Ocean view

Imagine it is the near future, and life on Earth's surface has become impossible. Rising sea levels have swamped the world's major cities like New York and London and overcrowding and rising property prices are leaving millions without proper homes.

In the recent blockbuster 'Interstellar', mankind had to search for a new home planet in a distant galaxy. However, a Japanese design firm says our future cities will still be on Earth, but deep beneath the ocean waves.

Shimuzu Corp has drawn up plans for an underwater city of 5,000 people that will 'capitalise on all the infinite possibilities of the deep sea'. The company is completely serious and estimates that building it will cost 16bn. The technology to sustain so many lives under water, it says, is only 15 years away.

A group of humans already live underwater: the aquanauts. A university in Florida set up a research station 20m below the ocean's surface in 1993; it can support up to six aquanauts at a time. The station has no doors, as air pressure stops water seeping inside, and it has a hot shower, a kitchen, electricity and even wifi. 'You're inside the aquarium and the fish are watching you,' says one of its occupants.

A marine expert says we already have the technology to support a community of around 100 under the sea and 'if you had the money and the need, you could do it today'. But supporting more people would require more advanced emergency evacuation systems, air supply and humidity controls and a more efficient way to harness energy, perhaps through wave power.

Shimuzu Corp's design includes a research base from which it hopes will find a way to generate energy from the sea bed. This is connected by a spiral path that leads up to a floating sphere which will house the underwater community. But while the city is theoretically possible, would it ever catch on

Some say that while an underwater hotel might entertain those searching for novelty, no right-minded person would want to make an underwater city their permanent address. No one has yet tried to build even a small underwater village, even though the technology exists, so what is going to change? This would only appeal to the super-rich, and it would be an ecological disaster for sea life.

Yet Shimuzu Corp says that while building its first city would be expensive, costs would soon come down as designs become more efficient. And mankind may well need alternative ways to live. By the end of the century sea levels are expected to rise by 2.3m, which may well swamp major cities like New York, Guangzhou and Mumbai. If life on land becomes more difficult, living underwater could be an increasingly attractive idea.