Sunday, August 28, 2011

The population follows our production system

"On a global level, it is hardly a coincidence that populations level off at the same time that we see more and more limits to growth. " 

Source: after Chapman and Reiss 1995


Humans, like any other species that conquers a new habitat, shows an exponential population growth. What is unique for us is that we have been able to radically expand our ability to tame nature and other organisms and direct their production to our stomachs and our bodies. Instead of following a typical S-curve of growth, we have two times restarted population growth. The first time was with the introduction of agriculture, the so called Neolithic or agrarian revolution. Before that, our population grew mainly through expansion into larger and larger areas and into more and more ecological niches. Our role was more or less the same, we lived on the surpluses from other species, which we collected, hunted or fished depending on niche. Population growth was very low, perhaps just 0.001 percent per year (to be compared with 1.8 percent 1990). 12,000 years ago, we were probably less than ten million on the planet, and most likely, the ecological limits for further growth were reached. With the transition to agriculture, many more could be fed from a defined area, but not everywhere, as some parts of the world are not suitable for farming. A period of rapid growth ensued. In ten thousand years, the population grew 250 times. At the time of the industrial revolution, the population had reached the new ecological limits in many places in the world. Not so densely exploited areas were rapidly filling up with settlers from Europe, representing one third of the annual population growth of Europe. Through the deployment of huge amounts of fossil fuel, first coal followed by oil, we got the possibility to, once again, take a giant leap to new levels (Chapman and Reiss 1995, Livi-Bacci 1992).

Improvement in technology, could in each kind of society lead to some possibilities for expansion, e.g. spears and digging tools could allow hunter and gatherers to harvest a larger share of the surplus of their habitat; the introduction of crop rotations and other improved agriculture method could perhaps double or triple the yields, but it was only through employment of industrial technology that yields could increase tenfold. In the same way, improvements in technology has constantly expanded our ability to feed more and more people on the planet also during this industrial phase, but limits are now occurring from all sides. It is hard to see what could be a similar radical change of conditions which would allow us the make another giant leap in population. The options seem to be expansion to new planets; or the introduction of a totally managed planet, with abundant energy sources (e.g. solar or nuclear) and the production of synthetic food on a large scale. Failing any of those, we have to make the best out of what we know and have. Part of that is keeping the population on reasonable levels.

Too few is also not always good

While we can agree than the size of the population is a problem, there are many examples of how high population density forces a more sustainable use of the landscape than a sparse population. e.g. In Germany, Japan and Sweden it was first the exhaustion of, or the threat of exhaustion of, forest resources that compelled people to manage the forests properly and it was the increasing population that made farmers abandon the extractive practice of sod cutting to fertilise their soil (Radkau 2008). Similarly, regardless of how much environmentalists and foresters condemn swiddening agriculture, it will continue to be the norm until population density reaches a certain level, simply because it is the most comfortable, and secure, and also sustainable, way of getting a good return on  labour input. It is pointless to try to make poor farmers switch to other cultivation system before the productivity of the agro-ecosystems is threatened. Already the Egyptians, who operated a limited, but fertile land resource knew that it was beneficial to alternate cereals and fodder crops such as clover or alfa alfa (Mazoyer and Roudart 2006), but it was only under the pressure of population that crop rotations that integrated fodder production and grains became wide-spread in Europe. Similarly, it is the population density of China over a long period that made the Chinese utilise human excreta in an efficient way, while in sparsely populated Africa it was not in use. So while a big population in general is problematic, there are situation where it is not that bad, or at least where we have not managed well with low population.
Some of the ecosystems we have created are dependent on humans, and that with continued urbanization, we actually get more and more areas that are depopulated. Because we have not planned how these depopulated landscapes shall look like and work, societies end up paying farmer or entrepreneurs to ”maintain” the landscapes or preserve the ”cultural heritage”. And it is not only in high income countries this is a problem. Some areas with traditional rice paddies experience labour shortages to maintain the infrastructure. In 2007, I visited traditional farms in Bali and their main problem was that youth preferred to work in the tourism industry over farming. In that way the truly amazing landscape and culture was no longer sustainable as people voted with their feet for another life. If the terraces are not maintained, they will collapse from erosion, with potential devastating landslides as side effect.

