Ian Koblick hoped the colourful seaweed samples he brought into class would impress. His marine biology professor at Stanford University commented on their beauty and asked where he had found them. Ian replied that he had collected them while exploring off the Californian coast using the Aqua-Lung, an early version of today's scuba equipment. His tutor dismissed his innovative approach. "Diving is for daredevils," she reprimanded. “If you want to be a real scientist, collect like a scientist.”

The year was 1962, and it did not take long for her words to seem antiquated. Jacques-Yves Cousteau's exploration of shipwrecks, discovery of previously unknown marine flora and fauna, and invention of novel deep-sea exploration tools had already captured public imagination worldwide. A wave of interest in undersea exploration was washing over the scientific community. There was serious talk of creating colonies on the bottom of the sea.

As for Koblick, he disregarded his professor’s advice and went on to become an ocean explorer and aquanaut. Ten years later, he opened La Chalupa, then the largest and most advanced underwater habitat and research facility at the world. Since then, however, interest in sending humans underwater for extended periods of time has ebbed. Of more than a dozen underwater habitats that once existed, just three remain, all in the Florida Keys. Koblick and his collaborators own and operate two of them – the Marine Lab, which is used as a research and training base by the likes of the US Navy and Nasa, and the Jules Undersea Lodge, which offers everything from education and training facilities to undersea weddings and luxury romantic getaways at $675 per night.

Creating larger-scale underwater habitation wouldn’t only benefit research (or indeed romantic getaways). Proponents maintain it could help alleviate over-population problems, or guard against the possibility of natural or man-made disasters that render land-based human life impossible. The question is how feasible this actually is.

Under pressure

According to Koblick, the technology already exists to create underwater colonies supporting up to 100 people – the few bunker-like habitats in operation today providing a blueprint. “There are no technological hurdles,” Koblick says. “If you had the money and the need, you could do it today.” Beyond that number, technological advances would be needed to deal with emergency evacuation systems, and environmental controls of air supply and humidity.

With safety being paramount, operators assure underwater habitats are running smoothly by monitoring life support systems – air composition, temperature and humidity – from the surface. Above the National Oceanic and Atmospheric Administration's Aquarius Reef Base, the third of the three existing facilities (which accommodates up to six aquanauts at a time), a bright yellow circular disc tethered to the undersea lab 60ft (18m) below collects data from a variety of sensors and sends it to shore via a special wireless internet connection. Future habitats could use satellites to communicate this important information. For now, energy independence is still a challenge. Sustainable future options might include harnessing wave action or placing solar panels on the surface.

Making larger habitats with multiple modules made of steel, glass and special cement used underwater would be simpler than trying to create one giant bubble. These smaller structures could be added or taken away to create living space for as many people as desired. Most likely, we wouldn’t want to build any deeper than 1,000ft (300m), because the pressures at such depths would require very thick walls and excessive periods of decompression for those returning to the surface. Koblick and his colleagues did not experience any ill effects from living below the surface for around 60 days, and he thinks stints up to six months would be feasible.

The air composition needed to sustain the aquanauts depends upon the depth of the habitat. The current habitats use compressors to constantly push fresh air from the surface down tubes to the habitat. A chemical product called Sodasorb is added to react with, and therefore remove, carbon dioxide. Below certain depths extra measures would be needed to ensure healthy ratio of oxygen to other gases in air – around 500ft (150m) for nitrogen and below around 1,000ft (300m) for helium. This is because the body requires different levels of different air components when at pressure. To become self-sustaining, future habitats could potentially grow plants using natural or artificial light to generate a fresh supply of oxygen, or develop other methods to produce their own oxygen.

Residents of underwater habitats can explore and study their watery surroundings for long periods using hollow tubes connecting their face masks or helmets and their living quarters. As well as allowing them to breath at depth, these "hookah lines" also facilitate communication. Aquarius uses lines of up to 400ft (120m). Alternatively normal scuba tanks can be used, and exchanged every hour or so.

Fresh seafood is generally easy to come by on the bottom of the ocean. Aquanauts regularly spear fish and eat plankton, while canned, preserved and dehydrated foods stock the shelves. Cooking underwater, although possible, is usually avoided because of the smells it gives off. Like in an airplane, fumes seem stronger in static air. Aquarius transports freshwater from the surface, but water could be created using condensation or desalinisation. Depending upon the size of the colony, human waste could be treated and released into the environment, or cooked down to a fine ash.

Deep dive

Many marine biologists are enthusiastic about the possibility of being able to live underwater. “There are a number of scientists who firmly believe that the only way to really understand what’s happening in the oceanic environment is to be there,” says Tom Potts, director of the Aquarius Reef Base. “Divers from the surface have about an hour-and-a-half per day to do all of their work. If we could actually inhabit the bottom of the ocean for 30 to 60 days, imagine the productivity we could get out of researchers down there.”

