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1. Introduction and Purpose
This paper examines the human population conundrum through the lens of human
evolutionary ecology and the role of available energy. My starting premises are as follows:
(1) Modern techo-industrial (MTI) society is in a state of advanced ecological overshoot
(for an excellent introduction to overshoot see William Caon's classic, Overshoot [1]).
Overshoot means that even at current global average (inadequate) material standards, the
human population is consuming even replenishable and self-producing resources faster
than ecosystems can regenerate and is producing entropic waste in excess of the ecosphere's
assimilative capacity [2,3]. In short, humanity has already exceeded the long-
term human carrying capacity of the earth. The fossil-fuelled eight-fold increase in human
numbers and >100-fold expansion of real gross world product in the past two centuries
are anomalies; they also constitute the most globally-significant ecological phenomena in
250,000 years of human evolutionary history, with major implications for life on Earth. (3)
H. sapiens is an evolving species, a product of natural selection and still subject to the same
natural laws and forces affecting the evolution of all living organisms [4,5]. (4) Efforts to
address the human demographic anomaly and resulting eco-crisis without aempting to
override innate human behaviours that have become maladaptive are woefully incomplete and doomed to fail.
Within this framing, the overall objective of the paper is to make the case that, on its
present trajectory and regardless of the much-lauded demographic and so-called renew-
able energy transitions, the sheer number of humans and scale of economic activity are
undermining the functional integrity of the ecosphere and compromising essential life-
support functions. Unaddressed, these trends may well precipitate both global economic
contraction and a significant human population 'correction'--i.e., civilizational collapse--
later in this century.
2. The Nature and Nurture of Overshoot
Both nature and nurture contribute to the overshoot crisis, but the natural component
is mostly ignored. Indeed, most denizens of MTI society do not think of themselves prod-
ucts of evolution, i.e., of Darwinian natural selection. Many resent even being reminded
that they are animals.
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3. The Population Connection
"The human mind serves evolutionary success, not truth. To think otherwise is
to resurrect the pre-Darwinian error that humans are different from all other
animals" (John Gray, [31]).
Which brings us back to the population conundrum. In the simplest terms, overshoot
results from too many people consuming and polluting too much. The immediate physical
cause is excess economic throughput (i.e., resource consumption and waste production), but
throughput is itself driven by both rising incomes and population growth. Most people tend
to spend/consume to the limit imposed by their discretionary incomes (and, since the introduction
of easy credit, often well beyond). High-income countries and populations are
therefore responsible for three quarters of excess material consumption and pollution to
date [32]. Even in 2021, "the top 10% of emitters were responsible for almost half of global
energy-related CO2 emissions...this section] compared with a mere 0.2% for the bottom 10%" [33]. For
the past several decades, however, incremental increases in humanity's consumption-based
ecological footprint (EF) and carbon emissions have been driven more by population growth
than increased incomes/consumption in all income quartiles. Indeed, population growth accounted
for ∼80% of the increase in the total human EF above what would have accrued
had populations remained constant even as incomes increased [34,35].
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Figure 1. The anomalous fossil-fuelled human population boom.
Click the image to enlarge.
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4. On Energy Gradients: H. sapiens as a 'Dissipative Structure'
"...this section]we use 30 percent of all the energy, in the United States. That isn't bad; that
is good. That means that we are the richest, strongest people in the world and
that we have the highest standard of living in the world. That is why we need
so much energy, and may it always be that way" (US President Richard Nixon,
November 1973 [48]).
The history of human population growth underscores a key factor to understanding
the eco-crisis, one that is generally ignored by economists and demographers--the population
bomb was assembled during the industrial revolution and exploded in the 19th
century with the expanding use of fossilized organic maer that took hundreds of millions
of years to accumulate. The wealth creation and technologies enabled by fossil fuels (FF)--
including fertilizers and pesticides--reduced or eliminated various historically important
forms of negative feedback, freeing the world's human population to grow exponentially
for the very first time. The fossil-powered explosion of the human enterprise triggered the
most significant period of global ecological degradation in 250,000 years of human evolutionary history.
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Figure 2. GDP is proportional to oil consumption (Log scales).
Graph courtesy of Arthur Berman.
Click the image to enlarge.
