Possible responses to increasing risk from accelerating sea level rise

There are several conceivable approaches for dealing with the threat of rising sea level:

• The do nothing approach. The do-nothing approach is based on a wait-and-see attitude by coastal planners in the hope that nothing catastrophic will happen on their watch. Many risk analyses and cost-benefit studies are completed, but in the end, insufficient political will or funds are available to proceed with raising large amounts of money to build urban coastal defenses for catastrophic storm surge events that may never happen. This is the most common scenario for nations without a strong tradition or commitment to spend federal monies for regional coastal protection against natural hazards.

• The iterative approach. This centers on fixing problems on a case-by-case basis as they arise, for example, patching up and strengthening leaky seawalls, modifying transportation routes, raising airport runways and building new seawalls around facilities, raising subway entrances and ventilation shafts prone to flooding, protecting other underground infrastructure related to energy and communications, pumping out backed-up sewers and so forth. This approach is analogous to patching up potholes on the highway - the basic roadway is in good repair, but weak spots showing signs of wear and upheaval due to adverse weather keep popping up and must be repaired to eliminate or minimize safety hazards. This method is the most responsive to relatively modest amounts of municipal funds becoming available from time to time and that must be spent or be lost from the budget.

• The regional approach. At times, the iterative approach may become large scale in nature. For example, the Dutch have been busily reclaiming and protecting their lowlands for centuries by creating an intricate network of dikes surrounding low-lying tracts of land known as polders, then pumping out the sea and turning the land into useful pasture and even cities. Amsterdam, the capital city of The Netherlands, whose urban area is home to 1.2 million residents, in places is built on land as much as 5.5m (18 ft) below mean sea level. One half of the country's land area is now reclaimed from the sea. After a devastating flood that took 3000 lives in 1953, the Delta Project was begun, and a series of large barriers were constructed around the southeastern coast, connected by high seawalls. Clearly, once a decision has been made to protect a city or state against storm surges and rising sea level with moveable barriers, levies and seawalls, there is no going back. The commitment is forever. The Dutch made that commitment centuries ago and have a highly professional and established engineering, marine hydraulics and governmental infrastructure dedicated to building, maintaining and improving the country's coastal defenses against the sea.

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