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The classic overshoot pattern relating population size to resources and healthOne of my very favourite quotes about population and ecology comes from an unnamed friend on the Internet:

Asking ,"How will we get enough food to feed this growing population?" is a lot like asking "How will we get enough wood to feed this growing bonfire?"
 

The point of the quote is that most people have the ecological cause and effect of food and population exactly backwards.  The real problem is not that a rising population requires more food, but that an increasing food supply drives populations ever upward. 

While this makes for a nice pithy quote, and is a useful idea on its own, the real situation is, as always, more complex than that.  I've recently been thinking about this idea, trying to fit it into a more comprehensive view of population growth that takes into account both human and non-human species. Unfortunately, in the process I've beaten the pith out of the original quote...

Food supply is, of course, one of several factors that combine to limit the population of any species. If the food supply is capped that naturally places a hard upper bound on the population. Other limiting factors seem to be predation, disease and behavioural changes (whether voluntary or instinctual). There may be others, but those look like the biggies. Environmental breakdown usually limits populations by affecting either the food supply or disease rates, so it's only a proximate cause of population decline. 

So populations have their own version of "Liebig's Law of the Minimum": if one factor proves limiting to population growth, it doesn't matter how permissive the other factors are. 

Consider a classic predator/prey dynamic, such as foxes and rabbits. As the fox population grows and predation increases then the rabbit population declines, no matter how much food is available to the rabbits. Then as the rabbit population declines the fox population stops growing due to the lack of food.  Simple stuff. Of course humans have no predators, so predation not a Liebig Minimum for us. 

If a lethal disease infects a population, it doesn't matter how much food there is, the disease establishes the limit. We humans have population-level disease under control, so that's not a limit for us either. 

By the way, some people think war could limit our population, but I seriously doubt that. A war, even a thermonuclear war, is just not big enough to permanently reverse our population trend. A war with a billion casualties (over ten times the size of World War II) would set our population back less than 15 years, though it might take longer than that to recover the loss. 

Thinking strictly of the human situation: our food supply is not capped at the moment; we have no predators; and we have no large disease problem. The only thing mitigating our population growth right now is fertility reduction due to behavioural change, whether it's through women's education, Virginia Abernethy's proposed fertility-opportunity mechanism, or the effects of increasing wealth proposed by the Demographic Transition Model. Behaviour changes are bringing down our overall birth rate, but not yet fast enough to keep our total population from growing. 

It's axiomatic that our population will keep growing until the global net birth rate drops to 0. The UN says that may happen within 40 years, at a population of 9 to 10 billion in 2050. I'd call that a "soft limit", as it doesn't require an increase in the death rate, just a reduction in our birth rate. 

A "hard limit" would be a factor that increases our death rates or lowers our average life expectancy.  Predation is not ever going to be a problem for humans, so the main candidates for possible "hard limits" are diseases and food supplies. 

Disease could become a limiting factor if we have a major pandemic, but it would have to be awfully big even major diseases like the Black Death and the Spanish Flu haven't stopped us before. It is possible for serious disease to get a foothold in our population, though.  We could, for example, experience a dramatic rise in a variety of lethal diseases if the social infrastructure that supports our medical system crashes. Collapses of urban sanitation systems in major cities could also do it, allowing the spread of cholera, dysentery and typhoid. However, we now know enough about the origins of disease to protect ourselves pretty well.  Given our recent record with potential pandemics, I'd say the probability of the world population being decimated by a disease (or even several) seems low. 

So that leaves the food supply as the primary threat. We are already in overshoot, and overshoot always brings down the food supply over the long term. The signs are ominous – declining ocean fish stocks, dropping soil fertility, losses of arable land and fresh water, rising fertilizer prices, hints of trouble in the constrained genomes of various food sources, etc. 

