We know how many people the earth can support
First online: 25 November 2020
Christopher
Tucker
Chairman, American Geographical Society
tucker@americangeo.org
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DOI: 10.3197/jps.2020.5.1.77
Licensing: This article is Open Access (CC BY 4.0).
How to Cite:
Tucker, C. 2016. 'We know how many people the earth can support'. The Journal of Population and Sustainability 5(1): 77–85.
https://doi.org/10.3197/jps.2020.5.1.77
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A quarter century after Joel
Cohen asked the essential question “How Many People can the Earth Support?”,
this article offers an answer, based on new science and geographical analysis,
and asserts that we have long ago exceeded our planet’s long term ecological
carrying capacity that optimistically can only support 3 billion modern
industrialized humans. While agreeing that strategies based on reducing
consumption are sorely needed to live within our planet’s carrying capacity,
the impending explosion of the global middle class promises to render
consumption-only strategies inadequate, in the face of runaway population
growth and the accumulation of massive ecological debt. Noting recent
studies that project global population to begin to decrease in 2064 after
peaking at 9.7B, it is asked why we don’t act now to accelerate this already
inevitable trend with enhanced investment in women’s empowerment, education,
and access to family planning technologies. This paper calls for a goal
of achieving 1.5 total fertility rate (TFR) by 2030 to bend the global
population curve, begin relieving the ecological burden humanity has foisted on
our planet, and to decrease human population as we approach 2100 to something
closer to the long term ecological carrying capacity of our planet.
Keywords:
carrying capacity; ecological debt; runaway population growth; women’s
empowerment.
There is absolutely no doubt
that runaway population growth, and our ever growing human footprint have led
us to overshoot our planet’s long term ecological carrying capacity. Our
industrialization of the Earth’s surface has systematically deleted ecosystem
goods and services that our species, and all other species, rely on. As
we add 80 million humans to the planet each year – the equivalent of ten New
York Cities – each additional human places even more demand on our planet for
resources. All the while, we steadily increase the volume and geographic
spread of humanity’s persistent and accumulating wastes, further burdening our
ever diminishing, and already beleaguered ecological resources. Not only
have we exceeded our planet’s carrying capacity, but we have managed to incur
an ecological debt that will take generations to pay down, if ecological
catastrophe does not exact its toll on us first.
Yet,
we still tend to do little but admire the global population curve as it
progresses ever upwards, occasionally bantering about when it might level off,
as though fertility is completely out of our collective power to affect.
Before we annihilate the planet from which we evolved, and which fundamentally
sustains our species, perhaps we need to change how we approach the subject of
population.
The way the world once was
All of
our assumptions about population today are so utterly modern. It is
sometimes hard to envision how the world once was. For millennia before
the industrial revolution, infant mortality was so high that despite high
fertility rates, global population grew at a mere 0.04% between 10,000 BCE and
1750 AD, hovering barely above replacement level (Volk and Atkinson,
2013). Roughly, this led to a doubling of the world population, or less,
every thousand years or so – until the most recent millennium. Before the
dawn of our ever-improving agricultural and technical skills, humanity was just
able to eke out an existence, holding well below 10 million individuals for
hundreds of thousands of years. The combined power of the agricultural,
industrial, and scientific revolutions transformed human existence, and led to
a steady decrease in infant mortality (and maternal mortality), while decreases
in fertility lagged considerably, resulting in a population explosion that we
have admired as a centerpiece of modernity – part of
what we rightly call ‘progress’. This progress broke the stability
feedback loop, allowing runaway population growth which has decimated the
ecosystems that support our species, and undermined our planet’s carrying
capacity. Of course, we have recognized that in recent decades, the most
developed nations have seen their fertility taper off without conscious policy
making on the matter, in places where women have been empowered, educated,
integrated into the workforce, and achieved access to family planning
technologies. This, of course, raises the question why small, educated,
and prosperous families are not held up as the hallmark of modernity and
progress, instead of runaway population growth.
How many people can the earth
support?
