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Considering that the oceans are rising (and that humans don't seem too keen on doing anything about it) and that population is growing exponentially, is it plausible to imagine that in a not too distant future, cities will expand underwater?

  • If yes, how soon and at what rate? This question is not meant to entail the design aspects of such city unless it's relevant for the timeline (for technological development for example).

  • If no, why not? What are the more plausible alternatives for the growing population on a shrinking land?

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    $\begingroup$ Its not long enough to be an answer but: we will have underwater cities the moment it becomes financially profitable to run it. The maintenance cost of underwater and above water things is atrocious. $\endgroup$ – Cort Ammon Nov 27 '14 at 0:57
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    $\begingroup$ Any definition as to what qualifies as underwater cities? Do a city partially integrated into a shallow lake (yet still contain land components qualify) or are you looking for full isolated dome city at the far depths of an ocean? $\endgroup$ – Twelfth Nov 27 '14 at 1:00
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    $\begingroup$ fwiw, even if all the ice on Earth melted, it'd only be a 200-250 foot rise in sea level. Coastal areas would be screwed, but there'd be lots and lots of land left... plus the newly available land in Antarctica. $\endgroup$ – GrandmasterB Nov 27 '14 at 4:50
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    $\begingroup$ @GrandmasterB - 200-250 feet puts a country like Bangladesh with the highest population density 47% underwater. Nearly 800 million (pending where you get the figure, 650 million is conservative) live within that 200 feet marker of the sea. 1/4 of the american population would be underwater as well...The highest point on the island of Manhattan is 265 feet above. Only 200-250 feet submerges a good portion of us $\endgroup$ – Twelfth Nov 27 '14 at 17:20
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    $\begingroup$ A scenario for the need to build underwater cities may be a world-devastating nuclear war, or any other catastrophy that contaminates the atmosphere and/or the soil to grow food. Going underwater some tens of meters may be sufficient to shield from radioactive fallout. If food was grown under water too one could endure for quite a while without having to set a foot on the contaminated land. $\endgroup$ – JimmyB Nov 28 '14 at 16:07
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I love the idea, but heavily question feasibility.

My guess is in 50 or so years, it will appear in a place like London, but entirely as a status symbol // art project and not feasible for large style underwater cities.

It's a combination of safety and price. When you state the water levels are rising, the majority of the people immediately affected by it are too poor to attempt large scale underwater living, and are far more likely to live up on the surface in floating housing instead.

To the people that can afford it, there are simply far safer places to live (and they can afford to live there). Though we might be technically capable of doing it on a day to day living style, a disaster (earthquake? tsunami is in the ocean?) presents a nearly 100% loss of life scenario. Maintenance and the the constant damage to the structure would be a horribly high upkeep...at least until our knowledge of construction advances considerably.

On the water or underground seems far more likely to me

Adding:

As an odd side note to this...Stephen Hawking made a comment about space colonization being the route to save humanity...the faster we get to the stars, the faster humanity gets to a state where it can't be eliminated. This is based on a simple principle I like to refer to as human redundancy...we are currently 100% dependant on Earth as a species and an apocalyptic event on earth could end our species. If we were to setlle on...say a moon on Jupiter...something hugely traumatic could end life on Earth but still have Humanity as a species survive. Oceanic colonization isn't this degree of redundancy, though it does relocate some of us underwater, it does very little from a 'survival of humanity' standpoint. Not sure if thats really an arguement against oceanic colonization, but it does show we have other area's of colonization more suited to the 'survival of species' line of thought.

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Twelfth is right about the cost and safety issue, but I think that we could motivate the wealthy to speed up that timeline. Cost and Safety are both relative scales. That is to say that what constitutes an acceptable cost and an acceptable safetyl level is relative to the cost and safety of other, currently available alternatives. So let's get rid of a few of the cheaper, safer alternatives. Lets start small; a couple of years of draught in the major grain belts, food shortages, riots,... wars. Throw in a twist, a charasmatic leader with some serious strategic smarts, as commander to the world's starving hordes, turning them into an organized military force. Through raids against military armories and governement food stockpiles, that military force becomes an army; eclipsing the civil authorities and police protectors. The rich can no longer rest in thier ivory towers. It is time for them to run... and where better to run, than to the comforting concealment of the ocean depths. Underground complexes can be surrounded and starved out. Floating cities can be attacked by artillary and aircraft. The only safety lies beneath the waves.