If our food supply is the major risk that humanity faces over the next 50 to 100 years, then we have to acknowledge a serious question.  Can we alter our food production practices enough by 2050 or so to establish an equilibrium between a behaviourally stabilized human population of 10 billion or so (given that it does in fact stabilize there) and the long-term productivity of the biosphere, all in the presence of climate change and the inevitable shift in our energy infrastructure as we are forced to move away from fossil fuels. 

Many very clever people are working on various aspects of this problem: the permaculturists, the locavores, Big Agribusiness (God help us), scientists of all sorts, some city planners, anthropologists and even Bill Gates

Will we win the race? How clever are we really? And how wise? I suspect we're going to find out fairly soon.

Source: http://www.paulchefurka.ca/Population%20Limits.html  
Related PlanetThoughts.org reading:
  If Nothing Else, Save Farming (Nov-24-2009)

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Comment by: StevenSALMONY (Steven Earl SALMONY) (Jul-7-2009)   Web site
Imagine for a moment that we are looking at an ocean wave, watching it move toward the shore where it crashes finally at our feet. The wave is moving toward us; however, at the same time, there are many molecules in the wave that are moving in the opposite direction, against the tide. If we observe that the propagation of the human species worldwide is like the wave and the reproduction numbers of individuals in certain locales are like the molecules, it may be inaccurate for the latter to be looked at as if it tells us something meaningful about the former.

Abundant research indicates that most countries in Western Europe, among many other countries globally, have recently shown a decline in human population growth. These geographically localized data need not blind us to the fact that the absolute global human population numbers are skyrocketing. The world’s human population is like the wave; the individual or localized reproduction numbers are like the molecules.

Perhaps a "scope of observation" problem is presented to everyone who wants to adequately understand the dynamics of human population numbers.

Choosing a scope of observation is a forced choice, like choosing to look at either the forest or the trees, at either the propagation numbers of the human species (the wave data) or localized reproduction numbers (the molecular data). Data regarding the propagation of absolute global human population numbers is the former while individual or localized reproduction data are the latter.

From this vantage point, the global challenge before humanity could be a species propagation problem. Take note that global propagation numbers do not vary with the reproduction data. That is to say, global human propagation data and the evidence of reproduction numbers of individuals in many places, appear to be pointing in different directions. The propagation data are represented by the wave; the reproduction data are represented by the molecules moving against the tide.

In the year 1900 world’s human population was approximately 1.2 to 1.6 billion people. With the explosive growth of the global human population over the 20th century in mind (despite two world wars, ubiquitous local conflicts, famine, pestilence, disease, poverty, and other events resulting in great loss of life), what might the world look like in so short a period of time as 41 years from now? How many people will be on the planet at that time? The UN Population has recently made its annual re-determination that the world’s human population will reach 9.2 billion people around 2050, and then somehow level off. No explanation is given for how this leveling-off process is to occur.

We can see that the fully anticipated growth of absolute global human population numbers is about 8 billion people for the 150 year period between 1900 and 2050.

Whatever the number of human beings on Earth at the end of the 21st century, the size of the human population on Earth could have potentially adverse impacts on the number of the world’s surviving species, on the rate of dissipation of Earth’s resources, and on the basic characteristics of global ecosystems.

For too long a time human population growth has been comfortably viewed by politicians, economists and demographers as somehow outside the course of nature. The potential causes of global human population growth have seemed to them so complex, obscure, or numerous that a strategy to address the problems posed by the unbridled growth of the human species has been assumed to be unknowable. Their preternatural, insufficiently scientific grasp of human population dynamics has lead to widely varied forecasts of global population growth. Some forecasting data indicate the end to human population growth soon. Other data suggest the rapid and continuous increase of human numbers through Century XXI and beyond.

Recent scientific evidence appears to indicate that the governing dynamics of absolute global human population numbers are indeed knowable, as a natural phenomenon. According to unchallenged scientific research, the population dynamics of human organisms is essentially common to, not different from, the population dynamics of other organisms.

