The Computed Limit of Human Population
- Human population hit 7 billion people in December-2011. But the
effective population of earth should include the sum of "number of humans" and
"beasts of burden" and "air-breathing machines".
Remember that an automobile consumes more O2 (oxygen) and energy in one hour than its owner would
consume in 21 days. Now just think
about how much oxygen is consumed by the world wide population of boats
(tankers to cruise liners), planes, locomotives, farm equipment, 18-wheelers, automobiles, etc.
- Atmospheric O2 levels
have been falling ever since scientists began continual measurements in 1990. This is
due to the fact that atmospheric O2 is combined with C (carbon) to
produce CO2 (carbon dioxide) during chemical combustion as well as animal respiration. Even though CCS (carbon capture and storage) technology promises to
reduce CO2 emissions to the atmosphere by pumping CO2
underground, O2 levels will
continue to fall.
- There simply isn't a sufficient amount of photosynthetic life on
Earth to compensate for all the fossil fuels being burned by humanity.
Fact: Oceans, plants and animals emit about 780 gigatons of carbon
annually, and absorb nearly all of it. Human activities emit 29 gigatons
of carbon per year but absorb almost none of it (so it ends up in the
atmosphere). We can see this principle in action through the
which indicates a constant growth of atmospheric CO2 ever since
measurements began in 1958. More update-to-date atmospheric measurements
can be seen at
Did you notice the small "sine wave"
oscillating on the rising line? This annual fluctuation in CO2
is caused by seasonal variations in "carbon dioxide uptake" by land
plants. Since many more forests are concentrated in the Northern
Hemisphere, more carbon dioxide is removed from the atmosphere during
"Northern Hemisphere summer" than "Southern Hemisphere summer".
- Humanity (homotechnologicus?) is reproducing too quickly:
- Pick "your" preferred starting date
before thinking about our current problem:
- Abrahamic religions teach the world is ~
years old (starting population: one mating pair)
- Science provides these dates for your
- the current mammalian growth spurt begins
65 million years ago after an asteroid strikes Earth at
Chicxulub causing the dinosaurs to become extinct.
- modern humans first appear in the fossil record
200,000 years ago
- the current human growth spurt begins
ago after the end of the ice age (estimated population: between 5 and 10 million)
- Despite disease, war, and natural calamities, human population
reaches 1.5 billion in 1900.
This required many thousands of years.
- Despite disease, war, and natural calamities, human population
billion in 1999. This required only 99 years.
- So in 99 years, humanity repeated four times what
all previous history to do only once. Clearly, the current
human population (which is still growing at a rate of 1 billion
every 12 years) is too large and will soon
outstrip planetary resources. Even if we destroyed all our machines and
attempted to live like the
there are still too many of us. In order to support the current
population humanity will need to shift to
non-combustible renewable energies. Humanity will never
completely abandon fossil fuels and here are a few (of many)
- powering large machines like airplanes, ships, tanks and
heavy construction equipment, farming equipment, 18-wheeler
- starting point for
(how will we produce fertilizers if we use all fossil fuels in
- starting point for plastics
It all started by "Thinking
about Communicable Disease"
Influenza articles like these...
tell us that the Influenza Pandemic of 1918 was triggered by soldiers living in close proximity during
World War I. British medical archives tell us that an unknown disease (now known as
The Flu) started in 1915 and
then returned in 1916 and 1917. Apparently diseases often reach
pandemic proportions after three iterations.
I started thinking that communicable disease would certainly exterminate all of
humanity if we lived in similar proximity to World War I soldiers,
and I wondered what that
number would be. But all of humanity can't live like soldiers because we need
(at the very minimum) to "set
aside farm areas to provide us with food" and "industrial areas to provide us
with clean water while processing our detritus". While it is true that tall
buildings allow urban
peoples to live more densely than field soldiers, human population
will ultimately be limited by the area of land required to support life.
And I wondered what that number
- When you compare any two lines (e.g. "0.6 hectares" to "0.7 hectares")
there does not seem to be a safe margin of error. All you would need is one
bad agricultural year to nudge humanity over the top.
