tractor at night working the fields

Urban Growth May Not Happen As Imagined

If the trend of the last 100 years continues, by 2050, three, out of four people will live in urban areas. This urban growth might not be a good thing.

Urban growth is trending to put 4 out of 5 people in urban areas. This steady urbanisation comes from the need to accommodate and support the population rise that took off in the 20th century and added 4 billion people in a hundred years.

In 2020 when we all tried to curb the spread of COVID-19, 56% of us were locked down in cities and urban areas. In Europe, the proportion was 75%, and in Northern America, it was 84%.

Here are the UN records for this trend in urban growth and their projection for 2050.

The explanation is that cities are where opportunities happen, whereas rural areas offer hard work for little financial reward. Cities provide the chance of riches and a more comfortable lifestyle from the trade of physical labour for wages, even if riches are nearly always elusive. Unless you can become a landowner, rural life is trading time for money at modest rates.

The thermodynamic reality is that rural areas, especially in countries with mature economies, receive an energy subsidy from fossil fuel inputs in return for producing excess food to feed the urban populations. This is the necessary energy conversion and transfer that allows people to live in large groups.

In their tractors and machinery, farmers have the power equivalent of a slave army that helps them till fields, plant, nurture, harvest and store food crops and rear livestock to transport to cities. 

A single barrel of oil (42 US gallons or 159 litres) refined and burnt in machines can deliver power equivalent to about 1,700 kW h of work, while a healthy human labourer can perform about 0.6 kW h in one workday.  

Suppose the farmer uses a barrel of oil across his farm machinery daily and in the inputs of fertiliser and pesticides. In that case, it is as though he has commandeered 1,500 workers, even if we assume that oil is less efficient at work than pairs of hands. 

If the UN projection for 4 out of 5 people living in large groups with limited capacity to grow their food is correct, what does it say about this virtual rural labour force?

Urban growth in population size

Before finding an answer, we need to capture another assumption and figure out what the global population will be in 2050

Again the UN tells us this figure will be 9.7 billion.

Part of this increase is baked in because of the population growth in Africa and Asia that has already generated large numbers of youngsters ready to reproduce themselves. All that needs to happen is for these people to remain fed sufficiently to survive and reproduce. The likelihood of this is high given that enough food is grown globally and there are enough fossil fuel inputs available for this to continue for a decade or two longer. Food shortages are more about distribution and access than production.

A catastrophe, even a collapse is possible, but current global food systems could result in 9.7 billion people.

Given the urban growth trend, by 2050 there will be 6.8 billion people in towns and cities fed largely by the efforts of 2.9 billion living in rural areas. This rural population will be 500 million fewer than the current rural population.

This rural community will be able to grow 24% more food than today with the virtual army of labourers provided by the power of fossil fuels. 

The assumption in the population projection and the graph of where these people will live is that the energy subsidy to food production will continue and grow by a quarter in a generation—roughly 1% per annum.

people line up outside a colourful street food vendor in a Chinese city

Photo by Hanny Naibaho on Unsplash

What if the energy subsidy fails?

The extra energy used to grow food is not a subsidy by the government, although many governments do support farmers. It is an energy subsidy that is a consequence of intensive agriculture. 

Machines and inputs (nutrients, pesticides and water) from outside the farm are energy sources for the crop or the livestock. The energy used to power the machines and energy embodied in the extraction and manufacture of all the tools and inputs a farmer uses.

It is hard to put a number on exactly how much external energy it takes to put food onto the plate of a person living in New York or Mumbai, but here are some recent approximations from the US.

graphic showing the energy inputs to food production compared with energy outputs

Source: Bradford, J., 2019. The Future is Rural: Food System Adaptations to the Great Simplification.

In this analysis, roughly eight units of energy are needed to get one unit of energy into an urban human. If food waste is shifted to the supply side, the ratio rises to 14 to 1.

Even if agricultural production is efficient, the food supply system isn’t

And this is just for energy; we could run similar numbers for resources and nutrients. 

At these ratios, the energy subsidy cannot fail. If it does, millions will starve, most of them in cities and towns aggregated from the consequences of urban growth. The historical famines that predominantly affected rural areas due to drought and widespread crop failures will march into the cities.

