What’s for dinner? For that matter, what’s to eat, full stop? In a few decades time, that second question may become pressing. Mankind’s awareness of our food supplies has been heightened by massive crop failures due to millennial level floods, protracted droughts, and numerous food-borne disease outbreaks caused by microbes such as salmonella,E. coli strain 0157, toxoplasma and listeria. Consumers the world over now demand to know where their food comes from and how it is produced.

As if that were not enough to keep us up at all hours of the night, larger issues loom in the near future as our population continues to expand, placing greater pressure on the world’s agricultural industries to meet demands. As a species, we need to know whether modern farming is sustainable and compatible with the rest of the natural world, or is it causing irreparable damage to the environment that will eventually turn today’s serious problem of today into a food crisis of epic proportions in the near future?

To answer some of these questions, it’s important to recall how things got this way to begin with. In the beginning of the modern era of humankind, around 10,000 years ago, most of our earliest cities were located close to agricultural land. Cities needed crops.

In the Middle East, for example, einkorn wheat was first successfully cultivated around 11,000 years ago in the south-eastern part of what is now Turkey. Farming then rapidly spread through the whole of that region. It had many advantages, including the fact that when wheat yields exceeded demand, its grain could be stored without losing any nutritional value. These early cities – Ur, Nineveh, Jericho, Babylon – became established next to their farmland, and for a time flourished in concert with the fields that provided their sustenance. Yet despite the invention of farming, eventually all of these early cities fell into disrepair, their decaying fortified walls and crumbling buildings blending seamlessly back into the harsh, arid landscapes which gave rise to them. The cause? Desertification. Drier weather patterns caused the failure of this single crop their civilisation depended upon – a mono-crop dependent upon a constant source of water to survive. It was irrigation which allowed such large amounts of wheat to be grown – but falling water levels brought the Middle East’s first agricultural revolution to an end. Only Egypt survived in the long term, thanks to the Nile River.

Today’s cities are at risk from a different set of issues. If trends in urbanisation continue at their current rates, cities could evolve into places where intolerable numbers of people may have to live, and who are forced to live well below the poverty limit, threatening to overwhelm sanitation systems and housing. Food and drinking water would be even scarcer than in many of today’s developing cities.

But this doesn’t have to happen. Most urban centres are experiencing a re-birth of their direct connections to agriculture. Within just the past 10 years, an increasing interest in city farming has been paralleled by the creation of the slow food and locallly sourced, or “locavore” movements, a foundation for the rise of urban farming initiatives.

Bright lights, big city

Included in the mix of successful city-based agricultural projects are rooftop gardens, rooftop greenhouses (both low tech and hydroponic), above-ground planting beds, the use of empty lots as farmland, and vertical farms that occupy tall buildings and abandoned warehouses. Collectively, these examples show the validity of growing food in the city. Not only could be they be carried out efficiently – such as rooftop greenhouses giving much higher yields than outdoor farms – but they could also operate without the pollution associated with outdoor farming.

Already, we have large-scale indoor farms such as EuroFresh Farms in Willcox, Arizona (318 acres (1.3 square km) of one-storey-high hydroponic greenhouses), supplying fresh tomatoes and cucumbers, andFarmedHere in Bedford Park, Illinois, a 90,000 square-foot (8,360 square metre) empty warehouse several storeys tall that was converted into an indoor farm producing tilapia (freshwater fish), a variety of leafy green vegetables, and several value-added products. Indoor farms (controlled environment agriculture or CEA) will undoubtedly replace most outdoor urban agricultural initiatives as the advantages of farming within protected environments become more widely accepted.

Judging by current trends in the development of advanced technologies, city-based CEA appears to have a bright future, as newer strategies emerge enabling indoor farming to be carried with increasing efficiency. Grow lights, for instance, have evolved from ordinary fluorescent light fixtures – expensive to operate – into a series of light-emitting diode (LED) lighting schemes. These LED lights can be adapted to emit light spectra at two dominant wavelengths (red 680nm; blue 460nm) tailored for growing green plants. The benefits of LED grow lights are obvious when compared to other outdated lighting schemes: LEDs cost less to run, and produce greater yields of most commercial crops, such as leafy greens and tomatoes. In early 2013, Phillips in the Netherlands announced it had invented an LED light with energy efficiency 150% greater than existing LED grow lights. This new development promises to significantly reduce energy costs involved in growing such crops.

