, Tokyo, Shanghai, and Mumbai, are threatened by sea-level rise. After a 17 cm (6.6 in) rise in the twentieth century, Nicholls predicts that sea level will rise about 1 m (3.28 feet) in the twenty-first century. Without any policy responses, large land areas and millions of people will be displaced by increasing sea levels. Yet Nicholls admits that predicting the exact outcomes is difficult because of three factors.

First, cities built on deltas are likely to face more severe coastal flooding or erosion than other coastal areas because of collateral land subsidence. This subsidence may be caused by plate tectonics, glacial isostatic adjustment, or natural and anthropogenic-induced sinking. Because these nonclimate factors play out differently in various regions and are hard to predict correctly, Nicholls proposes that relative sea-level rise instead of global average trends should be used to assess potential effects on subsiding deltas. Second, sea-level rise also depends on the melting of land-based ice, the thermal expansion of ocean waters, and changing ocean dynamics. These natural changes are difficult to forecast. Third, proactive mitigation and adaptation policies could reduce impacts. Hence, the effectiveness of policy responses to climate change could alter the final outcomes. Owing to these uncertainties, anticipating the actual effects of sea-level rise caused by climate change is difficult.

Nicholls asserts that appropriate responses to sea-level rise require a combination of mitigation and adaptation. Some developed areas, such as London, The Netherlands, and Hamburg, Germany, have already formulated proactive adaptation plans. They represent optimistic situations in which investments in climate protection infrastructure have a high benefit-cost ratio. The main challenge remains in developing countries, especially in deltaic settings and small islands, where high adaptation costs can overwhelm government capacity and local economies. Nicholls labels them as the pessimistic situations.

This paper was presented at the Lincoln Institute’s Land Policy Conference of 2010 and is Chapter 3 of the book Climate Change and Land Policies.