When I was in college (Class of ‘62), I encountered something that only had negative connotations: circular reasoning. Wikipedia defines this kind of fuzzy logic thusly:

Circular reasoning (Latin: circulus in probando, “circle in proving”; also known as circular logic) is a logical fallacy in which the reasoner begins with what they are trying to end with. The components of a circular argument are often logically valid because if the premises are true, the conclusion must be true.

The first time I heard the term I was understandably confused, as were many of my classmates. Eventually we got it, and resolved to think more rigorously (at least during class). Since those formative years, four billion more people have arrived on this planet, and along with them rapid climate change with its portent of an apocalyptic future. I am now a practicing urban ecologist, advocating for the establishment of high-rise buildings within the city limits that produce significant quantities of vegetables, fruits, and herbs. It is called vertical farming (VF). The concept arose in 1999 in a course I taught, and miraculously that idea has become a reality. Hundreds of VFs currently exist, with most of them located in Japan, Singapore, China, Europe, and the United States. Many VFs were created simply by retrofitting abandoned buildings (e.g., warehouses, factories), while others were built from scratch. Most of them employ some form of hydroponics or aeroponics technology as their growing system of choice. A few use soil-based methods. All of them owe an enormous debt of gratitude to the high-tech greenhouse industry that pioneered indoor farming, starting in the 1960s, and since then has lead the way into what I call the “Third Green Revolution”: urban agriculture. Over the last ten years, the acceptance of city farming in all its manifestations by the urban consumer public has been encouraged and catalyzed by numerous breakdowns in the global food system; the most important and high profile ones being food-born disease outbreaks and crop failures, the latter mostly caused by adverse weather and geological events (e.g., floods, droughts, earthquakes, tsunamis).

The long-term significance of establishing urban agriculture an integral part of the built environment lies in its potential for enabling cities to become self-reliant. In that context, I now have the somewhat perverse pleasure of offering up a second, more positive definition for “circular reasoning.” It’s based on ecological principles established over the last fifty years of intensive research, during which time the details of ecosystem functions and services were elucidated. Not surprisingly, it has been established beyond any doubt that every element (i.e., some 27 at last count) involved in the life cycle of virtually every living entity, be it a bacterium or an elephant, upon the death of that organism, is recycled. The surprise came when it was determined that these essential cycles were almost exclusively facilitated by a myriad of life forms, mostly members of the microbial community. Formerly known simply as geochemical cycles, they have been correctly renamed biogeochemical cycles.

The ecological sciences were given another boost in data collection the moment NASA became involved; in this case focusing on the Earth’s terrestrial flora. Today, there are eight operational LandSat satellites orbiting some 300 miles above the planet using sophisticated monitoring instrumentation, all designed to determine the kind and amount of the types of vegetation present year round (e.g., trees, grasslands, tundra), including all major crops (e.g., wheat, corn, rice, barley, millet). These data have allowed for accurate predictions regarding crop yields, and revolutionized the global commercial commodities markets. Most importantly, the LandSats document the rate of deforestation that is occurring in real time. Complex biological assemblages of plants and animals are being sacrificed at an ever-increasing rate in favor of mono-crops. Deforestation diminishes the ability of terrestrial systems to sequester carbon (CO2) from the atmosphere. Through our creation of more traditional farming, we have taken a circular biogeochemical process of carbon use/reuse and turned it into a straight line. The result is rapid climate change.

Over fifty percent of us now live in cities, with more on the way, so in another 20-40 years, as many as eighty percent may live there. It takes nearly half of the landmass of South America just to provide food for urban dwellers. If things do not change significantly over the next few decades, our lives will become more challenged just to meet our minimal daily requirements for drinking water (2.3 liters) and food (1,200 calories). Radical changes are required now if we are to thrive into the next millennium. Turning straight lines into circles (ecological circles of reuse) is what is needed most. We must restore natural systems to allow them once again to function as our life support system. We must also learn to live sustainably in urban settings (i.e., reduce our encroachment into natural systems in our efforts to obtain more and more essential resources), as we evolve into mega-city dwellers. To accomplish this, municipalities must adopt an ecological approach to city management. Water, food, and energy are the essentials of every functional ecosystem, and the biogeochemical cycles are the mechanisms by which they remain sustainable. Cities must also deal with these in ways reflective of a balanced ecosystem. But in our case, we must employ cutting edge technological solutions to get us there. That is where urban agriculture, especially vertical farming, may offer practical (i.e., affordable) solutions to the problem of supplying enough food for non-rural populations. Urban agriculture also could set the standard for establishing truly sustainable approaches to recycling essential resources such as drinking water and energy production via non-edible crops used to make biodiesel and bio-gas.

In summary, the sustainable city of the future will reflect natural process, characterized by a series of interconnected, interdependent municipal functions designed to maximally conserve essential resources. The planers and managers of those cities will practice circular reasoning to accomplish this highly desirable outcome.

Dickson D. Despommier is an emeritus professor of microbiology and public health at Columbia University and an advocate for vertical farming.