"Vertical farming" doesn't stack up.

• Author: Cox, Stan

Agriculture in America has become an ecological, social and nutritional disaster of sufficiently huge scale to inspire a recent frenzy of book-writing, filmmaking, conference-holding and project-initiating. 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 proposed solutions have tended only to nibble at the edges of what is a catastrophe of continental scale.

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, makes the case for what he calls "vertical farming." [1] 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 transport from distant rural farms." (He provides additional details of his vision at verticalfarm.com.)

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: "[L]et us say that each floor of a vertical farm offers four growing seasons, double the plant density, and two layers per floor--a multi plying factor of 16 (4 x 2 x 2). A 30-story building covering one city block could therefore produce 2,400 acres of food (30 stories x 5 acres x 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."

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. [2,3] But even if vertical farming were feasible on a large scale, it would solve no agricultural problems; rather, it would push the dependence of food production on industrial inputs to even greater heights. It would ensure such 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 source of energy to grow and produce.

Nevertheless, modern agriculture has managed to make food production an energy-losing proposition. Its emphasis on increasing yield per unit of land and per unit of human labor has meant a sharp increase in the input of fossil energy--with farms often using more energy to produce the food than is...