Urbanization is a dominant civilization pattern defining the modern life experience and presenting challenges for maintaining sustainable balance with a fragile planetary ecosystem. The trend of migration from rural agricultural communities into dense cities is a phenomenon that traces back as far as historical records go, and patterns of agglomeration, economies of scale and labor specialization can be observed in the smallest hunter-gatherer tribes, so urbanization can be thought of as a persistent force of human social organization. A frequently reported claim is that cities compared to rural areas on average score higher in certain measures of well being such as education and access to medical care and basic infrastructure - plumbing, electricity, housing. Current forecasts of urbanization predict 67% of global population to be living in cities by 2050. Central to the challenge of urbanization for climate change is food and energy. Is it possible to make the benefical infrastructure and social organization of cities universally accessible to everyone on the planet? Why are there still populations living outside the urban zones? What is the primary employment for rural residents that disincentivices migration? Is full urbanization 90-100%a realistic possibility? Applying an emperical scaling law for cities derived from Kleiber's law predicts the land area required for the 2050 population of 9 billion if condensed into 100 cities would be less than 1% of non-desert global land area. Recently urban designers are exploring the idea of food and energy self-sufficient cities and a frequent response hear during such discussions to defend agriculture outside the city:
Its not economical to produce food in cities because there is not enough land
While they may not mention his name, the idea was formally introduced in 1826 by Johann Heinrich von Thunen in a book The isolated state. In this book he developed a theory of rent and applied to agriculture to predict the land distribution pattern of agriculture in concentric circles around the city based on their yield and transportation costs.
The theory is consistient mathematically and limited to several assumptions
The city is surrounded by wilderness
The city is isolated
Climate and soil quality are consistent
No natural geographic barriers of mountains or rivers
Farmers bear the cost of transportation
Farmers decisions are based on maximizing profits
These assumptions and the mathematical conclusions appear at first to be a fairly straightforward well presented argument supported by empirical observation of concentric rural "hinterland" surrounding a dense urban core that characterize dominant urbanization development trend from early settlements until now in 2019. The assumptions of Farmer's bearing the cost of transportation is true in the sense that the distributors pass this cost on to the farmer by offering a lower price to the farmer than the final sale value. The scale of the transportation in this context is effectively at a global scale, so mountains and rivers are of less significance. Although there are many cities sharing a common hinterland region, the pattern of space-filling outside of dense central cores can easily be extended to a poly-centric pattern and still arrive at a similar geographic pattern and divergence of hinterland and cities. This is probably where the assumption validity stops however, and on more carful inspection, there are a number of exceptions which question the validity and relevance of the argument in modern context.
There is no wilderness
Climate and soil quality are not constant, they are on the decline
Yield - Greenhouses can achieve much higher yields than open field conventional methods
If you interpret the Thunen model literally you end up with everyone living in one massive Burj Dubai tower of babel
Real cities and plant typology is 3D, not 2D
Sunk costs, self-sufficiency premium and homeostasis
Farmers are people that make decisions for multiple factors not only financial profit
Farmers are not the only people that influence land development decisions
There is no wilderness
A popular phrase "planetary urbanism" presents a number of claims, with a central theme that urbanization has now effectively spread and encroached on every last edge of the planet. While there are still some large tracts of relatively isolated ecosystems, they are becoming the minority and the dominant geographic pattern is that these areas are becoming surrounded by developed regions and not the other way around, so now the geography is inverted and more accurately described as a vast region of developed land with isolated pockets of natural reserves. The pace of deforestation does not appear to be stopping so the continuation of a true wilderness, and biocapacity reserve is at risk. The value of a buffer capacity of wilderness is difficult to quantify, but easy to understand that it would be a bad idea to have zero wilderness, which is the current business as usual path.
For any closed system of living organisms the population growth curve over time appears as a sigmoid with two distinct growth periods - exponential, followed by asymptote or decline. Three general scenarios are possible for the global population as it nears the carrying capacity limit :
Growth slows to net zero as the population asymptotically approaches the carrying capacity limit
Decline or complete extinction as a consequence of overshooting the carrying capacity limit with lag effects
New growth period as a consequence of phase-change transition “technology” change in the carrying capacity and/or the main parameters of the survival model.