Joel
Cohen’s 1995 question is the most important question that every citizen and
leader should be asking themselves and each other, every single day (Cohen,
1995). Yet, a quarter century has gone by, and we have collectively
failed to take it seriously. For a variety of reasons that have been
exhaustively covered elsewhere, population growth has not been a mainstream
topic of discussion since the 1970s. The doubling of the world population
since 1900 was openly discussed as we approached the first Earth Day in 1970
(e.g., 1.6 billion to nearly 3.7 billion). Since this first Earth Day, a
half century ago, we have become transfixed by an endless stream of ecological
catastrophes and human tragedies, somehow remaining silent on what has become
yet another doubling of the world population from nearly 3.7 billion to more
than 7.7 billion. We have refused to publicly discuss how these
catastrophes and tragedies are in many ways simply symptoms of the runaway
population growth that has undermined our planet’s long term ecological
carrying capacity.
How
many people can the Earth support? In my book A Planet of 3 Billion (www.Planet3Billion.com), I offer my
analysis, including a review and critique of a variety of approaches to
calculating the Earth’s carrying capacity (Tucker, 2019a). In that book,
I invite everyone to differ with my analysis – if only you will show your data
and your math. For the sake of this article, I will forgo a defense of my calculation, which I consider a very
optimistic assessment. It is easy not to take issue with less optimistic
assessments that come in lower than 3 billion. Higher assessments tend to
demonstrate gaping blind spots regarding certain dimensions of humanity’s vast
and variegated ecological footprint.
In
rough terms (give or take a billion) we actually have a very good sense of how
many people the Earth can support. We know that we have overshot our
planet’s long term ecological carrying capacity. Even if we achieved a
carbon-neutral (or even carbon-negative) society, the larger human footprint we
would continue to exert on our planet, if population growth continued
unchecked, would still have us exceeding our planet’s carrying capacity.
Scientists’ warning
The
climate change community struggled for decades to gain widespread acceptance of
its scientific findings. While fighting tooth and nail to get people to
accept that human carbon emissions are driving climate change, this community
remained largely silent on the obvious reality that the addition of more humans
increases the volume of these carbon emissions. There was a cultural
predisposition to blame consumption over population growth for our ever growing
carbon footprint – in part to avoid inappropriately blaming poorer nations for
a carbon footprint that has been overwhelmingly driven by rich nations.
This all changed in November 2019, when 11,000+ scientists signed on to the
“Scientists’ Warning on Climate Change” in the journal BioScience
– and for the first time called for the stabilization and then decrease of
human population if we are to avert climate catastrophe – even assuming we were
able to materially reduce consumption in the developed world, and stem growing
consumption in the developing world as billions race to join the global middle
class (Ripple, et.al., 2019). Some climate action advocates will no doubt
take a bit of time to incorporate this scientific consensus into their
orthodoxy and their calls for action. But, the seal has been broken, and
runaway population growth is now a mainstream concern within the climate
science, climate action, and climate restoration communities.
Unfortunately,
the carbon emissions driving climate change are just one small portion of the
larger human footprint. Our human footprint is much larger – perhaps 10
times larger. As I like to say, “What if climate change were twice as bad
as the worst projections, and still only 1/10th of the problem that humanity
has foisted on our planet?” (Tucker, 2019b). This makes the urgency of ending
runaway population growth many times more urgent than that communicated in the
‘Scientists Warning’.
Bending the global population
curve
As we
quickly approach 8 billion, adding 80+ million additional souls (again, the
equivalent of 10 New York Cities) to our planet each year, so many are confused
by basic statistics. Whether it is journalists or their editors, the
rampant confusion over a decline in the rate of population growth versus a
decline in population continues to muddy these issues in the popular
mind. When icons such as Elon Musk and Jack Ma take the world stage and
warn of population collapse, while we are actually facing runaway population
growth, the average citizen cannot be expected to keep things straight (Clifford,
2019).