An example of the benefits came in the mid-1990s when a research group at Northeastern University, Boston, was seeking to understand the basic mechanisms behind the growth and feeding of coral. They found that doing their tests in a lab introduced all sorts of artificial effects, and that attempts to do them using boat dives failed because using scuba equipment did not give them the two to three hours they needed to set up chambers in which they wanted to produce different sea water flow rates around the coral. Shifting the experiment onto the Aquarius base allowed them to calculate optimal water flow rate for coral feeding.

It’s not just marine biologists that would benefit. Underwater archaeologists could take their time resurrecting sunken ships or searching for lost artefacts. Astronaut training has taken place in the existing underwater habitats since the isolated environments can be used to simulate living and working conditions in space. They can also act as broader educational tools. Students can visit them, or teachers can inspire them with video lessons from the bottom of the sea. Koblick converted the former La Chalupa research laboratory into the Jules Undersea Lodge as both a luxury hotel and educational facility. “Giving more people the opportunity to observe the underwater environment and get a feel for living there would help promote the oceans by getting people more interested in those habitats,” he says.

There is growing interest in deep sea mining for minerals and metals, especially around island nations such as the Cook Islands, the Seychelles and Tonga. The Chinese in particular have been investing in deep sea expeditions to investigate the viability of mining manganese nodules, rocks that contain nickel, copper, cobalt, manganese, gold and also valuable rare earth minerals. This work is being done remotely, however if large-scale operations do go ahead they might be simplified by having people continuously on-site at depth, according to Koblick.

Life aquatic

Then there are those who see underwater living as a way of preserving our species in the event of an apocalyptic catastrophe. In the event of a disaster that put paid to human life, communities could perform reverse versions of Noah's ark. With that in mind, Philip Pauley, a futurist and the founder of the London-based visual communications consultancy Pauley, designed the self-sustaining habitat Sub-Biosphere 2. His design includes circular structures that could be floated out to sea and then sunk, creating a haven for 50 to 100 lucky people.

Building an underwater city is “all I have thought about for the last 20 years,” Pauley says. To raise interest and support, he is pursuing various academic collaborations and is looking for a publisher for the first of a planned science fiction trilogy for young adults he has written called The Moral Order, featuring a dystopian future in which the protagonist discovers a hidden underwater world.

“I don’t want to come across as being fanatical so I am waiting for the right time, when people come around to the idea for themselves,” Pauley says. “When that happens, I will be here with my design.”

Larger underwater colonies are already feasible. What stops them becoming a reality is a lack of interest, motivation and funding. However Polish company Deep Ocean Technology thinks tourism is the way to make the endeavour economical. It has signed deals with architects and builders to deliver the Water Discus Hotel at the Noonu Atoll, Kuredhivaru Island in the Maldives within three years. The company is also involved in discussions about building hotels under the waves in Dubai, Singapore and more than one European location, including in Norway.

“Not many people dive, but underwater life is beautiful and full of all kinds of interesting creatures,” says Pawel Podwojewski, the company’s leading architect. “People may think this is a project meant for just the very rich, but that's not true. In fact it won't be much more expensive than a regular night in a hotel, that's the idea."

Based on having carried out simulations, Podwojewski says it’s cheaper, safer and more efficient to design small steel and glass units that can be submerged and resurfaced using ballast tanks, than attempting to lower large structures to the ocean floor. “We ended up with a similar technology as used in submarines,” he says. “We have plenty of water around to submerge the hotel with, and if we have a problem, we release the water from the tanks and the unit automatically surfaces.”

The Water Discus Hotel will be situated 10 metres underwater in order to optimise sunlight, and will include 22 hotel rooms, a bar and a restaurant with views of the surrounding coral reefs. Prototypes are under construction. In the future, Podwojewski thinks it’s possible that such buildings could help manage overpopulation and serve as models for environmental sustainability, although he doesn't see permanent underwater living as desirable because of the lack of natural sunlight.

Pauley, on the other hand, believes living underwater is a logical solution to the problem of environmental collapse since it would be cheaper and easier to pull off than founding space colonies. “We will have a space colony eventually, but in the near or medium-term the future is going to be living underwater as far as I can see,” he says.

Outside of the realm of science fiction, however, Koblick doubts the life aquatic vision will come to pass. He still hopes that people will come around to the idea of creating new and larger underwater habitats for scientific and educational purposes, but laments that he sees no indication that this will happen within his lifetime. In some ways, he shares Pauley’s sentiments. “I was 27 when I went on my first long, deep dive, and I’m now 74 years old,” he says. “I’ve spent 40-something years trying to unlock the idea of living under the sea.”

Spending more than half his life trying to convince others of the value of longer stays below the waves has convinced him that only a major catastrophe will persuade people to follow his lead. That, or greed. “The only real motivation is if we destroyed the air environment up here and were forced to leave because we couldn’t live in it,” he says. “Or if we started picking up gold nuggets from the bottom. Then it would be done in a heartbeat.”

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