Several groups are already working toward underwater cities within the next 15 years – if not sooner, depending on how you define underwater cities.

It’s only a matter of time until people are living underwater… right? If science fiction has taught us anything, it’s that sooner or later people will be living in underwater cities. And have robots for work around the house. And jetpacks.

Sure, there are plenty of good reasons for bold humans to live under the seas like rising sea levels and massive overcrowding in urban centers, but there is one reason that overrides them all: underwater cities are cool. And if one Japanese company has its way, the first bottom-of-the-ocean dwellers may begin to challenge even the best delivery services by 2030, or sooner.

Underwater Cities May be a Reality in 2030 – If Not SoonerThe Japanese construction company Shimizu Corp recently announced plans for a $25 billion underwater city, known as the “Ocean Spiral.” The city would house around 5,000 people, and be almost entirely self-sustaining. Current levels of technology aren’t quite there yet, but the Japanese firm believes that the necessary construction technology will be available by 2030, if not sooner.

The Ocean Spiral will consist of three separate sections, with two-thirds below the water. The first section will float on the surface, and feature a 500-meter sphere. Ships will presumably be able to dock there, helicopters will be able to land in the sphere, and there may even be a floating runway for planes.

The second section will be the largest section, where the majority of people would live. This section would be entirely underwater, and contain the commercial and residential units. There would probably be some forms of gardens and parks as well – having a little greenery to counterbalance the darkness of the ocean would be important, plus the vegetation would help with creating oxygen and scrubbing carbon dioxide.

The third section would be the most ambitious and feature the “earth-factory,” a research center for developing energy sources. The bulk of the bottom section would be between 3,000 to 4,000 meters deep and in total, the structure would be nearly 10 miles long, with most of the structure buried deep into the sea floor.

According to Shimizu, there are several research firms and groups supporting the endeavor. The group is also looking to secure funding from both private groups and governments.

Underwater Cities May be a Reality in 2030 – If Not SoonerPart of the attraction would be the Ocean Spiral’s ability to be self-sufficient. There would be sections dedicated to farming and livestock, the city would generate energy through several different means, and both solar power and hydroelectricity could be utilized. Another intriguing idea would be to produce methane from carbon dioxide using organisms, which would help scrub the enclosed atmosphere while creating a natural gas resource. The different ocean temperatures could also help to generate power through thermal energy conversion.

And while the Ocean Spiral is one of the more fully realized projects, it is not the only underwater city in the works.

The British/Asian design firm, AT Design, was commissioned by the Chinese construction firm CCCC to consider ways to live like Aquaman. Unlike the Ocean Spiral, AT Design’s underwater city would be only partially submerged, with the city spanning nearly four square miles above and below the water. Below the surface, transparent tunnels would connect the structures together and offer vertical gardens, commercial and residential areas, and farms. As with the Ocean Spiral, the goal would be to make the city completely self-sustaining.

Perhaps the most ambitious of the underwater cities currently being considered is a concept from Belgian architect Vincent Callebaut.  He recently unveiled plans for a series of submerged “eco-villages” known as the “Aequorea,” which could house up to 20,000 people. His idea is to create “oceanscrapers,” giant structures that stretch thousands of feet from the seabed to the surface, capped with a small, domed section resting above the waterline.

Callebaut’s proposal is still years away from being realistic, but the plan is to build the structures using recycled plastics. The Aequorea would house commercial and residential units, research labs, farms, and entertainment areas. Each structure would be an estimated 250 floors, reaching a depth of 1,000 meters. Buildings would be self-sufficient, with desalinization centers creating drinking water from seawater, microalgae to recycle organic waste, and light generated by bioluminescence.

As with the Ocean Spiral, the biggest concern – or one of the many major concerns – is the pressure found at these depths. We have the technology to travel thousands of feet below the surface, but any structures down that deep would need countless redundancies. Even the smallest crack could be disastrous.

In many ways, living beneath the sea would be similar to living in space, just with gravity. Even with gardens and all the comforts of traditional city living, it would be an inhospitable location. But with sea levels rising and population centers constantly looking for new ways to expand, underwater cities may be the next logical progression.

Construction companies and designers are always considering new ways to maximize space and take advantage of new locations. Some are floating on the water, some are far above it orbiting in a low-Earth orbit. Wherever we end up, the future is going to be cool.