Although most current vertical farming operations have chosen to specialise in cash crops consisting of leafy green vegetables (easy to grow and much in demand), in the near future, consumers are likely to ask for a wider variety of vegetables and fruits grown without pesticides, herbicides and other harmful chemical contaminants. At that point, vertical farming in tall buildings will replace less productive single-story greenhouses as the source of all city-grown produce. Some form of vertical farming now exists in Japan, Korea, Singapore, the United States, and Canada. New vertical farms are planned for a number of cities in the United States (Milwaukee, Memphis and Jackson Hole in Wyoming), andLinköping, Sweden.

Urban agriculture has the potential to become so pervasive within our cities that by the year 2050 they may be able to provide its citizens with up to 50% of the food they consume. In doing so, ecosystems that were fragmented in favour of farmland could be allowed to regain most of their ecological functions, creating a much healthier planet for all creatures great and small.

The 1995 film Waterworld was one of Hollywood’s most infamous budget busters – a mega-million-dollar post-apocalyptic thriller that, at the time, cost more than any other film ever made. It did a pretty decent job of sinking Kevin Costner’s career for the rest of the decade. More importantly, it may also have helped do the same to the idea of mankind living on the sea.

Though scientists aren’t predicting sea-level rises of the magnitude seen in Waterworld – hundreds of feet thanks to melting polar ice caps – we may have to plan for a world with much higher sea levels. There has long been a dream that one day mankind, or at least some of us, will live on the ocean. Designer and architect Buckminster Fuller saw cities at sea contributing to a sustainable future for humanity. But then floating cities evoked images of flop films, or worse, of wealthy “robber barons” escaping to the high seas for financial reasons. Now, several groups are trying to change this perception by researching technologies that could help create floating cities, or “seasteads”, which become innovative models of sustainability and peaceful cooperation.

Does this sound too futuristic? Then consider China’s Fujian Province,where the Tanka people have been settled at sea since 700AD. Pushed into coastal waters in wartime during the Tang Dynasty, these boat dwellers weren’t allowed to set foot on land until the second half of the 20th Century. Today, some 7,000 Tankas still maintain a sea farming life – possibly a preview of a future to come for many more of us. Before the industrialisation of agriculture, most people lived in land-based villages no larger or more complex than the Tankas’ simple water-based community. It took a series of green revolutions in farming technology to allow people to leave rural communities, and move into densely-populated urban areas. We see signs that a “blue revolution” in ocean harvesting technology is underway, suggesting floating cities can’t be far off.

Supply issues

It may be a necessity – not merely a novelty – to inhabit the sea in the coming decades, but to do so will require the means to create reliable and sustainable food and power souces. Dwindling fish stocks from overfishing have prompted humanity to create farmed supplies, beginning with the most accessible environments on or near land. Yet most fish farming has not evolved beyond the low-tech cages and seaweed-draped lines anchored in shallow seas by ancient peoples like the Tankas. The most advanced methods of mass production employ harmful antibiotics and genetically modified feed in unnaturally crowded ponds on land.

But the drawbacks of current fish farming has created opportunities for technology like the floating “drifter pens” pioneered by Kampachi Farms. Given enough time, Kampachi Farms will replace stagnant ponds with GPS-tracked cages stitched out of copper wire to enable a constant inflow of fresh ocean water without flushing out the precious fish. These geodesic aquariums, inspired by Fuller’s prototypes for sturdy light-weight structures, will be let loose in swirling ocean gyres, where they only need occasional course-correction to maintain a rough position. This will be accomplished by nimble harvesting vessels driven by pioneers of this new life on the water.

Collapsing fisheries are of immediate concern, but land-based agriculture may also be in danger due to a predicted shortage of the crucial nutrientphosphorus by the year 2050. Once again, there could be a solution out at sea.

