LONDON — We are a coast-hugging species. About 44 percent of the world's population live beside the seaside, and that number is set to rise. Why? Maritime commerce and easy access to all that lovely seafood spring to mind. But maybe there's a more fundamental reason, a human instinct touched upon by the sailor Ishmael, explaining his aquatic affection on the very first page of Moby Dick: "If they but knew it, almost all men in their degree, some time or other, cherish nearly the same feelings towards the ocean with me."

Unfortunately, the sea doesn't always return that tender affection. Like the number of coast-huggers, it too is set to rise. Between 1950 and 2009, global coastlines rose between 0.6 and 1 millimeter annually. Taken together, those two trends spell global disaster, albeit of the very, very gradual kind. So what if the sea swallows up a low-lying atoll here and there? Who cares if entire (albeit tiny) Pacific nations may be engulfed in a few decades? If it happens slowly enough for the victims to row away to safety, it surely happens too slowly for anyone else to notice. So, if you're a low-lying island nation, you probably need a clever media stunt for the world to pay any attention.

But add a noticeable rise in extreme weather to those creeping sea levels, throw in a high tide surge, and you've got Superstorm Sandy. Suddenly, New York looks eerily like it does in all those apocalyptic movies that were enjoyable because they seemed distant enough. Director Roland Emmerich's cinematic schadenfreude feels like a guilty pleasure now. It won't forever.

New York will survive, get on with business, and Sandy will recede in memory. But from now on, New Yorkers won't be able to say Mother Nature didn't give them notice. Folks in New Orleans got a similar, albeit more distressing, wake-up call in 2005 from Hurricane Katrina. In both cases, the storms are forebodings of the cities' future demise. Nothing is eternal. Like people and countries, cities too eventually kick the bucket. The likeliest scenario for New Orleans and New York is that they will die a watery death, swallowed up eventually by the otherwise life-giving sea. The waters will rise, steadily but imperceptibly, while Poseidon will occasionally reach into his war-chest for tempests to whack their defenses with — until they break.

Not that the Greek sea god is a sort of pagan Osama bin Laden, who has a special bone to pick with the United States. The list of metropoles threatened by rising seas and freak storms is alarmingly long, if (from a U.S. viewpoint) reassuringly international. Some of the world's other great cities regularly threatened by coastal flooding, and long-term candidates for watery extinction, are:

Mumbai, India: 2.8 million inhabitants exposed to flooding

Shanghai, China: 2.4 million exposed

Miami, United States: 2 million exposed

Alexandria, Egypt: 1.3 million exposed

Tokyo, Japan: 1.1 million exposed

Bangkok, Thailand: 900,000 exposed

Dhaka, Bangladesh: 850,000 exposed

Abidjan, Ivory Coast: 520,000 exposed

Jakarta, Indonesia: 500,000 exposed

Lagos, Nigeria: 360,000 exposed

But this accounting doesn't include several notable cities. London is not on the list, perhaps because of its state-of-the-art Thames Barrier, the world's second-largest moveable flood gate (after the Dutch Oosterscheldekering), which is nevertheless predicted to lose its protective function by 2050 due to rising sea levels. The artist Michael Pinsky earlier this year provided a poignant reminder of that future threat: his project Plunge encircled noteworthy London monuments in blue neon at the sea level predicted for the year 3111 — 90 feet above its current height.

Also absent from most soon-to-be-inundated lists is St. Petersburg. The former Russian capital was built on the marshy meeting point between the River Neva and the Baltic Sea, an area so flood-prone that it inspired one of Alexander Pushkin's most famous poems, "The Bronze Horseman." It tells of a grief-stricken flood survivor whose girl has drowned, cursing the equestrian statue of the city's founder, Peter the Great, who promptly comes to life to chase the protagonist to his death. To combat the recurring floods — more than 300 since the city's founding in 1703 — Russia's "Window on the West" is now framed by a sea wall that doubles as part of the city's ring road.

Sea walls are the most expensive solution, and the only one enabling coastal cities to claim a victory over the sea, however tenuous and temporary. But while Manhattan could feasibly find the money to construct such fortifications, other flood-prone cities might not have the financial wherewithal to construct similar defenses, and may have to resort to strategic accommodation. According to the U.S. Global Change Research Program, coastal cities can either choose to work around the rising water by staying put, elevating parts of the natural and built environment; or beating the retreat as the shoreline inevitably advances inland.

In the Netherlands, which pioneered the expensive sea-wall solution, public debate nevertheless occasionally flares up about giving parts of low-lying wetlands, marshlands and farmlands — won so dearly over the centuries — back to the sea. Rising tides do imply a rising cost of maintaining the status quo.

Nowhere is that lesson more keenly felt than in Venice. Since its founding in the 6th century on an Adriatic archipelago as a refuge from the marauding Ostrogoths and other barbaric invaders, the city whose streets are paved with water has been sinking at an average rate of 1.5 inches per century. But now rising sea levels are combining with the area's naturally soft foundations to accelerate the sinking by as much as five times the previous rate.

The MOSE Project, slated for completion in 2014, is a sea wall similar to the British, Dutch and Russian examples. When finished, it will be able to close off the laguna containing Venice, safeguarding it from high tides. The project is controversial (not to mention expensive, at some 4.7 billion euros), though, and its critics continue to push alternatives, like the scheme to pump the Venetian underground full of sludge to stop the city from subsiding.

Until it's saved — or disappears beneath the waves — Venice will remain the emblematic Sinking City. But maybe the romance of the place will wear off a bit as more and more coast-huggers start to relate to it after their cities experience their own defining Katrina/Sandy moment. As coastal cities grow, sea levels rise and extreme weather increases, we're discovering that we are all Venetians now. There's still time for governments and civic leaders to embark on the serious projects needed to protect their cities from Mother Nature. But this is a tale that doesn't always end well. Just about every folklore tradition in the world has a story about a sunken city, the bells of which can still be heard during storms. Perhaps some day those bells will toll for us.

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Jacobs is a London-based author, journalist, and blogger. He writes about strange maps, intriguing borders, and other cartographic curiosities.