- Many human societies require beasts-of-burden (horses, oxen, elephants)
for farming and/or transportation. Each one of these larger animals require
agricultural land to support their biological needs so the Maximum
Supported Population tabled above should include the total of
"humans and domesticated animals". In this case humanity may have
already exceeded Earth's
- Not every society on the planet is using western
agricultural techniques -AND- climate change is limiting agricultural
productivity worldwide. I think it is safe to say that some projections
showing humanity successfully growing to nine billion are just a marketing fantasy.
billion may be out of the question as well. If we ignore these risks, I am
fairly certain that nature will produce some nasty diseases to limit our efforts. Perhaps the civilized
thing to do is to accept seven billion as an upper limit with an intention of
shrinking back to six billion or lower.
- Work published by
uses different numbers which require urgent action.
- For example,
his calculations state that the world
average amount in 2007 was 2.1
global hectares per person.
Quote: For 2007, humanity's total
ecological footprint was estimated at 1.5 planet Earths; that is,
ecological services 1.5 times as quickly as Earth can renew them
- estimated population in 2007:
- population in 1999 was 6 billion
- population grows ~ 83
million per year
- total = 6 billion + ((2007-1999) * 83
- total = 6 billion + 664 million
- correction factor for unity (where 100% of Earth's resources can
- target human population:
- 6.664 x 0.666 = 4.42 billion
- The typical U.K. citizen
requires 4.9 global hectares per person
- The typical American requires
8.0 global hectares per person
- for everyone on the planet to have the same quality of living as
an American, total population size must be reduced below one billion
- Proceeding forward humanity must do one or more of the following
- richer countries need to lower their standard of living
- families need to reduce size
- individuals need to delay reproduction
(the population clock is unnerving)
Current Official Population Densities (2011-12-29)
This table provides a starting point for comparative purposes (note: I'm not
sure if they are using total area or agriculturally usable area).
Videos (to learn more)
Unit Conversions (and other stuff)
Caveats (prompted by a few emails I've already received
about this page)
- one "square kilometre" is equivalent to "one million square metres" (1,000 x 1,000 =
- two "square kilometres" is only twice as much (2 million square metres)
- an area "two kilometres square" is equivalent to "four million
square metres" (2,000 x 2,000 = 4,000,000)
of Biological Productivity
C3 Photosynthesis (efficiency drops as
optimum ranges for photosynthesis in c3 and c4 plants
:: Gross photosynthesis vs. Net photosynthesis
This story on NPR's Science Friday radio program
contained the following quote from Lester Brown:
- Quote: How do plants deal with increases in
temperature? During the process of
transpiration, plants lose water through tiny holes in their leaves
called stomata. Because the water
evaporates from the surface of the leaf, transpiration helps plants
stay cool, in the same way sweating keeps humans cool. So the process of
plants losing water through their stomata prevents overheating of the
plant. Global warming is also projected to bring less precipitation or
increased drought conditions in many parts of the world. How do plants
deal with a lack of water? When less water from the soil is available,
the plant closes the stomata on its leaves so water doesn't escape from
the plant. Unfortunately, closed stomata don't let in
carbon dioxide (CO2) needed for
photosynthesis and plant growth becomes stunted. The plant must now
choose between keeping its own water (stomata closed) and gaining food
through photosynthesis (stomata open). At the point when the plant
cannot survive any more without food, it will be forced to open its
stomata, letting its own water escape. The plant, which is fighting to
survive, becomes wilted or withered.
- Quote: Daytime temperatures up to 86 F are
beneficial for corn plant photosynthesis. Anything above 86 F for a
sustained amount of time can foster disease development, cause stress
during grain fill and exacerbate ear rots
- Quote: for each 13 F increase in [night-time]
temperature, respiration rates may double. During this time the plant is
using more of the sugars produced by photosynthesis for its own
maintenance instead of growth
Further Research (C4 Photosynthesis and CAM)
My Interim Summary:
- Many online articles seem to confuse and/or contradict each other.
Putting what I have read so far into technical terms:
- All plants employ the
(a.k.a. Calvin–Benson-Bassham cycle)
employ the simplest photosynthesis processing design and make up 85%
of all the plants on Earth
- C4 plants build on the C3 design by employing a chemical pre-processor as a
front-end to the Calvin cycle.
build on the C4 design by doing additional molecular
pre-processing (like inhaling CO2) only at night.