To suggest, as many politicians, economists and demographers have been doing, that understanding the dynamics of human population numbers does not matter, that the human population problem is not about numbers, or that human population dynamics have so dizzying an array of variables as not to be suitable for scientific investigation, seems not quite right.

If I may continue by introducing an extension of my perspective.

According to the research of Russell Hopfenberg,Ph.D., and David Pimementel, Ph.D., global population growth of the human species is a rapidly cycling positive feedback loop in which food availability drives population growth and this recent, astounding growth in absolute global human numbers gives rise to the misperception or mistaken impression that food production needs to be increased even more.

Data indicate that the world’s human population grows by approximately two percent per year. All segments of it grow by about 2%. Every year there are more people with brown eyes and more people with blue ones; more people who are tall and more short people. It also means that there are more people growing up well fed and more people growing up hungry. The hungry segment of the global population goes up just like the well-fed segment of the population. We may or may not be reducing hunger by increasing food production; however, we are most certainly producing more and more hungry people.

Hopfenberg’s and Pimentel's evidence suggests that the magnificently successful efforts of humankind to increase food production in order to feed a growing population has resulted and continue to result in even greater human population numbers.

The perceived need to increase food production to feed a growing population is a widely shared and consensually validated misperception, a denial both of the physical reality and the space-time dimension. If people are starving at a given moment of time, increasing food production cannot help them. Are these starving people supposed to be waiting for sowing, growing and reaping to be completed? Are they supposed to wait for surpluses to reach them? Without food they would die. In such circumstances, increasing food production for people who are starving is like tossing parachutes to people who have already fallen out of the airplane. The produced food arrives too late; however, this does not mean human starvation is inevitable.

Consider that human population dynamics are not biologically different from the population dynamics of other species. Human organisms, other species and even microorganisms have essentially similar population dynamics. We do not find hoards of starving roaches, birds, squirrels, alligators, or chimpanzees in the absence of food as we do in many "civilized" human communities today because these non-human species are not annually increasing their food production capabilities.

Please take note that among tribal peoples in remote original habitats, we do not find people starving. Like non-human species, “primitive” human beings live within the carrying capacity of their environment. History is replete with examples of early humans and more remote ancestors not increasing their food production annually, but rather living successfully off the land for thousands upon thousands of years as hunters and gatherers of food.

Prior to the agricultural revolution and the production of more food than was needed for immediate survival, human numbers supposedly could not grow beyond their environment’s physical capacity to sustain them because global human population growth or decline is primarily determined by food availability. Looked at from a global population perspective, more food equals more human organisms; less food equals less human organisms; and, in one and all cases, no food equals no humans.

Thank you.

Steven Earl Salmony

AWAREness Campaign on The Human Population, established 2001

http://sustainabilityscience.org/content.html?contentid=1176


  
Comment by: auntiegrav (auntiegrav) (Jul-5-2009)   

Oh, I was listening carefully. I just didn't state my exaggerations properly to fit the academic anal-retentiveness of published works.

The 30/70 split of vertebrate SPECIES is even more in my favor, and I knew that but didn't elaborate. Humans are not so adaptable as we tell ourselves, since we believe things too easily. We believe that we are invincible and that we can modify the environment. That history is based on local effects, not global. Now that we HAVE done a global modification (by ACCIDENT, not intent: big difference), we are more likely to depend upon our failed imaginary intentions to try and 'save' ourselves, usually making things much much worse (For example, trying to 'sequester' CO2 under the ocean and then triggering seafloor quakes and releasing even more methane).

Yes, I assume that everyone else makes the wrong assumptions BECAUSE THEY DO. I also make wrong assumptions, but I also have a lot of experience with making the RIGHT ones when it comes to science and technology and especially, seeing where belief in mathematics is folded up as some kind of origami-looking logic that is really only based on belief in the folding, not the details of the numbers.

It isn't a 'scientific' model that predicts the rise. It's a natural occurrence on another planet.

