December 1, 2012

ON MONDAY, New York Gov. Andrew Cuomo (D) said that the response to Hurricane Sandy will cost $42 billion. On Wednesday, New Jersey Gov. Chris Christie (R) claimed that his state needs nearly as much. On the same day, a group of climate researchers released calculations that indicate the world’s oceans are rising 60 percent faster than the U.N. Intergovernmental Panel on Climate Change anticipated five years ago. Projecting how Greenland’s ice will behave in a warming world or what will happen to the polar ice caps decades from now is difficult. But sea levels appear to be on track to rise by several feet over the next century, with every inch putting more Americans at risk. Sea-level researchers Robert Kopp and Benjamin Strauss estimate that a five-foot rise would produce Sandy-like floods in New York every 15 years, on average.

Protecting New York City, America’s skyscraping metropolis, from the advancing ocean is likely to be one of this century’s great infrastructure investments. Some work, such as constructing sea walls and retrofitting subway entrances, is already happening. Part of Mr. Cuomo’s $42 billion request includes money to prepare for the next storm — funding for waterproofing electrical infrastructure, retrofitting sewage treatment plants or floodproofing subway tunnels. The last is especially important; damage to the subway system was the biggest-ticket item in the state’s cost estimates, topping out at $5 billion.

Ever-higher seas, though, probably require more ambitious planning. The cheapest item in certain areas might be raising building entrances or building up the land. Massive sea gates could block storm surges from entering upper New York Harbor, saving large swaths of the city. Other options for protecting the five boroughs include sinking old subway cars to create artificial reefs, building barrier islands and extending the shore where feasible. Cost-benefit calculations should begin immediately; the sea gates alone would cost something like $10 billion or more — a bargain compared with the cost of another big flood.

But in some ways New York’s challenge is relatively simple. Unlike many other areas of the country that will have to adapt to the varied and unpredictable effects of climate change, the city can have confidence that it faces a well-defined danger — rising seas — with effects that are possible to anticipate. Unlike less populated zones at risk of advancing water, it’s obvious that spending billions to protect this population center is a worthwhile investment. And, unlike other places, local officials have already started thinking seriously about engineering their way out of danger. A 2011 survey found that only 13 percent of American municipalities had even completed climate risk assessments.

In the coming decades, localities up and down the Atlantic coast, including portions of Maryland and Virginia, will have to wrestle with the question of which coastal areas are worth protecting — by raising land, lengthening beaches, heightening homes or building sea walls to keep the water out — and which aren’t. Sea walls won’t make sense everywhere; they are expensive, and they can harm crucial habitats that support America’s coastal ecosystems and fisheries. The first thing federal and local officials can do is reverse policies that encourage more coastal development without properly accounting for sea-level risks. Another is planning ahead to a time when some land will inevitably be given up to the ocean.

For economic, recreational and aesthetic reasons, Americans have clustered on the shore. Even in stable climatic times, the coastline is dynamic, wetlands teeming with life, barrier islands shifting, all the while subject to big storms and associated floods. Increasingly, though, the climate will not be stable. Communities from lower Manhattan to the Delmarva Peninsula will have to confront that reality. Best to start now.