The reality of the climate change threat is that of the three scenarios, #2 is a real possibility due to the nonlinear characteristics of positive feedback loops “runaway reaction” and singular events that could irreversibly destroy entire agricultural regions crop productivity in a short period of time. The mechanism of population adjusting to carrying capacity on a geological time scale with small incremental changes to birth rates is not particularly noteworthy or cause for alarm. This is not however a realistic description of population adjusting to capacity limits in the current global warming context. Scenarios such as reductions in carrying capacity of 10-30% in a short period of 10-50 years are a real threat. In such scenarios death prior to reproductive age in combination with declining birth rates are both part of the rapid decline in population and restoration to carrying capacity limit. The argument for reforestation or rewilding is both to prevent the worst case of climate change, and also to reserve some ecological carrying capacity buffer for the degree of warming that is already built-in from previous emissions.The argument for a carrying capacity buffer has shown up in several historical cases of colony and settlement management policies - for example the early Puritan governor of the Plymouth Colony in early US colonial history restricted land conversion based on the rational self-interested case of sustainability of the fur trade and political symbiotic relationship dynamics with the Naitive American's.
Climate and soil quality are not constant, they are on the decline
The uncertainty of climate has been a challenge for farmers even in 1826, but this was relatively predictable over long seasons of 5-10 years using hueristics and farmers almanacs. This is fundamentally different. Farmers would need a more than a farmers almanac book to remain profitable in the face of the magnitude and scale of disruptive climate change with global average temperatures rising by 2 or 4C from pre-industrial levels. The recent IPCC report calls to question whether anything will grow in some regions following a singular event like prolonged drought. For "soil" - the model of intensive industrial fertilizer based agriculture changes the traditional ideas about soil. While dirt may be free the marginal cost of fertilizers were not considered in the original Thunen model. Based on principle of conservation of mass - the NPK nutrients stripped from the fields don't just dissapear - they are deposited in the immediate vicinity of the city as food and human waste. In a scenario of rising cost of energy either by natural market dynamics of limited resource or imposed by policy in the form of carbon tax - fertilizer marginal cost may be a profitability deal-breaker and with growing support for cities to achieve zero waste - urban waste may become the new "black gold" for farmers.
Yield - Greenhouses can achieve much higher yields than open field conventional methods
The requirement of access to high skilled labor, lab analysis and capital intensivity of high tech greenhouse present operational challenges for operating greenhouses farm from the shared resources of an urban center. Peri-urban while not completely in contradiction with the basic Thunen argument may be much more attractive than the current rural farming locations. Another factor that influences yield is meat diet. When Thunen developed the model diets were still majority plant based, the trend of excessive meat consumption is a modern phenomenon only in the late 20th century. While nothing is certain, current demographic consumer trends suggest that this pattern may reverse again back to a more plant based diet, which would mean a much smaller footprint area demand and higher overall agricultural yields making urban food self-sufficiency a more realistic opportunity.
If you interpret the Thunen model literally you end up with everyone living in one massive Burj Dubai tower of babel
This visual image while an amusing is not a realistic description of urban typology. Real cities are heterogeneous and fractal leaving lots of gaps, parks and empty unused spaces that for a variety of reasons are not available for rent. These "marginal" spaces not including the roads for most cities are the majority of land areas, whereas the rented "built-up" plot spaces is only a small fraction < 15% of total land area even for highly built-up urban areas with population density > 10,000 ppl/km2. These marginal spaces could be filled with financally viable greenhouses and depending on the population density achieve high self-sufficiency ratios for the city of 50%-80% of dietary needs.
Real cities and plant typology is 3D, not 2D
One of the major technology design trends distinguishing 21st century from the 20th century is design directly in 3D is becoming more accessible. Its hard thinking and especially designing outside of 2D but with the help of 3D computer modeling and also manufacturing methods are assting engineers, designers and widening the range of possibilities. The presence of buildings as vertical extensions create 3D opportunities either by using rooftops, spaces between buildings, the building facades. Attachment to a 2D horizontal plane surface is not a requirement for plants or buildings further increasing the yield potential of the city compared to the hinterland.
Sunk costs, self-sufficiency premium and homeostasis
If at some point a stable urban farming economy is established, feedback dynamics - incuding the organic waste recycling, preferential diet selection of locally grown vs imports for food quality and sunk cost economic motives may create a homeostasis pressure that resists attempts to convert to other land uses even if offers for higher rent are proposed. You can't eat currency or electrons, so just as some people put a high premium on ownership of homes, a similar dynamic may also emerge for food. This hypothesis has evidence from historical real urban developments where settler communities were forcibly relocated by local zoning policy intervention and not by free-market choice of the urban farmers.
Farmers are people that make decisions for multiple factors not only financial profit
Some sticky factor to stay in the hinterland based on homeostasis, sunk costs fallacy and resistance to change, other push factors such as declining farm profitability and desire for economic and social mobility for themselves and their families. Still others may develop an intrinsic concern of the impact of agriculture on climate and the prospects for future generations, and may also decide from ethical conviction for 100% urbanization and rewild the hinterland.
Farmers are not the only people that influence land development decisions