By 2025, the world’s population will swell from 6.6 billion to 8 billion people. Climate simulations predict sustained drought for the American Midwest and giant swathes of farmland in Africa and Asia. Is mathematician Thomas Malthus’s 200-year-old prediction, that human growth will one day outpace agriculture, finally coming to pass? Advances in farming technology have kept us fed so far, but the planet’s resources are tapped.
The choice is clear—rethink how we grow food, or starve. Environmental scientist Dickson Despommier of Columbia University and other scientists propose a radical solution: Transplant farms into city skyscrapers. These towers would use soil-free hydroponic farming to slash demand for energy (they’ll be powered by a process that converts sewage into electricity) while producing more food. Farming skyward would also free up farmland for trees, which would help remove carbon dioxide from the atmosphere. Even better, vertical farms would grow food near where it would be eaten, thus cutting not only the cost but the emissions of transportation. If you include emissions from the oil burned to cultivate and ship crops and livestock in addition to, yes, methane from farm-animal flatulence, agriculture churns out nearly 14 percent of the world’s greenhouse-gas emissions.
You can’t buy vertically grown groceries just yet. Most urban farming efforts have been small-scale experiments run in neighborhood parks. Despommier’s vision is bigger: a $200-million, 30-story tower covering an entire city block, stuffed with enough fruit, vegetables and chickens to feed 50,000 people. “With waste in and food out, a vertical farm would be like a perpetual-motion machine that feeds a lot of people,” he says. Most of the technology already exists, he adds, and with some refining, the project could be up and running quickly if granted 0.25 percent of the subsidies paid to American farmers in the past decade—a piddling $500 million.
Despommier is advising investors in Abu Dhabi and South Korea who are considering vertical farms for new eco-cities. Seattle and Las Vegas are investigating similar, smaller concepts. Turn the page to explore the farm of the future, inspired by cutting-edge research from agricultural companies and scientists. With any luck, it will help repel the Malthusian catastrophe for another 200 years.
This automated “conveyor belt” system, conceptualized by
OrganiTech, an Israeli company that creates automated farming systems, takes aquaponics one step further. The tank’s slow current carries floating trays of plants  past nutrient dispensers  and, by the end of the weeks-long trip, the plants are ready for harvest. Below them swim high-protein tilapia , whose ammonia-laden waste sinks to a gravel bed , where bacteria convert it to nitrogen. The system pumps this nitrogen-rich water to the plants, which consume the nitrogen and return clean water to the fish.
But not all plants respond well to hydroponic methods. Some, such as potatoes and citrus trees, need to set root in a semisolid medium, like soil or coconut fiber. The design here, by the Canadian company Omega Garden, does just that. In this Ferris-wheel-like growing system, plants grow in porous, vermiculite-stone-filled trays  arranged in a cylindrical cart  that rotates to periodically dip each row of plants in a nutrient trough .
Five amazing, clean technologies that will set us free, in this month's energy-focused issue. Also: how to build a better bomb detector, the robotic toys that are raising your children, a human catapult, the world's smallest arcade, and much more.