www.buildingsandcities.org/insights/commentaries/climate-change-overshoot-cities.html

Why large cities will need to contract or be abandoned altogether

William E. Rees (University of British Columbia) explains why urbanisation has been a significant contributor to ecological overshoot (when human consumption and waste generation exceeds the regenerative capacity of supporting ecosystems) and climate change.¹ Civil society needs to begin designing a truly viable future involving a ‘Plan B’ for orderly local degrowth of large cities.

Cities as fossil-dependent emergent phenomena

Modern cities and mega-cities exist because they can. No one planned for a metro London of 15 million people, a Shanghai of 29 million or for Tokyo’s spectacular 41 million — that’s more than the population of Canada, the world’s second largest country! Mega-cities and other major cities are truly ‘emergent phenomena’ of the modern techno-industrial age and manifestations of humanity’s explosive growth in the past two centuries.  And it truly was explosive—300,000 years of anatomically modern human history had passed before the population reached its first billion in the early 19th Century. Then, in just 200 years, 1/1500^th as much time, humanity ballooned eight-fold to top eight billion in 2023; meanwhile, real gross world product expanded 100 times.  Remarkably, economists, politicians, urban planners and most ordinary citizens consider this brief spurt of exponential economic and population growth—particularly urban population growth—to be the norm. We’ve become addicted to it. But in reality, it is the single most anomalous period in human history.  More remarkably still, many people at all levels expect the urban future to unfold as a technology-enhanced version of the recent past!  The United Nations projects that cities will add more than two billion people—if only mostly to their slums and barrios—by 2050 (U.N. 2018).

It is rarely acknowledged but a crucial fact that this explosive anomaly was made possible by fossil fuels (FF). Coal, oil and natural gas are prodigious sources of potential and possibilities. Abundant cheap energy was, and still is, necessary, not only to ‘build out’ our cities, but also to supply them with everything—all the food, consumer goods, and raw materials needed to defend urban infrastructure against the corrosive workings of the 2^nd law of thermodynamics. (The 2^nd law is manifested in the tendency of everything to wear out and run down—consider the often dismal state of roads, bridges and other infrastructure in many large cities today.) Stand on the sidewalk near a major construction or repair site on a busy road in any modern city—the clamour and din of excavators, cement mixers, tipper-trucks and power tools blending with the road noise generated by passing delivery and passenger vehicles is the sound of raw energy—mostly FF—at work. All our transportation networks, and electronic communications systems, our water supply, sewage disposal and related urban infrastructure are, to a large degree, FF dependent.  And what about the prodigious quantities of nutrients and calories needed to sustain the world’s urban billions?  Fossil fuels and petroleum-derived inputs (e.g. pesticides, fertilizers) inject ten times as much energy into agriculture and food processing as does photosynthesis and are thus crucial to the industrial-scale food production that provisions every major city. 

Bottom line? Modern cities—mega-cities in particular—are the most spectacular physical products of, and remain largely dependent on, fossil fuels. Other factors, particularly, improving sanitation and public health standards (themselves often FF dependent) contributed to humanity’s exuberant expansion, but it is fossil energy that made the modern mostly urban world possible.

And that presents a problem.

Climate change and the energy conundrum

Cities’ profound dependence on FFs weighs heavily on the future of urbanisation. First, FFs are a major source of CO2 emissions—CO2 is an unavoidable entropic product of fossil fuel combustion and the principal driver of anthropogenic climate change. With increasing FF use, atmospheric CO2 and other GHG concentrations are increasing. The current trajectory implies a catastrophic three to four Celsius degrees mean global warming in this century, far above the existing one C^o+ warming that is already causing unprecedented climate havoc around the world. In recognition of unfolding climate disaster, parties to the United Nations Framework Convention on Climate Change (UNFCC) committed in the 2015 COP21 Paris Agreement to hold the increase in global average temperature to well below 2°C above pre-industrial levels and pursue efforts to limit the temperature increase to 1.5°C above pre-industrial levels” (IPCC 2018).

Commitment is one thing, decisive action another; the official response has been dismal. The voluntary emissions reductions — nationally determined contributions that were pledged in Paris — constitute only a third of the reductions needed to limit warming to even 2°C and are not always being honoured. As a result, emissions continue to rise, global mean temperature is at a record high and many climate scientists believe the world has already blown past the more stringent 1.5°C warming limit (Hansen et al.2023). (When the final records are compiled, 2024 is expected to be the first year to exceed the 1.5°C warming limit set by the UN Paris Agreement.)