- supporting Wikipedia articles:
- The 10-percent-per-degree
drop in photosynthesis (see above table) appears to apply only to
C3 plants like
wheat, rice, barley and oats. But there is a catch...
- Photosynthesis in C4 plants
like maize (corn), sugarcane, sorghum, and amaranth, operates at a fairly
constant level until the temperature hits the limit value (still 86 F
for corn) when the whole process abruptly
halts. There is no magic here and these plants can still wilt if the
temperature stays too high for too long of a period.
Daytime temperatures up to 86 F are beneficial for corn plant
photosynthesis. Anything above 86 F for a sustained amount of time can
foster disease development, cause stress during grainfill and exacerbate
ear rots [snip] High daytime temperatures can result in corn plants
having lower net photosynthetic energy and fewer sugars available for
corn kernel development. When nighttime temperatures also are high, corn
plants expend more sugars gained during daylight hours on nighttime
maintenance respiration. Ideal nighttime temperatures during grainfill
range between 60-65 F.
like pineapple and cactus, have adapted to higher temperatures but appear to grow
slower (would it be accurate to suggest "more cautiously?"). For
example, pineapple plants only flower every two years.
- As far as agricultural productivity is concerned, C3 plants
outperform C4 plants at normal temperatures. C4 plants
have an additional front-end processor which requires additional energy to operate.
(what was that old adage about "no free lunch"?)
- Quote: Plants which use only the
Calvin cycle for fixing the carbon dioxide from the air are known as
C3 plants. In the first step of the cycle CO2 reacts with
RuBP to produce two
3-carbon molecules of 3-phosphoglyceric acid
(3-PGA). This is the origin of the designation C3 or C3 in
the literature for the cycle and for the plants that use this cycle.
[snip] About 85% of plant species are C3 plants. They include the cereal
grains: wheat, rice, barley, and oats. Peanuts, cotton, sugar beets,
tobacco, spinach, soybeans, and most trees are C3 plants. Most lawn
grasses such as rye and fescue are C3 plants. C3 plants
have the disadvantage that in hot dry conditions their photosynthetic
efficiency suffers because of a process called
photorespiration. When the CO2 concentration in the
chloroplasts drops below about 50 ppm, the catalyst
RuBisCO that helps to fix carbon begins to fix oxygen instead. This
is highly wasteful of the energy that has been collected from the light,
and causes the RuBisCO to operate at perhaps a quarter of its maximal
rate. The problem of photorespiration is overcome in
C4 plants by a two-stage strategy that keeps "CO2 high" and
"oxygen low" in the chloroplast where the Calvin cycle operates. The class
of plants called
C3-C4 intermediates and the
CAM plants also have better strategies than C3 plants for the
avoidance of photorespiration.
- C4 examples: corn, sorghum, sugarcane and millet
- Quote: Maize (corn to the Yanks) to the rest of the
world, is a C4 grass. The C3 and C4 compounds aren't really all that
important, but any introductory plant physiology text will explain it. The significant fact about C4 plants is that
they are designed to grow in some pretty nasty climates. C4 metabolism,
Crassulacean Acid Metabolism (CAM), allows growth in deserts, on
mountains, tundra, etc. The poor C3 plants must necessarily capture and
subsequently incorporate their CO2 while the sun shines, so they open
their pores to get the CO2 during the day; the heat and wind
dries them out and they die. Those clever C4 plants, however, open their
pores at night and capture the CO2 when the air is cooler, so they won't dry out.
The next day (with pores closed), they use the light to incorporate the
CO2. C4 metabolism is a more expensive [energy-consuming] physiological
process than the C3 metabolism, but it allows the C4 plant to capture
more CO2 overall than C3 plants. If you put a C4 (corn) in a sealed
chamber with a C3 (potato), the C4 will suck up all the CO2, and the C3
plant will wither and die.
World Losses in Productivity (is it one degree Fahrenheit or Celsius?)
I have always been looking for publications which would say that an overall
10% loss is due to an increase of one degree
Fahrenheit or one degree Celsius
but have had no luck to date.
Considering all these points:
- The C3 Photosynthesis Table above was published using
- In a warming world, some bands of C3 agriculture may shift a little
farther north in the north (or a little farther south in the south) where
they will encounter more warmth but less sunlight.