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5. The World's Response to Overshoot
"Overshoot is overshoot. Once your civilization starts to consume more than
what naturally gets regenerated in its folly to pursue infinite growth on a finite
planet, collapse is only a maer of time" (B [63]).
Humanity's evolutionary trajectory and our recent period of industrial expansion
have obviously generated a truly unique eco-predicament for humanity--humans are innately
expansionist, and MIT culture is growth-addicted, but material growth on a finite
planet must eventually cease. The most encouraging sign of awakening to this contradiction
is that an international planned 'degrowth' movement is gathering momentum, particularly
in Europe [64]. Even members of the European Parliament are openly concerned
about the risks associated with continued economic growth [65]. Such concerns are stimulated
by increasing numbers of science-based analyses and popular reports that, even
without mentioning overshoot, broach the possibility that MTI societies are facing economic
and population collapse [66-68].
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6. Summary and Conclusions: It's Really Quite Simple
"Without a biosphere in a good shape, there is no life on the planet. It's very simple.
That's all you need to know. The economists will tell you we can decouple
growth from material consumption, but that is total nonsense...this section] If you don't manage
decline, then you succumb to it and you are gone" (Vaclav Smil, [102]).
H. sapiens, like all other species, are naturally predisposed to grow, reproduce, and
expand into all suitable accessible habitat. Physical growth is natural, but is only an early
phase in the development of individual organisms; growth in sheer scale, including population
growth, is characteristic of early phases of complex living systems, including human societies.
However, both material and population growth in finite habitats are ultimately limited by the
availability of essential 'inputs', by the capacity of the system's environment to assimilate
(often toxic) outputs, or by various forms of negative feedback as
previously listed. Growth will cease, either by "design or disaster" [103]
For most of H. sapiens' evolutionary history, local population growth has, in fact, been
constrained by negative feedback. However, improved population health (lower death
rates) and the use of fossil fuels. particularly since the early 19th century, enabled a period
of unprecedented food and resource abundance. In nature, any 'K'-strategic species population
enjoying such favourable conditions will expand exponentially. Growth will generally
continue until excess consumption and habitat degradation once again lead to food
shortages and starvation, or disease and predation take their toll. The population then
falls back below the long-term carrying capacity of the habitat and negative feedback eases
off. Some species repeatedly exhibit this cycle of population boom and bust.
Humanity is only a partial exception. The abundance generated by fossil fuels ena-
bled H. sapiens, for the first time, to experience a one-off global population boom-bust
cycle (Figure 1). It is a 'one-off' cycle because it was enabled by vast stocks of both potentially
renewable self-producing resources and finite non-renewable resources, including
fossil fuels, which have been greatly depleted. No repetition is possible. As Clugston argues,
by choosing to industrialize, Homo sapiens unwiingly made a commitment to
impermanence [77]. We adopted a self-terminating way of life, in which the finite resources
that enable our industrial existence would inevitably become insufficient to do so.
The physical mechanisms are simple. Living systems, from individual cells through
whole organisms to populations and ecosystems, exist in nested hierarchies and function
as far-from-equilibrium dissipative structures [104]. Each level in the hierarchy depends
on the next level up both as a source for useful resources (negentropy) and as a sink for
degraded wastes (entropy). As Daly [8, 9] reminds us, the human enterprise is a
wholly-dependent subsystem of the ecosphere; it produces and maintains itself by extracting
negentropic resources from its host system, the ecosphere, and dumping degraded entropic
wastes back into its host. It follows that the increasing structural and functional
complexity of the human sub-system as a far-from equilibrium-dissipative structure (a
node of negentropy) can occur only at the expense of the accelerated disordering (increasing
entropy) of the non-growing ecosphere. Indeed, humanity is in overshoot--global
heating, plunging biodiversity, soil/land degradation, tropical deforestation, ocean acidification,
fossil fuel and mineral depletion, the pollution of everything, etc., are indicative
of the increasing disordering of the biosphere/ecosphere. We are at risk of a chaotic breakdown
of essential life-support functions [105].
Little of this is reflected in contemporary development debates or in discussions of
the population conundrum. The international community's response to incipient biospheric
collapse is doubly disastrous. MTI culture's commitment to material growth, including
continued FF use (Track 1), condemns humanity to the predictably dangerous
impacts of accelerating climate change; at the same time, our pursuit of alternative energy
sources (themselves FF dependent) in order to maintain the growth-based status quo
(Track 2) would, if successful, assure the continued depletion and dissipation of both
self-producing and non-renewable resources essential for the existence of civilization.