But what about the much-vaunted green clean energy revolution?  It is true that rapid growth of so-called modern renewable energy (RE), mostly by wind turbines and solar PV panels, has made significant inroads displacing FF (mainly coal) from electricity production in a few countries. However, green electricity merely adds to existing energy sources. Fossil energy use has been expanding even faster and actually reached record levels in 2024. More than half the FFs ever consumed by humanity have been burned since 1992, the year the UN committed to limiting emissions!  As a result, CO2 emissions have grown from 22.5 billion tonnes (Gt) in 1992 to 41.6 Gt in 2024 and atmospheric CO2 levels grew from 360 to 422.5 parts per million to 52% above pre-industrial levels. 

Bottom line?  FFs still provide ~81% of the urban world’s primary energy demand, a proportion that is essentially unchanged since the UNFCC was framed in 1992.  Any positive effect on emissions of the massive investment in so-called clean green has largely been neutered by increasing global demand for energy.  Wind and solar power (W&S), where most investment is going, gave usonly 14.3% of global electricity production in 2023 (compared to ~60% by fossil fuels).  But electricity constitutes only ~19% of global energy supply. Thus, despite the promotional hype, billions invested, and rapid capacity growth, W&S electricity contributed only ~2.7% to the world’s final (consumer level) energy consumption in 2023 (data from E.I. 2024).  

The fact is there is no energy transition! (Fressoz 2024).

But don’t think for a moment the situation couldn’t be worse.

Overshoot: the over-riding existential threat

Global heating poses a horrific challenge, but climate change is only one co-symptom of a much greater malaise. Explosive growth has propelled the human enterprise into a state of advanced ecological overshoot (EO) (Catton 1982, Rees 2023). EO exists when the human consumption of bioresources exceeds the regenerative capacity of our supporting ecosystems, and the production of wastes overwhelms their assimilative capacities. Co-symptoms include plunging biodiversity, ocean acidification, tropical deforestation, land/soil degradation, the pollution of land air and water, contamination of food supplies, etc., etc.—all so-called ‘environmental’ problems.  When in overshoot, the world community can achieve further growth—and even just maintain itself—only by depleting essential natural capital and overtaxing the life-support functions of the ecosphere including the climate system, i.e. by destroying the biophysical basis of its own existence.

And that is precisely what we are doing. The global footprint network monitors the annual occurrence of ‘Earth Overshoot Day,’ the date in the year when humanity’s demand for ecological resources exceeds nature’s budget (supply) for that year (GFN 2024). Each year, Overshoot Day occurs a little earlier as demand increases and eco-production declines with accelerating ecosystems degradation—in 2024, it fell on August 1. Remember, the difference between human demand and nature’s supply of even renewable resources can be made up only by depleting remaining natural capital stocks—fish stocks, forests, soil organic matter and nutrients, ground water, etc.—that took thousands of years to accumulate in nature, and by over-filling nature’s waste sinks.  (Even climate change is a waste-management issue—CO2 is the greatest waste by weight of industrial economies.)

Think about this for a moment.  Overshoot means that humanity is running an ecological deficit, a material deficit far more important than the fiscal deficits that preoccupy politicians.  Numerous recent analyses present the evidence that that urban civilisation is on track to experience a ‘ghastly’ future (e.g. Bradshaw et al. 2021; Fletcher et al 2024). Yet most politicians, like their constituents, have never heard of overshoot. Instead, popular interest swings with media attention among its various individual symptoms—climate change, micro-plastic pollution, falling sperm counts, the SARS-CoV-2 pandemic—without connecting the dots.  The fact is that humans generally have great difficulty thinking in complex systems terms. This cognitive impairment is crucial because overshoot is the ultimate ecological meta-problem. Biodiversity loss, air/land/water pollution, climate change, impending resource scarcity—pick your issue—all result from overshoot.  We cannot ‘solve’ any major symptom of overshoot, including climate change, in isolation from any other. Conversely, tackling overshoot directly would address all its symptoms simultaneously.

But here’s the rub—in simple terms, overshoot means there are too many people consuming and polluting too much (Rees 2023).  By definition, the only way to ‘tackle’ EO is by significant absolute reductions in energy/material consumption and smaller human numbers—and this solution is anathema to modern techno-industrial (MTI) culture.