- C4 plants are able to survive slightly higher temperatures
- C4 agriculture may be impractical or impossible to introduce intro areas
just vacated by C3 farms (if pineapple farms were practical in the American
south or south-west then wouldn't we already have seen them)
- Algae performs a lot of
photosynthesis in the oceans
I am going to speculate that Celsius is correct figure
when considering world-wide losses in biological productivity.
Flowering of Rice (blocked at high temperatures)
- Quote: High percentages of spikelet sterility occur
if temperatures exceed 35�C at anthesis (the maturing of the stamens) and last for more than 1 hour
- Quote: Rice becomes sterile if exposed to
temperatures above 35 degrees for more than one hour during flowering
and consequently produces no grain
- Quote: The objectives of this study are to compare
the floret sterility induced by a high temperature given in the daytime
during the flowering period among nine japonica rice varieties, and to
clarify the mechanism of the high-temperature-induced sterility. Nine
japonica rice varieties were subjected to 35.0, 37.5 or 40.0 degree C day-
temperature conditions (1000-1600) for six consecutive days using
sun-lit phytotrons, and the percentage of fertility, pollination and
germinated pollen grains on the stigmas were examined. The temperature
that caused 50% sterility varied with the variety, and a difference of
approximately 3.0 degree C was observed between the most tolerant and
susceptible varieties. Under the 37.5 degree C day-temperature condition,
the percentage of florets with 10 or more germinated pollen grains was
roughly coincident with the percent fertility, but under the 40 degree C
day-temperature condition, it was higher than the percent fertility.
Many of the florets with less than 10 germinated pollen grains had less
than 20 total pollen grains on their stigmas under both temperature
conditions. From these results, we concluded that sure pollination under
high-temperature conditions is an important factor and that the
high-temperature tolerance of the processes following pollen germination
is also required for fertility under excessively high temperature
- Quote: Rice is grown mainly in tropical and
subtropical zones, and a high temperature at flowering can induce floret
sterility and can limit grain yield. Since the 1980s, an increase in the
concentration of greenhouse gases, such as carbon dioxide, in the
atmosphere is thought to have been responsible for increasing the air
temperature. Amongst other things, global warming is expected to result
in the occurrence of high temperature induced floret sterility in rice.
Tree growth is slowed by heat
- the idea for this section was inspired by material on page 39 of issue 28-January-2012 of
- Key points:
- all plants, including trees, employ both photosynthesis and
photosynthesis collects energy by converting sunlight, water (H2O) and
into glucose (C6H12O6)
respiration reverses the process by extracting energy from
glucose by burning it with oxygen. Just as is animals, this
chemical process takes place in cell organelles known as
This energy is used for both maintenance and growth.
- tree canopies retain moisture to enable leaf temperatures to remain cooler than
ambient air temperature (see the
chart above showing the optimum average temperature for
photosynthesis being 76 F or 24.4 C). Believe it or not, this canopy is
by trees engaging in
(when sufficient water is available).
- when leaf temperatures get too hot, leaves close their stomata in order
to conserve moisture. At this point, photosynthesis stops but
- respiration also continues at night when photosynthesis is not possible.
- the amount of respiration (day or night) is proportional to the
- The highest amounts of respiration occur during the day
- Warm nights mean more respiration (consumes more glucose and
- Cool nights mean less respiration (consumes less glucose and
- Cold-to-frozen nights mean no respiration (dormant)
- When not in a dormant phase...
- a tree will only grow when energy requirements (respiration) are
lower than energy
- a tree will not grow when energy requirements (respiration)
closely match energy
- a tree will die
when energy requirements (respiration) are not equaled by energy
- For a short time, a healthy tree...
- with sufficient resources might grow more leaves
(to increase energy
- with insufficient resources might drop leaves (to drop energy requirements)
- To learn more:
- The "10% rule of thumb"
Plants are able to "fix" about 10% of the solar energy that
reaches plant surfaces (usually less, however). "Fixing" means
converting solar energy into chemical energy (sugars). Organisms
that consume plants, are able to extract about 10% of the energy
stored in the plant. Organisms that consume other consumers can
extract only about 10% of the energy stored in their prey. These
levels of energy consumption are called "trophic levels." Energy
flow through an ecosystem (large or small) is a key life
process. Threads of energy transfer are called "food chains."
