Light, seeds, soil, and water. The recipe for growing food out of the ground is among the planet’s simplest equations. Tweak the variables—less light, different dirt—and you can grow anything from feathery lettuce that’s lighter than air to a beefy jackfruit, the world’s densest fruit, which can weigh more than a hundred pounds.

So it’s strange that in the middle of the day on a recent Thursday we’re walking through a dark tunnel on the way to a farm. The facility is a hundred feet below the streets of London, 179 steps down, in an old air-raid shelter built in 1944 for protection from German bombs. During the blitz more than 6,000 people huddled shoulder to shoulder in this small tunnel. Today the only overnight occupants are a few green shoots of radish, celery, and spinach. They’re prodded to grow by a simple aquaponics system where water circulates through a series of trays that hold the crops. There’s no soil, only old carpet from renovated hotel rooms. LED lights powered by wind turbines on the surface emit a light pink hue, the precise mix of ultraviolet and infrared light that the plants need. Anything extra would be wasted energy.

Underground Farming in a London Bomb Shelter

“We don’t know entirely what to expect,” says Steve Dring while we’re walking through the dark tunnel. Dring, along with his business partner, Richard Ballard, came up with the idea last year to build a farm underground, away from a natural source of water and far removed from the sun. Rent for the space was cheap as long as they could live with a few small water leaks in the 70-year-old tunnels. No one else was using the facility (a night club was turned away because there weren’t enough exits). Once Dring and Ballard had gotten a lease to grow crops, their lawyer admitted that he was curious about what the two men might actually grow in a dark, private space using artificial lights.

The novelty of an underground farm that grows spinach and garnish herbs for high-end salads isn’t lost on them. They know farming underground isn’t the key to feeding a global population. But the quirkiness of the idea could provoke questions about what tomorrow’s farms might look like. It also makes for good PR and fund-raising: Virtually every tech-news outlet has come asking for a tour, hoping to provoke its readers with a shocking headline about whether growing underground is the future of global agriculture.

View Images Who needs sun? Steve Dring and Richard Ballard grow salad greens with reclaimed water and lights powered by wind turbines.

Of course it’s not. News of an underground farm in London isn’t enough to make corn farmers in Nebraska and rice growers in Indonesia lay down their hoes in defeat. Even earth powered by the most highly phosphorous fertilizer and the brightest lightbulb couldn’t compete with the rich soil of a Napa Valley or the well-watered farmland of Congo or Argentina.

Instead the notion is a gesture of ingenuity, a token approach very much outside the box to how our species might grow more food for an increasing population on a planet of limited size. “We’re not planning to take over traditional farming,” Steve Dring says. “But we are trying to confront the idea that we’re running out of land and need to find new places to produce food.”

Arable farmland—the expanse of Earth that can be used to grow crops—can be a funny thing to measure. Land, like people, comes in different shapes. It also changes over time, formed by a quick deluge or a long, punishing drought. When abused, it’s easily exhausted. There’s no such thing as land that stays prime forever.

To understand how much space on Earth is suitable for farming, imagine the globe as an apple, and slice it into four wedges. Three of the wedges represent Earth’s bodies of water, and are disqualified for growing crops. Of the remaining wedge, half represents land unwelcoming to agriculture, in deserts or near the frigid Poles. The rest of the apple (one-eighth of the planet) represents land where food could grow—except that three-fourths of it has been paved over by cities and roads and other human civilization. All that’s left is one-fourth of that last wedge, or one thirty-second of the surface of the Earth.

View Images Drawing by Spencer Millsap

That amounts to 57 million square miles of farmland globally. Splitting the land among the world’s 7.1 billion people would give each person alive about five acres. That’s more than enough to raise livestock and grow a rounded diet of fruits and vegetables.

Yet that land is highly disproportionate. Some 90 percent is located in Latin America and sub-Saharan Africa. Half is concentrated in just seven countries: Angola, Argentina, Bolivia, Brazil, Colombia, Congo, and Sudan. Areas with notably booming populations—like China and Qatar—have the least available farmland per capita of anywhere on Earth. This pushes them to buy land abroad, especially in Ukraine and Morocco, which have large expanses of usable land and hearty reserves of phosphorus—the main ingredient in fertilizer.

All together, that area of land produces about four billion tons of crops every year. Yet not all food is equal. More than half the crops grown every year become rice or grain. Potatoes are the single most eaten vegetable, followed by tomatoes, cassavas, and oranges.

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For now the system is mostly stable. Despite beauty queens’ best efforts to end hunger, people continue to go hungry. Yet the world actually produces a surplus of calories every year. “Hunger is caused by poverty and inequality, not scarcity,” Eric Holt Giménez, director of the Institute for Food and Development Policy, wrote last year. “For the past two decades, the rate of global food production has increased faster than the rate of global population growth.” Instead, feeding the poor corners of the world as well as the 70 million new mouths being born every year will mean farming smarter and on less land—even occasionally in dark tunnels.

Yet a few expectations for the future add urgency. One of the most pressing concerns, laments Berkeley economist David Zilberman, is that one billion people currently “eat like Westerners,” meaning they have diets high in meat and dairy that take longer and are costlier to produce. Never mind that a few billion more people will soon be born. Billions of people already alive have ambitions to upscale their diets.

