As coastal cities face growing threats from rising sea levels and urban planners debate where to build next, a Japanese company has an unconventional proposal: Maybe the cities of the future should be built underwater.
The Ocean Spiral, a futuristic concept for a self-sufficient city designed to float in the middle of the ocean, uses the sea to run infrastructure that could support 5,000 people.
A giant sphere, 500 meters in diameter, would hold a tower with hundreds of apartments and larger homes, stores, offices, a hotel, and research facilities, all descending 75 stories down into the water. A seawall would circle the sphere, keeping large waves away, while tethers and ballasts keep the city from drifting in the water.
Though building underwater poses obvious challenges, the company behind the development believes that it also could have multiple advantages for the environment.
“The deep sea contains enormous possibilities that can possibly help ongoing environmental problems throughout the world,” says Hideo Imamura, a spokesperson for Shimizu Corporation, the company working on the design. In theory, underwater cities could help relieve pressure for more power, food, and water on land, while providing a new place to store carbon dioxide.
The city could automatically generate all of the energy it needs, using the temperature difference between surface water and the deep sea to make thermal power. A long spiraling tube would travel nine miles down to the sea floor, pulling cold water up for the city’s power plant.
Using some of that same energy, the city would also run a desalination system to provide unlimited freshwater for the people living there. As agriculture on land struggles to feed growing populations, the city would rely on its own aquaculture farm–essentially a giant, partially enclosed aquarium for raising fish–near the bottom of the sphere.
To help address climate change, the city would send carbon pollution from power plants and other land-based sources down to the sea floor, where microorganisms would convert it to methane gas. The company also envisions harvesting new resources from the sea floor–but rather than mining, new systems might mimic natural processes to begin automatically growing and harvesting new minerals.
As fantastical as it might sound, the company believes it’s feasible, and has been working on the details with experts from Japanese universities and national agencies. One of the biggest challenges, the company says, will be figuring out how to build the city–the construction of the concrete sphere will happen in the water, using a huge 3-D printer. If it’s built, the city is projected to cost around $26 billion.