According to the United Nations, the world population
reached 7 billion on Oct 31st, 2011, the Day of Halloween Day. And the honor of being the 7 billionth baby went
to a girl who was born in the Philippines (see a news
report and party photo.) If UN’s
goal was to sound the alarm (again) and draw attention to the concern about our
ever increasing world population, they have got my attention.
There have been continuing discussions by scholars, analysts,
and journalists of the recurring worry – how
much longer can the planet earth support its ever increasing population and how
many people can planet earth sustain. It turns out these questions are very
difficult to answer with certainty and the estimates vary widely with different
assumptions and extrapolations.
Nevertheless, the exact numbers is not nearly as important as the methodology
of the analysis and the few basics and boundary conditions.
To begin with, let us agree on why the population keeps growing
and what is required to keep it at a constant level. The answer to the question of “why” should be intuitive
and non-controversial: any system would be growing if the incoming rate exceeds
the outgoing rates in long enough time scale.
We experienced it frequently in our everyday life and observed when the
rates are not balanced. For example, we
saw our kitchen sink backed up when the drain was clogged; we encountered long
delays at bridges and tunnels during rush hours when arrival rate of traffic
exceeded the rate of what these conduits can clear. There is no difference for population: when
the rate of births is higher than the rate of death, we can expect the population
would grow, ignoring the time lag factor of life span for now.
How have we been doing lately regarding these rates? The frequently used technical term is the (crude)
birth rate (CBR) which is simply the number of births
in a given year for every 1,000 persons in a given region. If you go to Wikipedia and look up the List of countries by birth rate,
you can find that for instance, CIA World Factbook estimated in 2009, birth
rate by country/region ranged from the highest in Niger (a western Africa
country) at 51.60 (per thousand) to the lowest in Japan and Hong Kong at about
7.5, while U.S.’ CBR stood at 13.82 and India was at 21.6.
To make some sense of these numbers, we need to compare them
with the (crude) death rate (CDR) of
these countries. Death rate in Niger,
Japan, Hong Kong, U.S. and India were estimated by the same document at 14.83,
9.54, 6.76, 8.38, and 6.23 (per 1,000 people), respectively. In other words, there was an estimated net
increase of population of 37, 0.74, and 4.4 per 1,000 people in Niger, Hong
Kong and U.S. respectively and a net decrease of 2 per 1,000 people in Japan in
year 2009. Since U.S. had a population
about 300 millions, it simply says there was an estimated 1.3 million net
increase in population.
An alternate and intuitive way of looking at the growth rate
of our population is to consider the total fertility rate, which is the average
number of children born to each woman over the course of her life. The reasoning goes like this: if the average
number of female babies born per woman in her childbearing ages is exactly 1,
then the population would remain a constant since that female baby would
replace the mother, no more and no less. The equivalent technical term of replacement fertility rate is thus also
frequently used which is simply the average number of children, either male or
female, required to replace the mother. Once
we account for the skew due to chromosome difference (there are slightly more
boys than girls born due to the built-in bias in reproduction process in favor
of the Y chromosome) and the infant mortality, the replacement fertility is at about
2.1 births per woman for developed countries and more than 3.0 for many
developing and underdeveloped countries.
Niger’s fertility rate of 2009 was estimated to be 7.07 (according to
the CIA World Fact Book).
Some may argue that we should not worry since the world population
growth rate has been declining in recent years and has reached a very modest
rate of 1.1%. Ignoring issues of huge
disparities among regions and countries for the time being, should we be
worried or not? Professor Emeritus
Albert Bartlett of University of Colorado at Boulder had the following to say
about the reality of steady growth
and how most of us ignore it: "The greatest shortcoming of the human race is our inability to understand the exponential function." He was referring to our
failure in recognizing how explosive it really is of anything that grows at a
constant rate. Watch the lucid lecture he gave below, entitled Arithmetic, Population,
and Energy. It should convince you
with just the first 10 minutes of the videos that steady growth is scary unless
it happens to be your investment and bank accounts.
Now we can return to our original questions of how much longer can the planet earth support
its ever increasing population and how many people can planet earth sustain. We are going to focus on the 2nd
part of the question since we already have the ideas of the growth rate. If we have an estimate of how many people the
planet earth can sustain, we can easily estimate how long it would take for the
population to grow and hit that level with the given population increase rate and
various assumption like what Professor Albert Bartlett has demonstrated.