Which brings us back to population, urbanisation and the future of cities.

Between a quintessential ‘rock and a hard place’

Any political leader who moved aggressively to cut FF use by nearly 50% as required by 2030 (W.E.F. 2022) without viable substitutes and a comprehensive socioeconomic restructuring plan would be courting economic and political disaster. Most countries would face strict rationing of energy and the world would suffer from: continued global warming in the short term (even with further expansion of ‘clean’ electricity); increasingly erratic weather; inadequate energy supplies; economic contraction; falling incomes; rising inequality and widespread unemployment; broken supply lines, particularly interurban transportation; failing agriculture; food and other resource shortages; local famines and global food shortages; civil unrest; mass migrations and abandoned cities; geopolitical chaos.  Looking ahead, the expected 60% expansion of cities (by 2050) could not occur; indeed, it would likely be impossible to maintain existing large cities and mega-cities. Whither their existing populations?

All of which explains why global society has taken an alternative course. Most senior governments, urban administrations, international organisations, many academic analysts and even environmental organisations have bought into the mythic green renewable energy (RE) transition.  Governments have even actively helped delude their populations into thinking we can ‘carry on carrying on’ equipped with heat pumps, EVs, and ‘smarter’ cities. 

It's an easy sell—why would people fear an existential crisis if no major life-style changes are necessary to resolve it—or, indeed, if new technologies present opportunities for economic prosperity? Note that the only politically feasible ‘solutions’ to climate change—high-tech wind turbines, solar photovoltaics, hydrogen fuels, electric vehicles, heat pumps, as yet unproved carbon-capture and storage technologies, etc., all require major capital investment. These techno-fixes serve as stimulants for economic growth, provide well-paying jobs and generate opportunities for profit. A prosperous future is assured. What’s not to like?   

Plenty as it turns out. Far from addressing our eco-predicament, these technologies are all FF dependent and merely extend the eco-catastrophic status quo.  As Spash (2016) and others have observed, politically acceptable ‘climate actions’ are those that make capitalist growth economies appear to be the solution to, rather than the cause of, our ecological crisis. The mainstream is essentially promoting business-as-usual-by-alternative-means. This approach is not ‘solving’ climate change and is actually worsening its cause, overshoot.  Moreover, because the energy transition has barely started, we are not even getting the ‘by-alternative-means’ part.  The reality is that the world has opted for continued fossil fuel dependence as long as economically accessible supplies hold out.  

Just what is going on here? Mainstream governments, major corporations and their allies are behaving as exemplary temporal and spatial discounters: they prefer to accept the uncertain risk of future catastrophic climate change which (they hope) will mainly affect other people somewhere else, than the immediate certain risk of economic and social chaos at home.² Moreover, as devotees of MTI sensibilities, they are bound to seek solutions self-referentially from within the neoliberal techno-expansionist paradigm. Assertive policies that would actually work to reduce carbon emissions but create energy supply shortages or other threats to economic growth are inadmissible; significant lifestyle changes are not on the table; population or family planning is still taboo.  We continue to ignore/deny the reality of overshoot.   

So, what’s at stake?  On the world’s chosen growth-bound tack, fossil fuel use will continue for years and decades to come. Even in the best case, we can expect a catastrophic 2.4°C warming which means increasingly erratic weather; more and longer heat waves/droughts; more energetically violent storms and floods; extended wildfire seasons; accelerating desertification; melting permafrost and methane releases; water shortages; failing agriculture; widespread famine; the flooding and loss of many coastal cities; breakdown of national highway and marine transportation networks; the abandonment of increasingly uninhabitable regions; mass migrations; collapsed economies and geopolitical chaos.  According to Environmental Risk Outlook 2021, at least 414 cities with a total 1.4 billion plus inhabitants, are at high or extreme risk from a combination of pollution, dwindling water supplies, extreme heat stress, and other impacts of climate change. In the more vulnerable parts of the world, severe heat and drought will render even rural regions uninhabitable. Recent research shows that just 2.7°C of warming alone could push as many as three billion people outside humanity’s historic safe climate niche in this century (Lenton et al. 2023). Again, there could be mass migrations involving one to two billion eco-refugees by mid to late century (see Baker 2021). 

