It takes a big footprint to feed a big world. Today we use land roughly the size of South America to grow food and raise livestock, and that’s just to keep pace with the demands of 7 billion people. So what happens when there are 2 billion more mouths to feed? We can’t expect food to fall from the sky.

Or maybe we can.

Given the potential environmental impacts of putting more land into agriculture—and losing more carbon-storing forest in the process—some experts are advocating alternatives that require less room than traditional methods of growing food. One of the more intriguing ideas is to take advantage of vertical space by stacking greenhouses on top of other structures. These farms-in-the-sky would use soil-free methods such as hydroponics to grow fresh produce, fish and even fruit trees, without the risk of flood or drought or the potential for downstream contamination.

There’s a lot to like about the concept, says Doug Reinemann, a CALS professor of biological systems engineering who studies renewable-energy systems. Greenhouses integrated into urban structures could conserve energy by keeping buildings cooler in the summer and warmer in the winter and mitigate the heat-island effect in urban areas. Nutrient-rich municipal wastewater could be recycled to feed plants. The real payoff, though, would be to put a source of year-round fresh produce in the heart of the city.

“More than half of the people on Earth will be living in highly concentrated urban areas within the next few decades,” says Reinemann. “If we can produce food at the point of use, that could greatly reduce the energy that we currently expend to transport food to where people live.”

True, the amount of food that could be produced in a single rooftop greenhouse is miniscule compared to the output of traditional farms. But ventures such as Eurofresh Farms, a 318-acre greenhouse in the Arizona desert, are beginning to push indoor farming to an industrial scale. And at least one vertical-farming advocate imagines much more: Columbia University professor Dickson Despommier has sketches detailing skyscraper-like farm structures that could grow enough food for 50,000 people in one city block.

Can we get there? It will take some serious advances in engineering and design, says Reinemann. “I wouldn’t even think about trying to explore something like this without expertise in engineering, horticulture and marketing,” he says. “But of course we have those experts (at the university).” And it just may be that the only thing crazier than giving vertical farming a chance is not to.

This article was posted in Agriculture, Cover Story, Economic and Community Development, Features, Food Science, Food Systems, Food Systems, Spring 2010 and tagged Doug Reinemann, features, Fixing our Food, Grow Spring 2010, high-rise greenhouses, indoor farming systems, vertical farming.