The big picture looks as follows. We can all agree that the minimum and most basic
resources for our survival are obviously food and fresh water (assuming air is
not an issue). It has been estimated that planet earth has
over 300 million cubic miles of water but only 3% of it is fresh water. Further, two third of the fresh water is in
frozen form such as ice cap and glaciers which is necessary to keep the earth cool
and sea level in check. In all, we have
about 3 million cubic miles of (mostly renewable) fresh water and only 0.3% (or
almost 10,000 cubic miles) of it is on the surface (in lakes, rivers, snows,
etc). The rest are underground and not
necessarily accessible.
You may or may not know what we drink directly is just a
tiny fraction of our total fresh water consumption. The dominant consumption of freshwater is
actually for food production – 70% of the fresh water consumption is for
agriculture. With today’s efficiency, we
need for example, 3,000 gallons or over 11 metric tons (11,000 Kilograms or
24,000 pounds) of fresh water to grow one bushel (about 25 kg or 56 pounds) of
corns. We need about 900 metric tons of
water to grow one metric ton of wheat.
And it takes 2,500 gallons or about 10 metric tons
of water to produce one pound of beef.
Some researchers have offered an overall
estimate that it takes in average about 3,000 liters (or 3,000 kg) of fresh
water to produce food of recommended daily dietary need for just one person. If you assume that fresh water (renewal)
cycle is in average 2 years (too short?), i.e., time takes after the
consumption of fresh water till it becomes available and is consumed again, and
that majority of fresh water supply is from surface, then with some simple arithmetics,
the earth should be able to sustain about 7.5 billion people with decent nutrition.
Now you can understand why there are
already so many starving people in the world given uneven distribution and
local overpopulations.
We haven’t even talked about the connected
issue of the availability of arable land and other limiting factors which are
required for food production. The fact
is China, India, and many countries have been busy buying and leasing land in
Africa to produce food for their domestic consumptions. This should give you a pretty good idea of
what is going on. We also have not gone
into the details of the assumption of the living standards for some of those
estimates. Obviously, there is a huge difference
in the per person consumptions of resources for U.S. and for countries like Niger. With all these considerations, Ross
McCluney
estimated in his article of How Many People
Should the Earth Support? that the planet earth
can support about 6 billion people if U.S. and Western European keep their
current level of prosperity and the rest of the world live like Mexicans. Obviously it is too late to debate that as we
already past the 7 billion milestone at the end of last month. He also estimated that the earth can support 20
billion people if everyone lives like Mexicans and 40 billion if everyone lives
like people in today’s northwestern Africa.
But would you be ok to live like that?
Along with the rich resources and information
compiled on the EcoFuture web site, one
finds two interesting quotes which still ring true today and worth repeating
here. One was by the late Isaac Asimov, a
famous biochemist and writer. In his Oct
1988 interview with Bill Moyer, he said: "...democracy cannot survive overpopulation.
Human dignity cannot survive it. Convenience and decency cannot survive it. As
you put more and more people into the world, the value of life not only
declines, it disappears. It doesn't matter if someone dies. The more people
there are, the less one individual matters." The other is a popular but un-sourced
quote by the late Robert McNamara who was the Secretary of Defense overseeing
the escalation of Vietnam War and former World Bank President. He supposedly had said: “Short of nuclear war itself, population
growth is the gravest issue the world faces. If we do not act, the problem will
be solved by famine, riots, insurrection and war.”
What McNamara was referring to have been happening in many
places at smaller scales including the ongoing Africa Horn as we speak. The “good”
news is if the problem is not addressed soon enough, it will be solved for us
anyway. Planet earth will continue on for
a very long time after you and I died, and with or without humans. The bad news is the solution is going to be
real ugly, much worse than the often criticized China’s one child policy. There will be conflicts, famines, wars, and
massive deaths as people will be fighting for the little remaining available
resources. Meanwhile the continuing deterioration
of the environment and climate change could only accelerate the downward spiral
and further reduce the available resources.
By then, it will be too late for
the occupants of earth to try to reverse it. What do you think we should do now?
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