Future of the energy subsidy.

The reality is that the current forms of energy the farmer uses will not persist beyond 2050. Fossil fuels will either be phased out to reduce greenhouse gas emissions or become too expensive to extract and use. 

This will not be sudden for a couple of reasons. First, the machinery on farms is predominantly powered by internal combustion engines. Replacing these machines with electrical-powered options will take more work and resources than are currently available. Nor will replacing or retrofitting all the road transport vehicles. The ships that take the food worldwide will be especially tough to convert, probably to gas as an interim fuel or directly to hydrogen—the wind is even a possibility. 

The challenge is that alternatives still need to be at scale. And some can never be because limited mineral resources are available to manufacture them.

Then there are the industrial processes that produce nitrogen fertilisers. They use gas as a raw material and a lot of energy. But producers will experience yield gaps and lower production without fertilisers, so this will likely be the last of the subsidies to end.

Energy subsidies will only continue if an alternative energy source comes online. Even then there are limits to the supplies of raw materials to retrofit or replace all the existing farm machinery and infrastructure. 

In short, the future of the energy subsidy to agriculture is perilous.

People will move back to the land and reverse urban growth.

When the subsidy declines, it will mean changes to intensive agriculture.

What will happen is that the alternative food production systems will be more labour-intensive, local, closed, and rely on nature to maintain yields. 

More people will grow food, even those still living in cities.

The solution to not having enough energy inputs on farms is getting people and animals to do the work. Farms will become more circular and self-sustaining, just as they used to be. It will be a back-to-the-future moment with production returning to a net energy surplus.

Alternatively, the whole system collapses, and we enter dystopia.

Suppose that the energy supply didn’t fail but was gradually transitioned into a much lower per capita use. Transition buys time for people to adjust and for the new production systems to appear and replace the energy input-output approach we have today.

What would happen is that people would return to the land. There would be more people growing a proportion of their food.

Here is how we know.

graphic showing the negative correlation between the proportion of population that is rural and the energy consumption per capita

Most countries with at least 50% of the population as rural consume less than 10 barrels of oil per person per year. All the high per capita energy-consuming countries have urban populations.

A handy bonus of slowing urban growth

Returning agricultural production to a net energy source by involving more human labour in food production has bonuses.

Soil health would be more easily gained and less energy-intensive if human cultures were more spread across the landscape. People would more easily eat, dispose of their waste, and maintain their animals inside the plant communities on which the entire system is based. 

Instead, we have disconnected ourselves from productive landscapes, paid to clean up the pollution in cities and feedlots—cities are functionally equivalent to feedlots for people—and then paid to mine, manufacture, transport, and disperse replacement minerals back to the soil. 

Here is how Jason Bradford from the Post Carbon Insitute explains the luxury of long-distance transport of food to cities and long-distance transport of wastes back to farms.

This is called progress. It would be wise to sort out how to return to land what we take from it and dispense with energy-demanding mining and processing. Returning all human waste to fields is entirely possible and was the method by which Chinese and Japanese farmers persisted for centuries. 

Jason Bradford

What sustainably FED suggests

Economic growth and human population growth on the back of fossil fuel subsidies over tha past 100 years have been spectacular. A miracle. No other organism has appropriated exogenous energy and converted it into more making and aggregated populations through urban growth.

We know that organisms given excess resources can grow in numbers. Bacteria and fungi do this all the time. 

But we also know what happens when the resource is used up, and that is what more making does; it uses resources.

So the growth projection—adding the yellow and brown projections in the graph above—is naive. Any healthy sceptic would warn against such simple predictions even if the historical trend was as predictable as this one. 

The coming bust may force those that remain back onto the land. There may not be another choice.

Meantime we should stop thinking that urban growth is given and figure out ways to make what’s coming a transition and not a collapse.

Hero image from photo by Jason Edwards on Unsplash


Mark is an ecology nerd who was cursed with an entrepreneurial gene and a big picture view making him a rare beast, uncomfortable in the ivory towers and the disconnected silos of the public service. Despite this he has made it through a 40+ year career as a scientist and for some unknown reason still likes to read scientific papers.

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