The mainstream view of population asserts that the growth rate is declining so "not
to worry"--or worry that population decline is bad for the economy! Even the base assertion
is controversial. Jane O'Sullivan points out that the rate of decline has itself declined
in this century. She argues that UN demographers have thus 'persistently underestimated
recent global population, due to their over-anticipation of fertility declines in high-fertility
countries' [106]. The human population continues to grow at about 80 million per year--
O'Sullivan argues that the number is closer to 90 million--and its ultimate peak is highly
uncertain. Renewed negative feedback may well end growth well before the population
reaches the UN's expected 10.4 billion in the late 2080s.
It is crucial to remember that, right or wrong, conventional projections ignore the fact
that the ecosphere is not actually now 'supporting' even the present eight billion people.
The human enterprise is growing and maintaining itself by liquidating and polluting essential
ecosystems and material assets. In short, even average material living standards
are corrosively excessive, yet, in 2019, 'almost a quarter of the global population...this section] lived
below the US$3.65 per day poverty line, and almost half, 47 percent, lived below the
US$6.85 poverty line' [107] and the world considers sheer material growth as the means
to address this problem. Following this path, eco-destruction will ramp up, increasing the
probability of a self-induced simplification and contraction of the human enterprise.
Baring a nuclear holocaust, it is unlikely that H. sapiens will go extinct. Wealthy,
technologically advanced nations potentially have more resilience and may be insulated, at
least temporarily, from the worst consequences of global simplification [108]. That said,
rebounding negative feedbacks--climate chaos, food and other resource shortages, civil
disorder, resource wars, etc.--may well eliminate prospects for an advanced world-wide
civilization. In the event of a seemingly inevitable global population 'correction', human
numbers will fall to the point where survivors can once again hope to thrive within the
(much reduced) carrying capacity of the Earth. Informed estimates put the long-term
carrying capacity at as few as 100 million [109] to as many as three billion people [110].
It is uncertain whether much or any of industrial high-tech can persist in the absence
of abundant cheap energy and rich resource reserves, most of which will have been extracted,
used, and dissipated. It may well be that the best-case future will, in fact, be powered
by renewable energy, but in the form of human muscle, draft horses, mules, and oxen
supplemented by mechanical water-wheels and wind-mills. In the worst case, the billion
(?) or so survivors will face a return to stone-age life-styles. Should this be humanity's
future, it will not be urban sophisticates that survive but rather the pre-adapted rural poor
and remaining pockets of indigenous peoples.
Bottom line: Any reasonable interpretation of previous histories, current trends, and
complex systems dynamics would hold that global MTI culture is beginning to unravel
and that the one-off human population boom is destined to bust. H. sapiens' innate expansionist
tendencies have become maladaptive. However, far from acknowledging and overriding
our disadvantageous natural predispositions, contemporary cultural norms reinforce
them. Arguably, in these circumstances, wide-spread societal collapse cannot be
averted--collapse is not a problem to be solved, but rather the final stage of a cycle to be
endured. Global civilizational collapse will almost certainly be accompanied by a major
human population 'correction'. In the best of all possible worlds, the whole transition
might actually be managed in ways that prevent unnecessary suffering of millions (billions?)
of people, but this is not happening--and cannot happen--in a world blind to its own predicament.
References
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ABOUT THE AUTHOR
William E. Rees is a population ecologist and ecological economist. He is Professor Emeritus and former Director of the University of British Columbia's School of Community and Regional Planning; a founding member and former President of the Canadian Society for Ecological Economics; a founding Director of the One Earth Initiative; and a Fellow of the Post-Carbon Institute. Professor Rees' research focuses on the biophysical requirements for sustainability and the policy implications of global ecological trends. He is perhaps best known as the originator, and co-developer with his graduate students, of Ecological Footprint Analysis (EFA). EFA shows that the human enterprise is already in ecological 'overshoot' and that we would need 4.4 Earth-like planets to support just the present world population at Canadian material standards. Such findings led to a special focus on cities as particularly vulnerable components of the human ecosystem and on psycho-cognitive barriers to ecologically rational behaviour and policy. Professor Rees has authored hundreds of peer-reviewed and popular articles on these and related topics.
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