The world is in a genuine predicament, trapped between the toughest of rocks and most unyielding of hard places—decisive action would destroy the world as we know it; inaction could destroy the world as we know it.  Predicaments have no solution, only outcomes.  From this perspective, contrary to mainstream projections, the sun may well be setting on the era of urbanisation—how can anyone think seriously that, in present circumstances, we can build out cities to accommodate sustainably an additional two billion people?  (Using what source of energy?)  Devoid of cheap energy, cut off from vital supplies, economically drained, and hammered by extreme weather events, even existing large cities and megacities can only contract or be abandoned. Many will not survive the end of the century. Domestic chaos and widespread geopolitical conflict seems inevitable. 

In Triumph of the City, his paean to human achievement, urban economist Edward Glaeser (2011) posits that “If the future is to be greener, then it must be more urban. For the sake of humanity and our planet, cities are—and must be—the wave of the future” (p. 222). Ironically, the ecological catastrophe that Glaeser supposed cities could head off may, instead, stop urbanisation in its tracks.

Epilogue: becoming citizens of Earth

"Localisation stands, at best, at the limits of practical possibility, but it has the decisive argument in its favour that there will be no alternative."
(Fleming 2021).

Modern techno-industrial (MTI) sensibilities have created a brute-force civilisation, one based mostly on violent, unsophisticated, technologies­—digging up, chopping down, ploughing under, fishing out, pumping dry, burning up, etc.—all the time oblivious to the complex dynamics of the ecosphere or to the impact on others species or less ‘advanced’ peoples. In the process, modern H. sapiens has become the world’s greatest geological force, eroding more of Earth’s surface, depositing ten times as much sediment and moving more other materials around to build our cities and infrastructure than all natural forces combined (Wilkinson 2005; BGS 2018). We have built MTI civilisation with the flesh and bones of planet Earth.

Two additional defining qualities of MTI society are globalisation and urbansation but these processes too compromise the functional integrity of the ecosphere and, with it, long-term human security.  Both will necessarily shrivel or terminate with the coming great contraction.  

None of this means that ordinary people can do nothing to ease humanity into the unfamiliar future.  Clearly, the time has come for people to acknowledge biophysical realities and adapt accordingly.   H. sapiens is a biological entity but must evolve culturally from our status as primitive-parasite-that-consumes-its-host, to contributing-commensal-partner within the ecosystems that sustain us. 

As globalisation erodes and related supply chains fray to breaking, it will be necessary to insulate ourselves, loved ones and friends against the worst effects of the transition, whatever final form it takes. Perhaps the wisest strategy for individuals and communities is to begin designing and implementing programs for eco-education, community-building, and active political engagement in defining a truly viable future. The initial goals should be to raise to popular consciousness the novel eco-social context that is already unfolding and to organise discussion of key elements for inclusion in a ‘Plan B’ for orderly local degrowth. An initial focus should be on the ‘HOW’ question. How—by what (preferably non-violent) means—do we convince both our local political leaders and fellow citizens to join in taking the necessary steps to adapt to evolving circumstances? 

Major elements of ‘Plan B’ will be development of:

• land-use plans for smaller-scale more self-reliant human settlements tuned to local circumstances and
• strategies to re-localise essential economic activities particularly food production/processing, cloth and clothes-making, and essential small-scale manufacturing (Rees 2022).

It is a mistake to think of such necessary adjustments as regressive.  On the contrary, there is no greater scientific challenge for MTI peoples that to learn to live in tune with the continuous processes and harmonic rhythms of nature.  Farmers, for example, must become skilled applied ecologists—permaculture and agroecology require a much more sophisticated and nuanced understanding of the relationships among soils, weather and climate than does high-input industrial agriculture. Advanced agroecological practices conserve and enhance the soil and microbial communities creating it which is why they are more productive on the smaller plots of land that will frame future farming.  Similar conceptual ‘inversions’ of present destructive practices remain to be discovered and applied in every domain of human economic activity.

The bottom line?  Becoming responsible citizens of Earth is a challenge like none other in human evolutionary or civilisational history.  But it also presents unique creative opportunities for all those willing to face the future with eyes open. Above all, we must let the creative juices flow as if the continuity of civilised life depends on it—because it does! 

Notes

1.     For a more fully detailed analysis, see Rees (2022).

2.     Besides, if today’s governments delay, extreme global heating becomes someone else’s problem tomorrow.

References

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