Sorry for the verbosity and the despotic attitude. It's the mercury in my blood, teeth, and decaying nerves that makes me a little bit misanthropic these days: or maybe it's the lack of vitamins in the food I buy. Whichever, it doesn't help things and I'll leave again for a while before you have to ask me to.
Keep up the good work, Dave. Just don't believe anything you think you should. Nature doesn't have a "should" button. It only has "go", not "stop". Humans invented the "stop" button, and like everything else they invent: it doesn't always work.
  
Comment by:  PT (David Alexander) (Jul-5-2009)   Web site

The 30% / 70% split of vertebrates was the number of species surviving vs those disappearing, not the number of individual animals (including humans) in the total world population of animals. It was clearly stated in the article, so it is important to read source materials carefully.

The survival of humans under extreme conditions may indeed mean that only a few million people will survive at the low population point, and they would live in poor conditions, but I consider it unlikely that humans would completely disappear, due to adaptability.

It is unlikely that the global environmental situation will be worse than the Permian age (for example, I have not heard any scientific model that predicts that 100 degree rise (F or C?) that you predicted.

AG, you seem inclined to assume that everyone else makes the wrong assumptions and conclusions. You are not the only person who puts valid ideas together, and your ideas in their extremity may well miss out on the future reality. Listen more carefully please before responding.
  
Comment by: auntiegrav (auntiegrav) (Jul-5-2009)   

First, a correction: I wanted to say that we shouldn't think of the CO2 as a 'trigger' so much as a valve: the more we open the valve by dumping CO2, the more the methane pipe is opened up. The CO2 is rising exponentially, and it is as though the valve was opened a little (10%?) in the past, then pushed closed by plants and ocean algae that reacted to the increased CO2 after a while. Now, we have opened the valve to FULL ON DUMP, which I think is probably more than the plants and algae will ever be able to handle, thus creating a Venus-like situation.

"Of course we humans are likely to arrange to be in the 30% surviving."
We are more likely to die by the billions from plagues and wars and famine, leaving a few to possibly survive, but there is little possibility that 6 billion people are going to be the 30% surviving life forms. The most likely to survive will be, as in the Permean, very small bodied and scavengers that reproduce with multiple offspring very quickly and with short lifespans to allow for fast evolution.
  
Comment by:  PT (David Alexander) (Jul-5-2009)   Web site

I think people see it as their effort to survive and prosper. The definitions of "survive" and "prosper" both need to be looked at closely.
  
Comment by: ausearth (ausearth) (Jul-5-2009)   Web site

What gets me is this race.
What are we racing for?
  
Comment by:  PT (David Alexander) (Jul-4-2009)   Web site

The worst scenario for environmental change was the Permian extinction of 250 million years ago. It was about 19C (~10F) degrees hotter than today, with an atmosphere containing increased methane. However, it seems that only about 70% of land vertebrate species were made extinct (see Wikipedia).

Of course we humans are likely to arrange to be in the 30% surviving.
  
Comment by: auntiegrav (auntiegrav) (Jul-3-2009)   

Oh. I thought you knew....

We'll all be dead and the climate is going to be around 100 degrees hotter than it is now.
That is, of course, if we compare the CO2 trigger level with the last total effect after a CO2 event. Even the worst climate doomsayers (other than me) don't use the very mathematics and core data that they purport is going to somehow miraculously NOT keep exponentially triggering methane releases, additional CO2 releases, and accelerated icemelt.
In other words, everyone talks about the science of climate change but nobody wants to actually apply the real data and tell us the bad news.
There's always 'hope'! ;-)
  
Comment by:  PT (David Alexander) (Jul-3-2009)   Web site

Yes, but I am talking about what happens 100 years or 200 years AFTER all that.
  