Food chains also include the transfer of chemicals other than
sugar. Many nutrients, amino acids, and other compounds are
digested and recombined by consumers along any particular food
So what does this mean for trees?
- A healthy plant requires ten times more energy to grow
properly than it does to maintain its life while under
stress but not dormant.
- Humans don't eat trees but if humans want to rely upon
trees to clean up the atmosphere (increase oxygen via
photolysis; decrease carbon-dioxide via photosynthesis) then
each person on the planet had better plant (and maintain) ten trees. Obviously a family of four requires
Oceans cannot be relied upon to pick up the slack
- Just like a warming beer begins to fizz, warming oceans release their
dissolved gases including oxygen (there is more oxygen found in cold water
which is why the best trout and salmon come from polar waters) and CO2.
This is an indication that warming oceans will be far less productive in the future.
- Since Jellyfish are able to out-compete other species in oxygen-poor
water (probably reminds them of environmental conditions 550 million
years ago), they are increasingly a large proportion of biomass netted (and thrown back) by Japanese
fishermen. Believe it or not, the amount netted is related to the lunar
- After movies like Jaws and Anaconda
people have a new found respect for sharks and snakes. But it turns out
that Box Jellyfish (Irukandji)
kill more humans each year than all the other animals combined. On top
of this fact, the death is usually misdiagnosed as either a heart attack
or stroke which means that the official recorded death statistic is way
- Ocean levels are rising. The question here is this: are levels due to
melting polar ice or the thermal expansion of water? Many scientists say it
is about half-and-half.
Have We Already Passed the Tripping Point?
Talking Point #1
Some people tell me "humanity has nothing to worry about because CO2
is good for plants". Supposing that this statement isn't a naive over
simplification then we must ask: when can we expect plants to
react to the excess CO2?
Referring to the Keeling Curve
for a moment, it looks like CO2 has been on a constant rise ever since Charles Keeling started
taking official measurements in Hawaii starting in 1958. The rising line looks
fairly straight and you would have thought we might see the results of an explosion of plant life to
compensate for all the additional CO2. More update-to-date
atmospheric measurements, charts, and datasets can be retrieved from
NOAA's GMD (global
monitoring division) site.
(Calculation for 2011: 391/315=24% increase over 53 years)
Maybe higher atmospheric temperatures (due to higher CO2
levels) are preventing plant life (at least C3 plant life) from exploding into
the role of "environmental savior" because the atmospheric temperature chart
seems to have grown continually since 1878 when the International Meteorological
Society began daily world-wide measurements. One thing that is certain is this:
additional deforestation by humans probably hasn't helped. Especially if it was
done by slash-and-burn techniques.
Talking Point #2
Some people tell me "higher levels of CO2 will
force plants to grow". This is a gross oversimplification for
the following two reasons:
- Almost all biological systems are pull-based rather than push-based. For
example, a body-builder will lift weights to force his body to "require" more
dietary protein. This causes an increased amount of dietary protein to be pulled into the body
from the digestive system which, if you think about it, is outside the body.
Attempting to push-in nutrients does not induce muscle growth (but a lack of
it will be a problem if not enough is present when required).
- A grade-school explanation of photosynthesis tells the young student that "CO2
is converted into O2". Sometimes a very simplified chemical
formula is provided like this one:
+ H20 + energy = (CH2O) + O2
High-school biology classes
introduce more chemical details including a formula similar to this one:
+ 6H2O + photons = C6H12O6 + 6O2
College courses in molecular biology fill in the
intermediate steps which show that O2 is only liberated by
the photolysis of
water (the original research was done using radioactive tagging).
So rather than saying: During photosynthesis, "CO2
is converted into O2" it is more accurate to say "H2O
is split by photolysis into O2
and H with the O2
discarded to the atmosphere; later in the process, H is combined with
atmospheric CO2 to produce glucose"
So we now know that sunlight (input 1) and H20 (input 2) are more important than CO2
because the photolysis of water in Photosystem II (on the left-hand side of the diagram) powers the
Calvin Cycle (on the right-hand side of this diagram). We already know that
too much sunlight, or too much water, will kill a plant so pushing in
additional carbon-dioxide makes little sense (but each ingredient is
considered a limiting factor to maximum productivity). But because increasing atmospheric CO2
is driving up atmospheric temperatures, we can expect increased
evaporation. This will result in less bio-available water to plants.