Blue Revolution Hawaii, led by Professor Patrick Takahashi, is another group planning for a future with thousands of floating cities. Takahashi and his team have devised a plan to enable large ships equipped with ocean thermal electric conversion, or Otec plants, in which warm surface waters interact with cold water “upwelled” from the deep ocean to drive a large power turbine. The cool water pumped to the surface contains the exact ratio of nutrients – including phosphorus – needed to support plant growth.

Otec technology has already been tested in Hawaii, and China’sReignwood group recently announced plans to complete a 10 megawatt plant – the first on the open-ocean – not far from the Fujian Province in China’s southern seas. Living space may be cramped at first, but the abundant sunlight and acres surrounding these pods will be enough to feed vast ocean ranches, supercharged by Otec’s nutrient-rich byproduct. At the bottom of this food chain, algae will feed fish, which feed bigger fish, which will in turn feed seafarers and land-lubbers alike. Sinking fish waste and seaweed detritus will gradually sequester carbon dioxide from the atmosphere and deposit it on the seafloor to restart nature’s eons-long process of creating fossil fuels. By 2050, it’s not far-fetched to imagine hundreds of these plants grazing the high seas, trading abundant seafood surpluses with cities on land.

Meanwhile, Shell is preparing to anchor the world’s largest floating offshore structure – the Prelude Floating Liquefied Natural Gas facility – off Australia’s north-west coast in 2014. The structure will be massive – the length of four football fields and one field wide. It will be built to withstand Category Five typhoons, and will produce the natural gas equivalent of 100,000 barrels of oil per day. While few groups could afford to build a floating city capable of weathering such storms, Shell’s example demonstrates the long-lived feasibility of living on the sea. In fact, most fundamental challenges of living safely on the ocean have been solved by offshore drilling or shipping companies (cruise lines got satellite internet years ago, while most of Asia and Africa still lack it). Costs will fall over time. And what is Shell going to do with Prelude once all the natural gas runs out?  The infrastructure for a marine community will be waiting to be used.

Free floating

The Seasteading Institute has also been dealing with the challenges faced by communities trying to live permanently on the ocean. It is an audacious but essentially pragmatic endeavour. Taking a cue from the Tanka people, the plan is locate in the protected, territorial waters of a nation willing to “host” the structures and their inhabitants. With help from the Dutch aquatic architecture firm DeltaSync, the institute hopes to design something that will meet the needs of residents, and the host nation. From a calm coastal area, the logistical challenges needed allow a community to live on the high seas can be solved one at a time.

British designer Phil Pauley has developed a concept for a sea habitatcomprising interconnected spherical modules that could submerge during storms and rest at the surface in good weather. The long vertical trusses holding up Pauley’s design use Fuller’s principles for strong, lightweight “tensegrity” structures. They maximise support without using too much expensive material such as steel. To reach much deeper waters, communities will ditch the stilts and float freely or anchor.

Others are trying investigating this technique on a smaller scale too. Do-it-yourself sea-living enthusiast Vince Cate has been using prototyping simple “ball stead” homes, which achieve buoyancy and stable surface “real estate.” Testing models in the Caribbean Sea, near his home in Anguilla, Cate has found that suspending a heavy weight well below the surface keeps the ball from moving amid the waves.

And these structures could last for a very long time indeed. Simple cement structures, reinforced with steel, can displace massive amounts of water, and last for decades – or even centuries. Even after 2,000 years of the sea’s harsh beating, a Roman harbour built with a mixture of standard concrete and volcanic ash is still intact. Electro-accretion – essentially sticking concrete-like minerals on galvanized underwater structures – means electrified steel mesh could eventually be used to reinforce and repair underwater concrete structures.

The first floating city is expected to take to the water around 2020. We are already researching ways to harvest food and energy in deeper, more remote parts of the ocean. Future cities built from scratch will be more dynamic, energy-efficient and flexible. These cities of the sea could use algal biofuel production and store energy from wind and the Sun. As designs improve – and get cheaper – the idea of a home on the ocean will become more affordable.

Does all of this sound crazy? In a sense, it is. But some would prefer to be called crazy than to pretend our cities and species can keep going with the status quo.