Population
estimates for 2100 vary between 8 billion and 12 billion humans. The current
global population is 8.3 billion. The reality is that we don’t know what
technologies will be available in the future to mitigate and possibly even
reverse resource depletion, environmental destruction, and provide for all. A
new study says that reducing the Earth’s human population to 4 billion by 2200
is the best way to achieve sustainability. I do not think that I agree with
that premise. The authors of the paper note:
“Gently ending and reversing population growth and
moderating per capita impacts is a pro-nature and pro-human strategy.”
“It will ease pressure on natural resources, lessen
poverty in high fertility regions by way of smaller family sizes, reduce
pollution, reduce resource and immigration conflicts, and improve quality of
life in densely populated areas. A more modest population (e.g., gently easing
population to 4 billion by 2200) would protect Earth's natural heritage,
including its wild habitats, wild species, and its climate,” they add.
Just a few days ago, I
reviewed the ideas of a group of economists and researchers who concluded with
quantitative and qualitative arguments that we could support 12 billion people
by 2100 without too much disruption.
Population growth is
concentrated in the poorer parts of the world, especially in Sub-Saharan
Africa. The authors of the new paper believe that by giving women family
planning services and improving girls' educational opportunities, especially in
low-income countries, they could end population growth in those places and
induce population decline. There is data to back their arguments, and indeed,
in developing and especially in developed countries, there has been significant
stagnation of population growth and population decline. Thus, we know that with
these policies and others, the world’s population can be stabilized and perhaps
even decline a bit. The question is how much it should decline.
“When women are free to decide how many children to
have, fertility rates tend to fall toward replacement level or below, often
rapidly,” the study authors write.
The article about the study
in IFL Science notes the uncomfortable past of population control. Controlling
population smacks of eco-fascism, they note, and the failed ideas of biologist
Paul Erhlich and the forced sterilization and China’s “one-child” policy he
inspired are clear examples.
Below, the paper authors
assert their belief that economic growth is not sustainable. Here is where I
diverge. As long as we have a population where some are without basic
necessities and access to modern living standards, it is economic growth that
is the best means to get them to where they can achieve freedom from poverty.
We are already moderating per capita impacts and will continue to do so, and
likely accelerate that moderation. I agree, of course, that we can’t and won’t
continue to grow population forever, and the data indicates that it will peak
and perhaps decline a bit at some point in the not-too-distant future, as
models suggest. When population stabilizes and poverty is eliminated, there
will no longer be a need for economic growth, and that too can stabilize, but
not before that. The fact is, we don’t know what the level of population would
be to achieve that and still keep resources available for all, but I don’t
think dropping the population by half will be necessary.
“Ever-growing wealth and consumption are not
ecologically sustainable, and the sooner our societies grapple with this
inconvenient truth, the better,” they added.
“Our results suggest that ever-increasing levels of
population and resource consumption are not in the interests of future
generations, and not the way to sustainability. Helping population growth end
and gently and justly reverse, while also moderating per capita impacts, is our
best hope to secure a sustainable, desirable future worldwide,” the paper
continues.
The following graphs from the
report show strong correlations between population growth and loss of wildlife
abundance, energy use, and carbon emissions. The story is similar for
ecological footprint, freshwater use, mineral extraction, plastic production,
and pesticide use. However, one may also note that several of these graphs have
been stabilizing in recent years. Of course, they will continue to grow with
population growth until per capita use drops. This is true of energy use and
emissions as long as people still lack access to modern levels of energy and
electricity. We know this because per capita energy use and emissions have
stabilized in developed countries. Mineral extraction can likely support 12
million people by 2100, argued those economists and researchers I mentioned
earlier. Global per capita freshwater use has already stabilized, and per
capita mineral extraction and ecological footprints are beginning to stabilize.
There are also indications that per capita plastic production and pesticide use
are on a path toward stabilization.
As the table below shows,
only per capita mineral extraction and plastic production have exceeded
population growth between 1970 and 2020, especially plastic production. The
other variables have been growing more slowly than population growth. The
second table below shows that per capita ecological footprints and freshwater
use have declined during the period, while the others have increased. Carbon
emissions per capita are close to a point where they begin to decline.
The table below shows how
much per capita use of these variables would have changed if there had been no
population growth (presumably since 1970).
They also give future
projections to 2100 and 2200 under two UN fertility scenarios and one Institute
for Health Metrics and Evaluation (IHME) scenario, shown below, but I think
such projections are probably too speculative. Are they using today’s technologies
to predict? We have to assume technological improvements, and they are more
likely to enable far more sustainable resource use and reuse.
While I don’t entirely
disagree with the paper’s conclusion below, I think the 4 billion number is
rather arbitrary. It could easily be 6 billion, 8 billion, or 12 billion with
improvements in technology. If we could harness nuclear fusion for energy or develop
sustainable materials to replace plastic, or replace the need for many
minerals, etc., that could change those predictions considerably. Of course,
I’m being speculative too. Thus, I believe that projecting beyond, say, 2100,
74 years into the future, is not going to be very accurate or useful.
5 Conclusion
“Gently ending and reversing population growth and
moderating per capita impacts is a pro-nature and pro-human strategy. It will
ease pressure on natural resources, lessen poverty in high fertility regions by
way of smaller family sizes, reduce pollution, reduce resource and immigration
conflicts, and improve quality of life in densely populated areas. A more
modest population (e.g., gently easing population to 4 billion by 2200) would
protect Earth's natural heritage, including its wild habitats, wild species,
and its climate. Such a world is within our grasp.”
References:
Achieve
Sustainability by Easing Population to 4 Billion by 2200. Mark Keegan,
Anastasia Pseiridis, Philip Cafaro, Jane O'Sullivan, William Rees, Estelle
Monique Sidze, Lawrence Whitmore, Enrique J. Derlindati, Mohammad Mainul Islam,
Khaoula Houssini, and S. Irudaya Rajan. Sustainable Development. 26 July 2026. Achieve
Sustainability by Easing Population to 4 Billion by 2200 - Keegan - Sustainable
Development - Wiley Online Library
Halving
The Earth's Population To 4 Billion Is The Best Way To Secure A
"Pro-Human" Future, A New Study Argues: The world population is
currently 8.3 billion people. Can it continue to grow? Tom Hale. IFL Science.
July 28, 2026. Halving
The Earth's Population To 4 Billion Is The Best Way To Secure A
"Pro-Human" Future, A New Study Argues | IFLScience
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