Comment by: auntiegrav (auntiegrav) (Jul-3-2009)   

The ecosocial system of systems is dependent upon a lot of technical factors that require a certain level of overhead support. If the ecosocial decays beyond a certain point, then it collapses under its own weight. Much like the airline industry requires a minimum amount of activity to support the inspections and overhauls and terminals. If they start to decay, then people stop going to the grungy terminals, maintenance drops off, and more cuts don't improve the situation. As the prices for energy got higher, our economic social system butted up against a wall. We have only begun to see the economic failures.
The current levels of populations (especially in developed countries) are on very shaky support columns right now: Cheap food, cheap energy, cheap water, cheap fire protection, cheap vaccinations and cheap government.
The money that should have been spent on real goods and localized ecosocial supports has been spirited away by financial 'instruments' and can't be brought back because the resources just aren't available to rebuild them.
People have to stop thinking that they need jobs, cars, government, etc.
Meanwhile, as the support structures for high population centers fail, we will see how randomness really works. One place might have a revolt, another might have starvation deaths, and yet others may have epidemics or government crackdowns, but in the end, the prosperity of waste will fail.
  
Comment by:  PT (David Alexander) (Jul-2-2009)   Web site

I agree with you, BC, and I would add one more thing with which I think you would agree: long-term, we may stabilize on an improved more sustainable way of life, and eventually rebuild the ecosocial environment. That could be 100 or more years away, but it is the end goal of a world that recovers from the spike of fossil fuel addiction of the last 200 years.
  
Comment by:  chefurka (Bodhisantra (Paul) Chefurka) (Jul-2-2009)   Web site

I expect that the cumulative "drag" imposed by post-peak energy conversion, regional social dislocations and ecological impacts of various kinds will show up as a slowdown in the population growth rate over the next five to ten years.

I don't think we'll see a population crash starting in 2020 as I did a few years ago, but keeping the human population higher will result in increased deterioration of other aspects of the human ecosocial environment. I use the term "ecosocial" to indicate that I'm talking about the human social environment as well as just the natural environment we're all used to hearing about.

I now see it this way: We could save the quality of the ecosocial environment by reducing human numbers, or we can save human numbers by reducing the quality of the ecosocial environment. What we will get, as usual, is a combination of the two. Human numbers will begin to fall due to a deterioration in ecosocial conditions, but not fast enough to keep the landscape from deteriorating further and faster than it already has.
  
Comment by: City Worker (Jul-1-2009)   

That great comparison of wondering how we can feed the growing population to wondering how we get enough firewood to feed a growing bonfire put into words the problem I’ve known is there but couldn’t quite verbalize. I would add the problem I’ve been subconsciously thinking of: How can we switch from fossil-based fuels to renewable energy quickly and efficiently enough so the world’s population can continue to grow exponentially and leave us with more bonfire-type problems?

  
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About author/contributor Member: chefurka (Bodhisantra (Paul) Chefurka) chefurka (Bodhisantra (Paul) Chefurka)
   Web site: http://www.paulchefurka.ca/

Member: chefurka (Bodhisantra (Paul) Chefurka) I am a Canadian ecologist with a passionate interest in outside the box responses to the converging crisis of industrial civilization.

The crisis of civilization is not simply a convergence of technical, environmental and organizational problems.  These are symptoms that are themselves being driven by a philosophical and perceptual disconnection so deep that it is best understood as a spiritual breakdown.  The disconnection goes by the name of Separation.

Our sense of separation is what allows us to see ourselves as different from and superior to the rest of the apparently non-rational universe we live in.  In this worldview the complex mutual interdependence of all the elements of the universe is replaced by a simple dualistic categorization:  there are human beings, and everything else in the universe—without exception—is a resource for us to use.

The only way to keep this planet, our one and only home in the universe, from being ultimately ravaged and devastated is to change our worldview and heal our sense of separateness.  Unless we can manage that breathtaking feat all the careful application of technology, all the well-intentioned regulations, all the unbridled cleverness of which we are so proud will do little to delay the final outcome, and nothing whatever to prevent it.

My desire is to find ways to heal that sense of separation, with the goal of helping us prepare for ecological adulthood.

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