Why Planting Farms in Skyscrapers Won't Solve Our Food Problems

Agriculture in America has become an ecological, social and nutritional disaster of sufficiently huge scale to inspire a frenzy of book-writing, filmmaking, conference-holding and project-initiating in recent years. The critiques that emerge are often right on the money, highlighting pesticide and nitrate pollution, soil erosion, the consequences of meat production in feedlots and confinement sheds, the destruction of rural communities and the poor nutritional quality of food. But the solutions being proposed have not, for the most part, been of the same scale as the problems; most would do little more than nibble at the edges of America's long-running agricultural fiasco.

A striking example of such ill fit between problem and proposed response can be found in the November 2009 issue of Scientific American, where Dickson Despommier, a professor of public health and environmental health sciences at Columbia University, made his case for what he calls "vertical farms," a vision he promotes through his site verticalfarm.com.

After doing a very good job of describing the terrible toll that agriculture takes on soil, water, and biodiversity across the globe, Despommier's article lays out a proposal to replace soil-based farming with a system of producing food crops in tall urban buildings-to, he writes, "grow crops indoors, under rigorously controlled conditions, in vertical farms. Plants grown in high-rise buildings erected on now vacant city lots and in large, multistory rooftop greenhouses could produce food year-round using significantly less water, producing little waste, with less risk of infectious diseases, and no need for fossil-fueled machinery or trans¬port from distant rural farms."

Despommier describes how one of his scenarios-which are based on the use of hydroponic or "aeroponic" methods of growing plants without soil-might work: "Let us say that each floor of a vertical farm offers four growing seasons, double the plant density, and two layers per floor-a multiplying factor of 16 (4 _ 2 _ 2). A 30-story building covering one city block could therefore produce 2,400 acres of food (30 stories _ 5 acres _ 16) a year." By extrapolating numbers like those and assuming extraordinary leaps in technology, as well as the repeal of Murphy's Law, he has made such a convincing case for vertical farms that, he claims, "many developers, investors, mayors and city planners have become advocates." Time magazine has run a generally positive story on the concept. And an Australian architect is currently planning to build the first full-scale vertical farm, in China.

The idea for vertical agriculture grows out of the realization that there are not enough exposed horizontal surfaces available in most urban areas to produce the quantities of food needed to feed urban populations. Although the concept has provided opportunities for architecture students and others to create innovative, sometimes beautiful building designs, it holds little practical potential for providing food. Even if vertical farming were feasible on a large scale, it would not solve the most pressing agricultural problems; rather, it would push the dependence of food production on industrial inputs to even greater heights. It would ensure that dependence by depriving crops not only of soil but also of the most plentiful and ecologically benign energy source of all: sunlight.

Groping in the dark

Agriculture as it has always been practiced-call it "horizontal farming"-casts an extremely broad, green "net" across the landscape to capture solar energy, which plants use in producing food. Photosynthesis converts a small percentage of the solar energy that falls on a leaf into the chemical energy in food. But that small percentage is enough; sunlight is plentiful, and left to themselves, plants do not have to rely on any other sources of energy to grow and produce.