View Images New celery, radish, and mustard shoots are ready to be harvested once a month.

Somehow the market is expected to work, but not seamlessly. The price of food is expected to rise 2 to 3 percent each year, which is expected to encourage more production, which is expected to encourage more development over wetlands and forests. Faced with the reality that the majority of the world’s industrial farmers are over 50 and will soon retire (the average U.S. farmer is 57), farming will have to become a more attractive proposition to draw younger people. The ultimate impact is likely to be food prices that rise faster than inflation. “It’s a heck of a big problem,” says Andrew McElwaine, president of American Farmland Trust, the advocacy group that pioneered the imagine-the-apple-as-the-Earth metaphor. “There is a sense of urgency because of this convergence of growing population and limited availability of arable land. When those lines cross, it won’t be pretty.”

View Images Clay pellets are used to simulate flooding for crops like potatoes and carrots with deeper root systems.

But it’s not entirely inevitable. The saving grace is innovation, the marketing term for producing more food from less land. Until about 1940 yields of most crops in the United States were consistent every year and proportional to the amount of land they were grown on. The introduction of nitrogen fertilizer, genetically optimized seeds, and mechanical plowing methods has produced yields that would make a Neanderthal’s head explode in envy. Since 1960 yields have doubled, or even tripled, everywhere in the world except Africa, while most land for farming has increased by only 10 percent.

Last December a modest farmer in Charles City, Virginia, named Dave Hula won an agricultural award that demonstrated the leaps made by modern humans. Using seeds engineered to produce voluminous yields with minimal input of fertilizer and water, Hula grew 454 bushels of corn on one acre. Compared with the industrial norm of about 125 bushels, Hula had farmed the most productive acre in human history.

Not everyone has the power or know-how to grow food. That might be the ethos of modern industrial farming, in which large corporations and the sprawling farms that buy their seed and fertilizer produce a growing amount of the world’s nutrition. (Disclaimer: one of those companies, Syngenta, has purchased advertising with National Geographic.)

As large-scale food production has grown, one counterbalance has been the concept of food miles. Learning how far tomatoes or frozen chicken need to travel to reach supermarket shelves brings awareness about environmental impact. From California, which grows more than three-quarters of most of America’s fruits and vegetables, to a supermarket in Washington, D.C., produce trucks carry spinach, garlic, and blueberries the width of the entire continent in usually less than a week. Each truck can burn over 500 gallons of diesel along the way.

That guilt-inducing fuel consumption, as well as a rise in locavore thinking, has been the driving force behind decentralized farming. The idea of buying food from someone who grew it nearby came back into vogue in the mid-1990s. During the first term of the Clinton Administration, there were 1,700 registered farmers markets in the United States. Today the number has more than quadrupled.

“The trend is very clear,” says Nicholas Leschke. Like the men in London with the tunnel idea, Leschke is part of a two-man team of entrepreneurs—not farmers—trying to imagine the future of urban farming. “People want food that’s high quality—produced locally and very efficiently.”

View Images NG Maps

Maybe they do. Certainly some people just care that there’s food on the shelf when they go to buy it, no matter where it was actually grown. But Leschke is banking on a future where people not only want local food but also want to be able to reliably grow it themselves. In an old industrial parking lot in Berlin, he and his business partner developed a farm out of a repurposed shipping container—called, in the spirit of German directness, a “container farm”—that produces both fish and fresh crops.

The container farm runs an aquaponics loop, where fish swim on the first level, and fresh vegetables like tomatoes, peppers, and potatoes grow in the greenhouse above. The fish waste is used to fertilize the plants. The plants help purify the water and return it to the fish below. When the farm expands later this year, the developers expect it to produce 6,000 tons of fresh fish—raised locally and with minimal input.

In theory a hundred years from now, every family’s roof could have a farm to grow vegetables, fruits, fish, and even meat from just a few cells in a petri dish. But aside from people who farm in London tunnels or on Beijing rooftops or who attend meetings at a Brooklyn food co-op, there's the pesky question of whether that’s really the most efficient way to produce food for billions of people. And is tending their own rooftop farm what future people in their Jetsons-style flying cars and smart houses will want?

View Images Nicholas Leschke wants to use aquaponics to raise tilapia in small, dark tanks.

The answer might be the best indication of where future food will actually be grown—and more important, who will grow it and on how much land. One running joke among farmers is that a lot of people like to garden, but very few like to farm. Eating tomatoes you grew yourself is worthwhile, but it isn’t scalable for the planet, says Jesse Ausubel, an ecologist and food analyst at Rockefeller University in New York.

The day I talked to Ausubel, I was working through lunch. In front of me was a turkey sandwich made with meat produced on a factory farm, accompanied by a bottle of juice squeezed from oranges grown in both Brazil and Florida. As much as I think and write about food, I was eating one of the most generic American lunches, created by farmers who have demands to keep up with rising appetites—and who, based on how easy it was for me to buy each item, seemed to be succeeding.

Food, Ausubel told me, is a little like clothing. “There are large companies that turn out the blue jeans and T-shirts we all wear. We don't mind large scale for that. But sometimes we all want a little something nicer, a little more fashionable. Even people without much money want something of their own or something they made themselves. Character matters, so does a sense of ownership. It's the same story with food.”