What Today's Sinking Cities Tell Us About The Future Of Rising Seas

Venice

We've already seen Manhattan swallowed by surging waves as glaciers collapse and drive sea levels sky-high—on video screens and in nightmarish daydreams about human-driven climate change. But what will sea level rise really be like for a coastal metropolis of the future? It's actually easy to answer that question yourself, not with a ride in a time machine but simply with a trip in a car, boat, or plane. Visit any of more than a dozen coastal cities around the world and you'll soon get a first-hand taste of what's coming. But be forewarned; it's probably not as thrilling as what you've seen on TV.

We often hear about how high the sea could rise as ice sheets thaw and crumble. If we switch quickly to non-fossil fuels, the sea level should rise about as much as it did during the naturally warm period before the last ice age, roughly 20 feet or so. If we burn all of our remaining coal, then all land-based ice will vanish and the sea level will stand over 200 feet higher than today.

We rarely hear about the slow pace of such changes while gaping at disaster flicks, or at the so-called "flood maps" that show America with the thumb of Florida bitten off as if by sharks. If the thought of catastrophic climate change finally makes you so depressed that you chuck everything and simply wait on your favorite beach for the Great Flood, you'll certainly perish there. But not from drowning; you'll die of old age long before the ocean overtakes the trees or buildings around you.

Sea level is currently rising by about three fingernail thicknesses per year, and it climbed about seven inches during the entire 20th century. Nobody knows exactly how much it could speed up during this century; the high end of the prediction spectrum suggests another 15 feet or so by 2100 AD. But most of the estimates coming from experts who study this topic for a living put the range closer to two or three feet by century's end. That averages out to about two or three inches per year.

In other words, if you're going to sit on the beach and wait for the 10-foot-high roof of the hot dog stand behind you to disappear, you're going to have to wait between 300 and 1,000 years, so you'd better bring plenty of cash to pay for all of those hot dogs you'll be eating in the meantime.

Now, don't get me wrong. Sea level rise is a horrible outcome of human-driven warming. But not in the way you may be thinking of it. It's not so much a crashing apocalypse as it is a chronic problem, more like a slow cancer than a sudden heart attack. We still need to do all we can in order to prevent as much of it as possible, but we also need to realize that it's going to take a long time. This is not to remove all concern about the issue, but rather to help us recognize that the slow pace of these changes can mask their seriousness. And it also means that this is going to bother us and our descendants for a very long time—probably for thousands of years.

So what's it really going to be like to live in a coastal city from here on out? You might ask residents of the American Gulf Coast, much of which has been sinking faster than the ocean rose during the last century, thanks to groundwater extraction and removal of oil and gas. Some sites around Houston, for example, have recently started sinking by more than an inch per year, though you wouldn't know it from the scarcity of media coverage about that long-term "slow-pocalypse" (PDF).

Or consider Tokyo, which sank about 10 feet during the last century. Some sites near the harbor are subsiding by more than four inches per year. China's largest coastal city, Shanghai, sank about 9 feet deeper into the Yangtze delta over the last hundred years. And Bangkok is sagging by four or five inches per year, which is over twice as fast as the inundation in a worst-case future and forty times the rate of today's sea level rise. In these and a surprisingly large number of similar places, the sinking of the ground has much the same effect as a rising of the sea surface, and the magnitude is often greater than what we worry about from climate change. It's been costing some cities billions of dollars in dikes, pumps, and repairs for many decades already. It has become such a chronic problem in Texas that the state legislature has officially designated a "Coastal Subsidence District" around Galveston.

Clearly, this is a severe drain on resources that most towns would surely prefer to do without. Unless, perhaps, you raise the topic with residents of Venice. The soft sediments beneath the city are dropping twice as rapidly as the sea is rising, and the streets have been flooded for centuries. But urban life in Venice is not paralyzed by this, and tourists don't flock there in order to gawk at the devastation of a city gone under. By now, Venetians are used to it and I suspect that, given a choice, most of them would keep things much as they are. Of course, that might change when even faster sea level rise kicks in and piles on top of their existing problems.

Or consider Amsterdam. Roughly two thousand years ago it was a nondescript bit of rural landscape isolated from the ocean by miles of low-lying coastal plains. When naturally rising sea levels eventually formed what is now the Zuiderzee harbor, they also opened a route to the shipping lanes of the North Atlantic and Amsterdam was transformed into a bustling hub of commerce and culture. Even as we lose today's Big Easies and Shanghais, tomorrow's nascent Amsterdams will spring to life in the "zone of anticipation" that precedes the waves. Centuries later, they too will succumb to submergence, and so on it will go.

