Agriculture has one hell of a footprint, occupying 37.6 percent of earth’s land area, or about 0.7 hectares (1.7 acres) per person to feed our world's current population. “There is no activity that humankind engages in that has a bigger impact on the planet than agriculture,” Jack Bobo, Chief of Biotechnology and Textile Trade in the Department of State's Bureau of Economic and Business Affairs wrote. “This is true in terms of impacts on land and water resources [agriculture accounts for some 70% of our freshwater use (PDF)] as well as in terms of greenhouse gas emissions.”  Dr. Pamela Ronald agrees, “The worst thing for the environment is farming. It doesn’t matter if it is organic [or conventional]…You have to go in and destroy everything.”

We humans have reduced our agricultural footprint; while both the world population and productivity have increased the area devoted to agriculture has decreased. Today's agriculture's land use of 0.7 ha./person is a monumental improvement on the  land needs of  hunter-gatherer societies of about 1000 ha./person.

The increasing agricultural productivity continues. According to Jesse Ausubel, the director of the Program for the Human Environment at Rockefeller University, “From one hectare, an American farmer in 1900 could provide calories or protein for a year for 3 people.” By the turn of the 21st century, the top farmers could feed 80 people for a year from the same area. This has freed up agricultural land. In fact, Ausubel announced last year that the world may have reached (or nearly reached) “peak farmland.”

“Humanity now stands at Peak Farmland, and the 21st century will see release of vast areas of land [PDF], hundreds of millions of hectares," Ausubel writes, "more than twice the area of France for nature.” The trend in the percentage of land in agriculture has been downward over the past five years. How redundant land will be used lies beyond the scope of this post. If it is not needed to grow food or fiber what will the land be converted into? (If in fact we can continue the trend)

Obviously, not needing animals to plow and produce manure, better targeted pesticides, irrigation, bioengineering, and synthetic fertilization of crops have had much to do with increased yields. The tradeoff is more impact on a yet smaller area to keep wild land from conversion to agriculture. But, yes, this system  has meant problems, including runoff from the fields polluting waterways. It is a smaller footprint than it otherwise would have been. “If we were to try to feed the present population of 6.8 billion people using the methods of 1960,"Matt Ridley writes, "we would have to cultivate 82% of the land area of the planet instead of 34%…That would mean ploughing an extra area the size of South America minus Chile.”

Additionally, growing food and fiber where it grows best and trading for other food, fiber, and goods has also lowered the overall footprint. Certain areas have a comparative advantage for growing a specific crop; so the best practice is to grow food and fiber where it grows the best, usually a rural area, and then transport it to an urban area. Why grow bananas in Reykjavik when you can buy them for less from South America? This system of using an area’s comparative advantage for growing and then shipping has been around a long time. The Romans grew much of their food in North Africa and shipped it across the Mediterranean.Today huge container ships which lower the cost per mile of shipping goods have contributed much to the lowering of the carbon footprint.

Could our agricultural footprint be reduced even further?

Columbia University professor Dickson Despommier thinks so. He made his case in 2009 at ScientificAmerican.com, “Because each of us requires a minimum of 1,500 calories a day, civilization will have to cultivate another Brazil’s worth of land—2.1 billion acres—if farming continues to be practiced as it is today. That much new, arable earth simply does not exist.” He quotes Mark Twain: “Buy land. They’re not making it any more.” Additionally, he says, farming pollutes places with “fertilizers, pesticides, herbicides and silt.” He envisions vertical farms in skyscrapers. The Economist magazine wrote about his ideas, “A wide variety of designs for vertical farms have been created by architectural firms. (The idea can arguably be traced back as far as the Hanging Gardens of Babylon, built around 600BC.) So far, however, the idea remains firmly on the drawing board. Would it really work?”

The idea so far works only on a limited basis (without high rises) for niche markets. For example, in Japan, “a plant physiologist,” writes Allison Floyd, “has turned a former Sony semiconductor factory into a farm illuminated by special LED fixtures made by GE. At 25,000 square feet, the farm is nearly half the size of a football field and, since the fixtures emit light at wavelengths that spur plant growth, already is producing 10,000 heads of lettuce per day.” According to “Shigeharu Shimamura, the expert behind the farm…the farm is 100 times more productive for its size than an outdoor growing operation.”

Moving the growing areas of where food and fiber are produced from rural to urban could make redundant some or all arable land currently used for agriculture. The first to move indoors would be the fast-growing, high-value plants. “Obviously, it won’t be apple trees, but arugula, sprouts, basil, cilantro,” Dr. Kevin Folta told Floyd.

The appeal of moving growing food closer to where people live is obvious. As already noted, agriculture occupies nearly 40 percent of the earth’s land area, whereas cities occupy only 0.5 percent [PDF], and now hold more than half of the world’s human population. Demographers expect by the year 2050 that 80% of us will live in cities.

There is a feeling of déjà vu to all of this. “Perhaps the most celebrated past local ‘urban farmers’ were the Parisian maraîchers,” says Pierre Desrochers, co-author of The Locavore’s Dilemma: In Praise of the 10,000-mile Diet. “Through the use of about one-sixth of the city’s area, supporting technologies (from greenhouses to cloches and cold frames) and very long hours, they grew more than 100,000 tons of produce annually in the late 19th century.” They exported some of their produce to London. By the turn of the 20th century however, better transportation able to deliver food and fiber from places better suited to growing coupled with better paying job opportunities for the workers killed their market and made the Parisian truck farm system unsustainable.

Whether we build farms within old factories or stack them vertically, we still need to make the enterprise profitable. Economic sustainability, more than any technological problem, remains the highest hurdle for farming factories.