A few more details |
The left-hand side of the diagram was previously known as
The Light Reactions but most publications this side of Y2K
refer to it as
- Light induces photolysis (splitting of water into hydrogen and
oxygen) which liberates an electron along with a small amount of energy
to power other chemical reactions (see:
transport chain for details)
- one liberated electron is used to bind phosphorous (+P) with ADP yielding
(the power transfer molecule of most biological systems including humans)
- energy is used to bind atomic hydrogen (H) to NADP+ yielding
transport hydrogen to the other side of the diagram)
- some energy is used to bind atomic oxygen (O) into molecular
oxygen (O2) which is released to the atmosphere
- observation: You might wonder why
Photosystem II is before Photosystem I.
These labels relate to the order in which they were discovered
and were not changed because this would conflict with previously
- The right-hand side of the diagram was previously known as
The Dark Reactions but most publications this side
of Y2K refer to it as
- hydrogen (from NADPH) is combined with atmospheric CO2
to produce glucose
- the whole thing is powered by converting ATP back into ADP
(which frees a +P to be used in the next turn if the cycle)
Speculation: to avoid a CO2 run-away effect, humanity may need to engage in
world-wide terraforming of Earth just to get the rising CO2 problem under
control. Fat-cat business men will try to make a buck out of this crisis but
this might be something that everyone on Earth will be pressed into to
doing just to save humanity and human culture (which Earth's biosphere couldn't care
Talking Point #3 - Fact: Atmospheric Oxygen is Falling
I recently stumbled onto this
at John Cook's Skeptical Science
site which states "Atmospheric O2
(oxygen) is decreasing by the same amount that CO2
(carbon dioxide) is increasing" and
here are two IPCC published charts documenting it.
Yikes! I think I made a
fairly strong case
at the top of this page for the area of
farmland being the main limiting factor to the human population but it now
looks like humanity is using more oxygen than is being replenished by photosynthesis.
The article also states "Atmospheric Oxygen is so abundant at about 20.9% (209,500
parts per million or ppm) that we are in no danger of running out". But I think
we need to realize that our planet has "turned a corner" which means humanity
cannot continue previous behavior.
it is true that 7 billion humans are busy inhaling O2 and exhaling CO2,
no one has mentioned the elephant in the room: automobiles. Like large animals
engaged in respiration, automobiles (which experts number at slightly over 1
billion) are responsible for a large amount (perhaps 20%) of O2
being converted in CO2. Really large machines like locomotives,
tankers, cruise ships, and jet air craft, consume way more O2
than a car, but there are far fewer of them compared to automobiles. So at the very
least, the automobile population needs to be included when computing the maximum population of human and large animals
at the top of this page. We all know that
humanity has no intention of giving up personal transportation
so I think I have
just convinced myself of the need for electric cars powered by renewable energy
from hydrological, wind and solar technologies.
- "ppm" vs. "per meg"
- Some scientists still do not realize that making information more
complicated will only confuse the layman while fuelling the arguments of
conspiracy theorists and climate-change deniers. Such is the case with
this IPCC chart which mixes two units ("ppm" and "per meg") on one graph.
- Represents "parts per million" but this label is somewhat
ambiguous since it assumes volume rather than mass (weight). Modern scientific texts (this side of y2k)
explicitly use the phrase ppmv (parts per million
- "per meg"
- In the mid-1980s, the
pumped atmospheric samples into tanks to act as a future reference
sample. Each year they make new measurements then compare the ratio of
oxygen to nitrogen between the two. They did it this way because if lab
equipment was modified in anyway, then both current and reference
samples would be treated identically each measurement cycle.
- Some scientist have published alternate material claiming that when
fossil fuels are burned, 3 molecules of Oxygen are lost for every increase
in Carbon Dioxide
Quote: It is roughly true that the oxygen depletion is
equivalent to a displacement by carbon dioxide. But it is not exactly
true. First, some of the carbon dioxide produced has been absorbed by
the oceans. This process involves inorganic chemical reactions which
have no effect on O2. Second, the O2:C combustion ratio of a fossil-fuel
depends on the hydrogen content. The ratio varies from about 1.2 for
coal, 1.45 for liquid fuels, and 2.0 for natural gas. Taking these
factors together, we are losing nearly three O2 molecules for each CO2
molecule that accumulates in the air.
the beginning of the industrial revolution we have removed .095% of the
oxygen in our atmosphere. True, that is only a tenth of one percent of
the total supply, but oxygen makes up only 20% of the atmosphere.
