Whole cities built underwater, public transport in airships run on seaweed and farms in skyscrapers—they all sound like crazy ideas dreamed up by science-fiction writers. But they’re in fact real concepts conceived by world-class architects. With concerns about population density, climate change and food availability at the forefront of many urban planners’ minds, architects are starting to come up with imaginative solutions to what the future might hold.

A recent study by scientists at the University of Sheffield found that intensive over-farming in the UK has depleted the soil of the nutrients needed to grow crops. The study estimated that there were only 100 harvests left unless dramatic action is taken, and concluded that we should start to look at our towns and cities as potential farmyards. Growing crops and wildflowers in our cities will not only feed us, but also improve bio-diversity and boost wildlife.

London has approximately 20,000 hectares of roofscape space, so if even half of this was used for food production, the results could be impressive. Belgian architect Vincent Callebaut has taken this idea of bringing the country into the city—he’s come up with designs for “farmscrapers” made from piles of giant glass pebbles for a site in Shenzhen. With the rapid urbanisation of Mainland China, Callebaut wanted to rethink the overall structure of cities and do away with the suburbs altogether.

“The challenge is to create a fertile urbanisation with zero- carbon emissions and positive energy,” he explains. “This means producing more energy than it consumes, in order to reconcile the economical development with the protection of the planet.” These giant stacks of pebbles are intended to house entire communities where all energy would be sourced from the sun and wind, anything produced would be recyclable and local expertise would be used wherever possible. Residents would also work in the towers, reducing the need to travel.

Ideally all food and commodities would be produced within the building, in suspended orchards and vegetable gardens, plus all waste would be fed back in to the ecosystem. The project is called the Asian Cairns. Callebaut’s proposals are for a series of six towers, with some containing as many as 20 giant glazed pebbles. A steel structure would create the curved shapes, while solar panels and wind turbines would be mounted onto the outer surfaces. “Cities are currently responsible for 75 per cent of the worldwide consumption of energy,” Callebaut says. “The contemporary urban model is ultra-energy consuming, and works on the importation of wealth and natural resources on the one hand, and on the exportation of pollution and waste on the other hand. This can be avoided by the creation of green lungs, farmscrapers in vertical storeys, and the implantation of wind and solar-power stations. The production sites of food and energy resources will be reintegrated into the heart of the consumption sites.”

While Callebaut advocates reducing the spread of cities, some architects are taking this a step further—either by going on or under the water, or reaching for the sky. Also in Mainland China, proposals have been submitted for the creation of a “floating city” off the coast, complete with underwater chambers and a self-contained ecosystem. The four-square-mile urban centre aims to provide housing for residents of China’s overcrowded cities, but would also serve as a high-end tourist attraction with restaurants, hotels, bars, museums, galleries and theme parks, both on and below the water’s surface. Satellite farms would grow food, hydropower generators would provide energy, and rainwater from roofs and facades would be channelled into a freshwater lake. With rising sea levels a major concern, this proposal is one to be taken seriously.

A cinematic concept for an Australian “city of the future” was put forward by Melbourne- based John Wardle Architects, as a contribution to the Now and When Australian Urbanism exhibition at the 2010 Venice Architecture Biennale. The architects created Multiplicity to address the issues of climate change, population growth, sustainable resources, ecological systems and technological advances. The firm’s idea was to grow up, not out, from Melbourne’s city centre. So the architects conceived a giant platform, which is suspended by pylons between buildings above the city, offering a space to grow food and provide shade to protect residents from rising temperatures in the coming years.

While it may sound somewhat fantastical, Multiplicity was inspired by the real problems that city planners face when predicting the future. However, a lot of these thrilling projects never make it off the drawing board. For example, Archipelago 21, a master plan for the sustainable redevelopment of the Yongsan International Business District of Seoul— designed by Studio Daniel Libeskind, the architect of the new World Trade Centre in New York—has been put on hold for the time being. Notable completed projects, where the environmental cost is as important as the impact of the building on the viewer, include several by Chris Wilkinson and Jim Eyre, directors of Wilkinson Eyre Architects, a UK-based practice at the forefront of design for the cities of the future. The firm was behind the 438-metre-high Guangzhou International Finance Centre. The tower’s diamond-shaped structure, exposed throughout the offices, atrium and hotel inside, looks simple but is hugely complex. It not only allows the dramatic tapering atrium and raked floors, but also brings environmental benefits by using 20 per cent less steel than similar buildings.

Wilkinson remains positive about the future and our attempts to cope with it. “I’m a great believer in science and technology. We have to remain focused on developing technological solutions to deliver the best, for the most, in a sustainable way,” he says. “I believe that we are on the trail of clean energy sources and techniques to repair some of the damage done to the planet, and it’s encouraging to see entrepreneurs such as Elon Musk, the co-founder of PayPal, placing big bets on sustainable technologies.” As the cities of the future become more densely populated, they will probably require taller buildings—and are likely to house a mix of uses rather than a single function. Wilkinson also addresses the problems of traffic congestion and pollution that affect most of the metropolises in Asia.

“Buildings will be better integrated, with connections running between them on the upper levels,” says Wilkinson. ”I think there will be more streets at different levels because the ground level will become too congested. Moving pavements on connecting bridges will provide shortcuts from offices to social interaction spaces and apartments.

”Wilkinson Eyre Architects also worked in Singapore on Gardens by the Bay, a carbon- neutral botanical garden recognised by the Guinness World Records as the largest glass greenhouse in the world. It’s an important part of a long-term national government strategy to secure Singapore’s future by reimagining it as “a city in a garden.” The Gardens provide a starting point for developments on reclaimed land, and are planned as a leisure-activity area for residents as well as a tourist attraction. With 10 million visitors to date, this strategy seems to be working well. “The Gardens are the centrepiece of a nationwide greening strategy that will improve the quality of life for all Singaporeans,” says Wilkinson. “The overall strategy tackles major problems such as water security—the gardens are built on reclaimed land that was used to enclose a freshwater lagoon, which will supply the city with water.”

So with a little innovation from architects and designers, coupled with the support and long-term visions of governments, the future isn’t looking too bleak. “It’s clearly not desirable to impose restrictions on energy consumption, so the only option is to find cleaner energy sources and more energy-efficient technologies,” says Wilkinson. “I think it might be possible to tap into the oceans, and possibly the earth’s core, as a future source of energy.” Perhaps the idea of an underwater city isn’t that far-fetched after all.