While
the global Total Fertility Rate (TFR) does indeed continue to decline little by
little,[1] even modest percentages of annual growth
atop the existing enormous global population base means massive increases in
total numbers, and massive increases in the crushing weight of humanity’s
ecological footprint. TFR will need to drop from the existing (2020) TFR
of 2.448 (Macrotrends, 2020) to a replacement level fertility of 2.1 TFR before
global population stops growing.
A
recent (July 2019) Lancet article projects that we will reach this TFR of 2.1
by 2064, with global population peaking at 9.7 billion (Vollset,
2020). While somewhat controversial, this article was novel in how it
broke down the factors driving population growth. This study team
determined that improvements in access to modern contraception and the
education of girls and women have progressed, in effect, ahead of schedule,
leading fertility to decline more quickly than previously assumed. Their
model has population declining to 8.8 billion by 2100 – some 2 billion lower
than some of the UN Population Division’s estimates.
When
interviewed regarding this Lancet article, the head of the UN Population
Division, John Wilmoth, characterized the bending of the global population
curve as a ‘problem’, and surmised that it is a problem that nations’ leaders
will intervene to avert (Gladstone, 2020). It appears that the United Nations
community has not yet made a connection between our failure to meet UN
Sustainable Development Goals (SDGs) and runaway population growth. Or
they, too, have been bamboozled by the cult of perpetual growth.
Interestingly,
there has been no discussion about how this already inevitable bending of the
global population curve might be accelerated. If it can happen by 2064,
why not sooner? The Lancet analysis clearly shows how access to modern
contraception and the education of girls and women can drive a decline in
fertility, to below replacement level. Thus, it provides a clear roadmap
to how this inevitable trend (e.g., the bending of the global population curve)
might be accelerated. How much investment in access to modern
contraception and the education of girls and women would be required (and in
which geographies) to accelerate this inevitable trend? However, this was
not the research question driving the Lancet article. Perhaps their
follow up work will help answer this question.
1.5 by 2030
Of
course, we are left to ask ourselves, if this curve is actually something of
our own making, and not some inexorable process handed down by the gods, what
should our collective goal be? If indeed, our planet’s carrying capacity
can support a mere 3 billion modern industrialized humans, as billions are now
racing to join the global middle class, then what TFR could get us to that
lower, more sustainable population plateau?
It is
important to note how small changes in complex systems can lead to profound
change, very quickly. And, given the urgency we face with climate change,
and the threshold of 1.5C temperature rise that climate scientists and
biodiversity experts have settled on as a line that should not be crossed, many
have concluded that 2030 is the time horizon by which carbon emissions must
end. Flattening the global population curve would not end carbon
emissions. However, bringing the population curve below replacement level
on the way to 2030 and beyond would certainly help alleviate the carbon burden
on our planet, along with the 9 other forms of human footprint currently
undermining our planet’s ecological carrying capacity.
Not
only could we accelerate the bending of the global population curve now, and begin
alleviating the population pressure on our planet on or before 2030, but
bringing the global TFR down to 1.5 would set us on a course to achieve to a
global population of around 3 billion much sooner than current projections
anticipate.
As
such, we should ask ourselves, what would it take to bring the global TFR down
to 1.5 by 2030? In truth, this is not that big a change. And again,
it would simply be the acceleration of an inevitable trend that we already
predict for later in the century. People need to remember that in many
urban areas around the world, a TFR of 1.5 or lower is the norm. Further,
all predictions indicate that a vast majority of humanity will move into urban
environments over the coming decades. Investing further in the humane, ethical,
and empowering strategies outlined by the Lancet report could bend the global
population curve by 2030, bringing global TFR to 1.5, and perhaps even help us
avert a temperature increase of 1.5C or more. Small, educated, prosperous
families living in urban communities would become the species wide norm.
Pick your challenge
When
faced with a challenging proposal, it is easy to throw up one’s hands, and be
overwhelmed by the difficulty of the task. However, we are already
challenged by calls for epic, planetary-scale policy initiatives intended to
bend the curve of carbon in our atmosphere and our oceans – which runaway
population growth only serves to exacerbate. Similar proposals seek to
bend the curves driving loss in natural habitat and biodiversity, fresh water
resources, and the diminishment of so many other elements of our world
ecology. Of course, runaway population growth is at the heart of all of
these exasperating trends. In a very real sense, bending the global
population curve makes the realization of so many of our goals so much more
plausible.