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  • $\begingroup$ Underground bunkers and space seem like safer and cheaper alternatives than trying to make something that can withstand the pressures while maintaining a usable atmosphere inside. Every 10 meters below is around a 1 atmosphere pressure increase...perfect spheres have the best chance of resisting these, but a single structural fault is fatal (porthole pinhole). Modern atomic subs have a rated 'crush' depth of about 500 meters, no where near the bottom of the ocean floor...and any issue down to a pinhole would be beyond catastrophic. Good idea for an answer, not really feasible. $\endgroup$ – Twelfth Nov 27 '14 at 20:00
  • $\begingroup$ Why would an undersea city have to be deep? Highly mobile and invisible from the surface is all that is really needed. Yes, such a structure would still be trackable by satellites, survellience planes and radar, but that is still a much smaller profile than a floating city or a fixed bunker. I envy your space-city for its remoteness. Extra-planetary isolation is a big security boon. But I think the economics and danger of ferrying the wealthy back and forth from earth to orbit, would offset that security advantage. $\endgroup$ – Henry Taylor Nov 27 '14 at 20:47
  • $\begingroup$ I assumed ocean and not lake (figured under lake cities would be easier to spot and lose the isolation factor). Most ocean coastlines are sharp drop offs and there is little for plateaus in the 100m deep range. Even the Mediterranean averages a good 1500 meters deep. I'd be hard pressed to find a suitable location in the 100m deep range...maybe the English channel (though I'd argue against isolation there), but even then it possesses some decently sharp drop offs. Or are you going more of a "floating at a depth" underwater city and not on the ocean floor? $\endgroup$ – Twelfth Nov 27 '14 at 21:32
  • $\begingroup$ As to my 100m depth suggestion, if you are fleeing from a surface army, most depth charges are quite effective to 100m, with later american ones capable of taking out subs at 180m deep. I'd assume if your worry is a surface military, being under that would be a goal. $\endgroup$ – Twelfth Nov 27 '14 at 21:53
  • $\begingroup$ I had been envisioning "floating at a depth" because any location, regardless of the depth would be a strategic weakness if fixed. Highly mobile is the new "high ground". Hadn't considered depth charges though. I was sort of hoping that the attack against the rich would taper off after they got out of harms way. After all, financial wealth is little more than the ability to influence others in the real world. Once the rich run away from their businesses and their assets, are they really rich any more. Are they really worth chasing. $\endgroup$ – Henry Taylor Nov 27 '14 at 23:31
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The current answer to sea level elevation is a levee or dike.

This has already been done historically in the Netherlands (Polders). This is in progress in Venice (MOSE Project).

I bet that this will be the choosen solution as soon as Wall Street experiments acqua alta.

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Actually what is much more likely would be a large floating island city. Peter Thiel has already proposed such an undertaking and is trying to garner other billionaires to join in the project. This of course is with the idea to have a libertarian 'dream' but in my opinion it is another attempt at tax evasion. However, it is seriously being thought about and designed. Floating on top of the ocean will be much easier to do since that is something humans have been doing for 1,000s of years. Make the structure large enough and rough seas would be a much smaller problem (assuming they don't try to go around horn of Africa or something in bad weather)

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    $\begingroup$ Makes me think the lost city of Atlantis was just a Greek tax evasion scheme. $\endgroup$ – Twelfth Nov 27 '14 at 19:39
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    $\begingroup$ I believe one of the Pendragon books discusses this idea. $\endgroup$ – HDE 226868 Nov 28 '14 at 15:33

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