This is not a future that most nations would choose, nor should they have to. Fortunately, we still have time to keep most of today's seaside settlements above water, albeit not without somewhat of a dunking in the lowest areas—if we switch to carbon-free fuels as soon as possible. Our distant descendants, if they think of us at all, might thank us as they twirl their pasta in the canal-side cafes of an even-more-ancient Venice or only-partially-waterlogged Manhattan in 5000 AD.

Curt Stager is an ecologist, paleoclimatologist, and science journalist with a Ph.D. in biology and geology from Duke University. His new book is DEEP FUTURE: The Next 100,000 Years of Life on Earth (St. Martin's Press, March 2011).

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3 Comments

  • Charles Higley

    First off, subsidence is not always due to water or gas and oil extraction. Some regions simply were never meant to have heavy buildings built on them and they subside regardless of what we do. The politically correct approach is that it is always our fault. Politically correct usually hides something, such as the fact that land can subside on its own due to masses placed on top.

    Second, we have:
    "But most of the estimates coming from experts who study this topic for a living put the range closer to two or three feet by century's end. That averages out to about two or three inches per year."

    The math here sucks big time. Three feet is 36 inches. Divide by 100 and you have 0.36 inches per year, not 2–3 inches. However, if you want to alarm people do a bad job on the math. 2–3 inches a year is 17–25 feet in a century! The original expert estimate pales in light of bad math conclusions!

    Much of the global warming sea level predictions are based on bottom up sea water expansion as oceans warm. Here, the IPCC assumes expansion of the full depths of the oceans. Firstly, the oceans are cooling not warming and, secondly, only the top few 100 meters of the oceans change temperature on a decadal basis and thermal expansion becomes a tiny factor. Take this and the fact that the Arctic ice has no effect on sea level, Greenland is not losing mass, and the Antarctic is gaining ice, sea level is not a worry. In recent years sea level has ceased rising and may even be decreasing, but to mention this takes away from the alarmist message of panic.

  • Matt Macarewich

    I'm just about 50 and was born and raised in a coastal community. When I was 8 (ish) I would fish in the harbor at the base of a sea wall which was usually exposed during mid tide. My 8 year old son and I were just standing in the same spot the other day, at mid tide. In forty years I have seen no change in sea level. Maybe inches, but at the rates this artical states, no way. I think globally regions coastal or not mainly rise and fall due to geological events. It seems the global warming spin sure makes a lot of so called experts a good living. More power to you. I guess?

  • Charles Higley

    Sea level rise has been amazingly constant over the last 200 years. Reports of increased rates of rise are simply lies. In fact, the rate has not only slowed recently, but has gone negative for the last almost two years. Thus, predictions of rise, articularly those based on the truly worthless, fatally flawed computer models or the junk science/alarmist statements of the IPCC are false and only designed to alarm the public to serve their political agenda.

    CO2 cannot and does not drive climate. Very simply, a trace gas cannot control climate In fact, thermodynamically, increased CO2 causes no warming and possibly a very slight cooling. It is plant food and we need it very much to fertilize our crops as we go into the next 30 years of cooling. That's right cooling due to natural cycles of the oceans and the Sun.

    The only reason the warmists like and want to blame CO2, ignoring all ohter much bigger factors, is that by ignoring or discounting everything else, they can blame any climate changes on man's activities. Does it not bother you that they claim everything of every kind is due to a 0.5 deg C of warming, the same rate of warming per century as we have had since the end of the LIttle Ice Age. It was warmer in the Medieval Period and civilizations had a great time.

    The global warming scam is a political agenda aimed at creating a case, based on a patently false assumption that CO2 can drive climate, for a Draconian usurptation of power and wealth by a crisis-appointed one-world government. Why else do you think that, after the failure in Copenhagen in 2009, the UN idiots have Schellnhuber laying out plans for a one-world government in which all nations have to submit to a central planning body which wants to transform every aspect of our societies into the vision of a small group of "wise" men. Since when is a totalitarian, socialist government run by a gang show any hope of being good for anybody not in the gang? No democracy, no choice, no freedoms, no capitalism or free trade, just daily edicts from on high just as they do in the European Union (they issue on average one regulation a day).