Parable of the Bacteria in a Bottle
Developed by Al Bartlett, professor of physics at University of Colorado
- You place a single bacterium in a nutrient-filled bottle at 11:00 am. It grows and divides into two bacteria at 11:01. These two bacteria each grow and divide into 4 bacteria at 11:02, which grow and divide into 8 bacteria at 11:03, and so on. (i.e., doubling time of 1 minute.)
- Bottle is full, nutrients gone, all the bacteria die.
- When was the bottle half-full?
Hover Mouse Here to View Answer:
- You are a mathematically-sophisticated bacterium, and at 11:56 you recognize the impending disaster. You immediately jump on your soapbox and warn that unless your fellow bacteria slow their growth dramatically, the end is just four minutes away. Will anyone believe you?
Hover Mouse Here to View Answer:
- Just before disaster strikes… a bacterial space program discovers three more bottles in the lab. With a population redistribution program, how much time do the 3 new bottles buy the colony?
Hover Mouse Here to View Answer:
- How does this apply to humanity?
- Despite the negative effects from two
world wars and numerous pandemics including HIV AIDS and Ebola, human population quadrupled between 1900
(1.5 billion) and 1999 (6.0 billion). Our current growth rate is
approximately one billion for every 12 years. We passed 7-billion in
December, 2011, and will probably reach 8-billion sometime in 2023.
While it is true that the growth rate as a percentage is falling, an
additional billion every 12 years is still constant growth, and humanity
is courting disaster.
- When human populations in Europe grew too large, nature cooked up
diseases like Typhus, Cholera, and the Bubonic Plague to limit our
numbers (some estimate that communicable disease wiped out between 25%
and 75% of the European population over a 500 year period). If human
population continues to rise, compromised immune systems (due to poor
nutrition), will enable a deadly repeat of what we've experienced
- Politicians and Economists don't seem to understand that constant growth (of even a percent or two) is not possible.
- The only other life-form on Earth which attempts to continually grow
is cancer although rodent populations come a
- If humanity follows this course then we are no better than a disease
on this planet attempting to out strip our resources.
- I am convinced that the Earth does not need us. Human civilization
could be totally wiped out and the Earth would not care in anyway. But
don't worry, humanity can probably rely upon humans
living in Polynesia to reboot civilization all over again (although it
may require another 11,700 years).
- Think twice about all this stuff the next time you hear anyone criticizing the government
for poor GDP (gross domestic product) or GNP (gross national product)
- Engineers would most likely advise humanity to move from a
"growth-model" to a "steady-state model".
French Lily Pond Riddle
This story is told to French school children to impart the power of
- One lily pad in a pond
- The next day it doubles: two lily pads
- The next day it doubles: four lily pads
- The next day it doubles: eight lily pads
- After 29 days, the pond is half filled
- One day later, the pond is full
- It required all of our history for humanity to reach 1.5 billion in
- It only required 99 years for humanity to reach 6.0 billion in 1999.
- So is humanity at step 5 of the lily-pond riddle, or step 6?
Video Lectures (to Learn More Details)
Free 10-minute video lectures from Khan Academy
A refresher on photosynthesis
A refresher on cellular respiration
Assertion: One U.S. Gallon of Gasoline
= energy needs of one human for 20.8 days
||1 Gallon of Gas = 125,000 BTUs
||Source: US Department of Energy
||3,400 BTUs = 1 KWH
||Source: US Department of Energy, Bonneville Power Mgt.
||1 Gallon of Gas = 37 KWH
||125,000 BTUs in a gallon of gas divided by 3,400 BTUs in 1 KWH
||Human work output in agriculture = 0.1 HP or 0.074 KW
||37 / 0.74 = 500
||1 Gallon of Gas = 500 hours of human work output
||37 KWH in 1 gallon of gas divided by human work output in
agriculture of .074 KW = 500
||500 / 24 = 20.8 days
Kitchener - Waterloo - Cambridge, Ontario, Canada.