Photograph by Bebeto Matthews, AP Photo

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A surge of seawater floods New York City streets during Superstorm Sandy, October 2012.

Photograph by Bebeto Matthews, AP Photo

New York's Sea-Level Plan: Will It Play in Miami?

Rising seas threaten other cities more than New York.

Mayor Michael Bloomberg's announcement yesterday of a $19.5 billion, multidecade plan to defend New York City against rising seas and severe storms illustrated two truths that resonate far beyond his home city.

First, as the time when we could prevent dangerous climate change slips away, the time for costly investments to protect ourselves has arrived. Second, for some cities, less well situated or less wealthy than New York, protection is going to be extremely challenging—and in some cases perhaps impossible.

Speaking at the Brooklyn Navy Yard, which last fall was inundated by the storm surge from Superstorm Sandy, Bloomberg warned his audience that by the middle of this century, storm tides may be riding on a sea that is two feet higher than today. According to new maps released by the Federal Emergency Management Agency this week, a quarter of the city—where some 800,000 people now live—will lie in flood zones. High tides will routinely inundate much of the waterfront, even without a storm.

That's if nothing is done to stop them. "As New Yorkers, we cannot and will not abandon our waterfront," Bloomberg said. "It is our greatest asset." His $19.5 billion plan—the price tag matches almost exactly the damage inflicted on the city by Sandy—calls for the construction of permanent levees, sand dunes, portable storm barriers, and other climate defenses. Visitors to lower Manhattan in coming decades may find a Dutch-style dike between them and the harbor.

It will be a big change. And after the devastation wrought by Sandy it may seem strange to say this—but New York is actually pretty lucky. "New York is not in as bad shape as many other delta cities—it's above sea level and built on solid ground," says Piet Dircke, an executive with Arcadis, a Dutch engineering firm that has designed flood-control projects on nearly every continent. Some of the world's other coastal cities, Dircke says, face far graver threats from sea-level rise.

An Uncertain Tide

Climate scientists don't know how high the seas will rise in the decades ahead. According to a report released last December by the National Oceanic and Atmospheric Administration, we can expect to see as much as 6.6 feet (2 meters) of sea-level rise by 2100, though a lower figure is more likely.

A report prepared a few years ago for the Organisation for Economic Co-operation and Development (OECD) estimated that 40 million people and $3 trillion in assets are already vulnerable to coastal flooding in cities around the world. By 2070, the OECD paper said, those numbers could rise to 150 million people and $35 trillion—and that's assuming a sea-level rise of just 20 inches (0.5 meter).

New York has taken the threat much more seriously than most American jurisdictions. At least one state, North Carolina, is actively ignoring the problem: The state legislature has refused to include realistic sea-level rise projections in its coastal planning policies.

Even with enlightened leadership, however, the sorts of engineering solutions proposed by Bloomberg won't work everywhere. Miami, for example, which tops the OECD report's list for cities with the most assets at risk, rests on a foundation of highly porous limestone. Seawater would flow unimpeded beneath any levee or storm surge barrier.

It's already contaminating Florida's underground water supply, and it regularly erupts from Miami's sewers during "king tides," when the sun and moon exert their most powerful tidal pull on Earth. The problem is only going to get worse: By the century's end large parts of Florida may be underwater.

Even where levees and barriers can be built, they may not be able to save the cities behind them. New Orleans, though it is now shielded by a number of new flood-control projects constructed after Hurricane Katrina, will be increasingly exposed to storms and floods in decades to come, as the Mississippi delta continues to sink into the Gulf of Mexico. Louisiana has formulated a $50 billion plan to try to restore the disappearing coast. But even if the money becomes available, it's far from clear to some experts that the loss of land can be reversed.

"The can-do attitude won't work on the Mississippi delta," says Orrin Pilkey, professor emeritus of geology at Duke University and co-author of The Rising Sea. "What we should be planning on is how to get out of there gracefully."

Asian Cities Hit Hardest

Tragically, some of the world's poorest and most crowded cities will also be subjected to the greatest changes in sea level. There are two reasons for this, one of them quite surprising.

Global sea-level rise is caused by the melting of ice on land and by the fact that seawater expands as it gets warmer. As the ice sheets on Antarctica and Greenland melt, though, the liberated water won't be distributed evenly around the globe. With less ice cover, Greenland and Antarctica will become less massive, and their gravitational pull on the surrounding seas will decrease, causing water to pile up in the tropics.

To avoid sea-level rise, a good city to move to would be Reykjavik, Iceland. As the nearby ice sheet in Greenland dwindles, the sea level in Iceland is actually expected to fall.

Some of the worst places to move, in terms of the threat from rising seas, are the very cities that poor people are actually streaming into in search of economic opportunity—cities along the tropical Indian Ocean and western Pacific. Not only can those cities expect to get more than their fair share of the water from melting ice in Antartica, but also some of them are built, like New Orleans, on rapidly subsiding river deltas. Where the land is sinking, the rate of relative sea-level rise is often far higher than the global average caused by the increased volume of water in the ocean.

Calcutta, India; Ho Chi Minh City, Vietnam (formerly Saigon); and Dhaka, Bangladesh, are all delta cities. All three are in the top five of the OECD's list of cities projected to have the largest populations vulnerable to sea-level rise by the 2070s.

With three feet of sea-level rise—a distinct possibility by 2100—large parts of Bangladesh will be uninhabitable. According to the Intergovernmental Panel on Climate Change, rising sea level may create 20 million to 30 million refugees in the country even by 2050. Where will they all go? "The implications for Bangladesh are enormous," says Jeroen Aerts, a climate researcher at the Free University in Amsterdam. "We're not talking about one city—it's a whole society that will be impacted."

Beer and Sea-Level Rise

Jakarta, the capital of Indonesia, barely slipped onto the OECD list at number 20. Whereas Calcutta may have 14 million people exposed to coastal flooding by 2070, according to the report, Jakarta will have a mere 2.2 million—up from half a million today.

But Jakarta is particularly vulnerable, Piet Dircke says. Forty percent of the city lies below sea level. It's a delta city traversed by 13 rivers, which are fully capable of flooding the city even without help from the sea. A flood in February 2007 caused by torrential rains inundated 70 percent of the city, displacing 220,000 people and killing 79.

In Jakarta's case land subsidence—some parts of the city are sinking by nearly a foot every year—is aggravated by intensive extraction of groundwater. The Dutch, so often turned to for solutions to sea-level rise, are a small part of the problem here. "Our famous Heineken brewery in the middle of Jakarta pumps groundwater to make beer, and all around it buildings are sinking," Dircke says. "Building a great seawall won't help Jakarta unless they do something about their water supply."

Even the most advanced and ambitious engineering projects may not save some of those cities from disaster. Dircke says that many nations simply don't have the money or expertise to protect themselves against rising seas, even with the most well-intentioned help from other nations.  "One of my biggest worries for some delta cities is that we go in and build some structures and create a false sense of security. The projects could be beyond the ability of some countries to maintain."

Defending a nation against climate change and sea-level rise, he says, is not merely a technological challenge, but also a cultural one. "We Dutch have been doing this for 500 years," says Dircke. "Our technical superiority is based on our political system. Water management for us is above politics—almost. People ask, can you export the Dutch model? Can you wrap it for me? Well, you can't. Not without governance."

At least in New York (formerly known as New Amsterdam), the necessary cultural shift seems to be beginning.