We
could educate more women more quickly. That is called education
policy. We could integrate more women into the workforce more
quickly. That is called labor policy, (micro-)
finance policy, and economic policy more generally. We could empower more
women more quickly, by investing in access to family planning technologies,
norm shifting media interventions, and civil society initiatives. We
could encourage small, educated and prosperous families. None of these
policies are controversial. Many of these goals are already called out in
our Sustainable Development Goals. But the order and sequencing with
which we undertake these policies matters. It seems clear that an 18th
SDG should be added, as a capstone, that calls for an end to the runaway
population growth that is undermining our accomplishment of the other 17 SDGs.
Perhaps
the 18th SDG should call for 1.5 TFR by 2030.
Empowering future generations
to save our planet and our species
Without
malice of forethought, we have exceeded our planet’s carrying capacity.
In doing this, we have put future generations in the crosshairs of ecological
catastrophe and human tragedy. But, we could very easily achieve a more
sustainably and equitably prosperous global society that enables everyone to
live the good life within our planetary boundaries. We could even do this
very quickly, through humane, ethical, and just policies. We must simply
stop acting as if population growth is some unfathomable process that humanity
could never craft to its own advantage, and to the benefit of the planet that
gives us life.
It is
entirely feasible to achieve a more just and sustainable planet – one where
small, educated and prosperous families think deliberately about their impact
on each other and the ecosystems that give them life. We need not force
future generations to embrace the fear and uncertainty posed by the ecological
calamity that awaits if we refuse to change. We need only build bridges
to the rest of our brethren, across the globe, to accelerate already inevitable
trends, and bend the global population curve by collectively investing in
humane, ethical, and empowering strategies that will leave our world and our
society better off than when we entered it.
Notes
[1] The fertility rate for World in 2019 was
2.458 births per woman, a 0.41% decline from 2018 (Macrotrends, 2020).
Clifford,
C., 2019. Elon Musk and Jack Ma agree: the biggest problem the world will face
is population collapse. CNBC Make It. [online] August 30. Available
at: https://www.cnbc.com/2019/08/30/elon-musk-jack-ma-biggest-problem-world-will-face-is-population-drop.html [Accessed 1 November 2020].
Cohen,
J.E., 1995. How many people can The Earth
support? New York: W.W. Norton & Company.
Gladstone,
R., 2020. World population could peak decades ahead of U.N. forecast,
study asserts. New York Times.
[online] July 14. Available at: https://www.nytimes.com/2020/07/14/world/americas/global-population-trends.html
[Accessed 17 November 2020].
Macrotrends,
2020. World fertility rate 1950-2020. [online] Available at:
https://www.macrotrends.net/countries/WLD/world/fertility-rate [Accessed 17
November 2020].
Ripple,
W.J., et. al., 2019. World scientists’ warning of a climate emergency. BioScience, 70(1), pp.8-12.
Tucker,
C.K., 2019a. A planet of 3 billion.
Washington, DC: Atlas Observatory Press.
Tucker,
C.K., 2019b. A planet of 3 billion by Christopher Tucker – book extract. World Economic Forum. [online] Available at: https://www.weforum.org/agenda/2019/09/christopher-tucker-planet-of-3-billion-book-extract-climate-change [Accessed 1 November 2020].
Volk,
A.A. and Atkinson J.A., 2013. Infant and child death in the human environment
of evolutionary adaptation. Evolution and Human Behavior, 34(3), pp.182-192. https://doi.org/10.1016/j.evolhumbehav.2012.11.007
Vollset, SE., et. al. 2020. Fertility,
mortality, migration, and population scenarios for 195 countries and
territories from 2017 to 2100: a forecasting analysis for the Global Burden of
Disease Study. The Lancet,
396(10258), pp.1285-1306. https://doi.org/10.1016/S0140-6736(20)30677-2