In a slightly future Earth I want to explore undersea colonization, but I need strong plausible incentives to emerge and convince people to do it. I could entertain societal, economic, geopolitical, technological, geological or other factors or combinations of these. I do not want just one eccentric billionaire or dictator with a crazy idea; but a sane reason that would encourage many independent groups to begin building undersea colonies.
closed as too broad by L.Dutch♦, Mołot, Frostfyre, sphennings, Azuaron Jul 26 '17 at 17:42
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As Alexander pointed out, the technological challenges are substantial. So there would have to be an even more powerful factor to push for undersea development.
- Interested parties might create legal precedents that a seafloor settlement outside the EEZ of any existing nation does constitute a new, sovereign nation. That means building the settlement, not provoking any major power, and getting expensive lawyers.
- Global warming causes the flooding of some island nation. To preserve their sovereignty and EEZ, they build a seafloor settlement. The ground happens to be more stable a couple of kilometres off the shore, and not directly in the surf.
For all I know the sea, i.e. very large amounts of water, provides an excellent radiation shield.
So, a credible driver for underwater colonization might be increased radiation levels, for example due to a missing ozone layer.
It would also help with credibility of the whole setup.
Building a habitat for humans under the sea is technologically challenging, to say the least. At 100 m below the surface you have approx. 11 bar of pressure, some 11 times more than above the water. This constitutes not only massive load on any structure you build, most of all on the outer shell, it also provides extreme hazards in case of a breach of the outer hull.
None of that is impossible, but it's difficult, which equates to expensive.
It also means it cannot be done in a hurry, but you would need a few decades to build structures large enough to count even as a city, not to mention widespread colonization, as you ask for. Obviously, fear of an ugly death is a strong driver for such development, especially when it is paired with enough time to not only react but also to handle the notorious deniers.
So, the setup I would suggest would be that for some technobabble reason, the ozone layer is depleting. That is clearly noticeable, not reversible, and will continue to eventually become lethal for most life in the scale of 50 years or such.
As a radiation shield, you don't really need 100 m of sea water. You might also want to be able to make use of the harmless radiation, i.e. light, because it is mightily convenient. So I suggest your colonization starts in fairly shallow waters, on the continental shelves. That also facilitates construction, moving people and things back and forth, and whatnot.
After the first habitats are built, the technology will advance, as is always the case: do something often enough and you will get better at it.
Gradually, you can move more people into those habitats, providing at first part-time shelter, and then more and more as your facilities grow, while in the meantime your ozone layer becomes ever thinner, speeding the need to move under the sea while at the same time being able to provide room for ever more people.
So, to sum it up: The main driver could be ozone depletion and the resulting increase in radiation (UV mostly).
What would it look like: Mostly tubes and bubbles, to survive the pressure. On the inside: Anything you darn well please. And a realistic timeline might be half a century.
Undersea development is possible. Undersea colonization, with present technological level - no.
Building human habitat on the ocean floor is possible, but very technologically challenging. Even in shallow (<100m) waters, it is much more convenient to have above the see level platform and perform all bottom activities from there. A large scale mining of solid ores may require an actual base on the floor. Or it may not - it will all be decided by economics.
Colonization is different from exploration and mining. Colonization assumes that a colony could be self-sustainable, and we are not at this level quite yet. Colony requires energy, air, fresh water, food and other basic necessities. We can potentially have a nuclear reactor and derive all other things from its energy, but this setup would be expensive and potentially unsafe.