Numbers are stabilizing

Forty-three countries, including Japan, Russia, Germany and Italy have populations that are stagnant or even decreasing. A larger group of countries, including China and the USA, has reached the stage where new families will be smaller. When next generation reaches fertile age, population will stabilize. The third group will have doubled its population from now to 2050. This group includes many of the African countries, such as Ethiopia, Congo and Uganda. The predictions of the UN have three alternatives for 2050, 10.8 billion, 9.2 billion or just below 8 billion. Most seem to bet on the middle alternative. That Malthus’ horror scenario of mass starvation has kept its appeal over two hundred years coincides with the start of the demographic transition of England following an unprecedented population explosion. And that pattern has been repeated in country after country, so in the same way as Ireland was the frightening example hundred-fifty years ago, Nigeria or Ethiopia are now. Studies of the demographic transition in the high income countries show a strikingly similar pattern in most countries. First death rates decline rapidly - and it is not primarily the old that live longer but more children that survive. This leads to very big cohorts of youth, reaching 35 percent to 40 percent of the population. When birth rates go down after a while, a big wave of people will reach the stages of young adults, mature adults and old people.

Why is population stabilizing?

It is perhaps a strange question, but it is much more remarkable that the demographic transition has taken place and that populations are not growing, than that there has been a population explosion. After all, we have been taught that the strongest driver of them all is to reproduce, to spread our genes. And why are populations stabilizing now and not hundred years earlier or hundred years later? Why is it not stabilizing in the countries where population is still growing? Is the reason technical, such as contraceptives; economic, such as increased wealth; human, such as improved education of women or is it social, perhaps a result of shift in values? It is interesting to understand what drivers which make individuals change their reproduction. There are actually very few reasons for why a European woman (or her possible partner) today only wants two children, while she wanted four some hundred years ago. It appears to completely contradict the socio-biological ideas that humans only act with the purpose to spread her genes. If that were the case, voluntary birth control would never occur. It is more a process of culture and values. For a long period, it was well known that smoking causes cancer and other diseases. Still it was a long and slow process until this insight led to a changed view on smoking and subsequent regulations. It is interesting that the view on smoking is now changing in all countries, also in countries where smoking is perhaps not a primary health problem (because people don’t live long enough to die from cancer). In the same way it appears that the regulation of populations have little to do with if the country is overpopulated or not. Sweden and the Netherlands stabilized their population more or less at the same time despite that the actual population density is very different, large tracts of Sweden are rather "underpopulated" if there is such a thing. So called soft factors, values and education, seem to play a big role here. At the same time, on a global level, it is hardly a coincidence that populations level off at the same time that we see more and more limits to growth. 

Extract from Garden Earth


  1. I think it may be wise to reflect a little on what the use of log-log scale implies. If population growth is exponential then a growth curve (time * log population) will be a straight line. Historically, however, the population growth rate has been increasing over time; "Population growth was very low, perhaps just 0.001 percent per year (to be compared with 1.8 percent 1990)". In a (time* log population) figure this would show up as a curve that gets steeper over time. This can, as I see it, be a reason for using a log-log curve as Chapman and Rees do. But in a log-log diagram it is no longer the case that a decreasing slope implies an decline in the exponential growth rate. Here, instead, a decreasing slope implies that the increase in the growth rate is a bit slower.

    My guess is that the average reader can have difficulties in interpreting the log-log diagram correctly. It gives the impression of a (Malthusian) process where population growth is slowed down by resource scarcities, where in fact the remarkable truth about human populations is that increases in population size have increased the population growth rate. This point is also hinted at in the discussion of the s-curve but the diagram does not really help in making this clear.

  2. Bo, it is probably true that the interpretation and understanding of the log-log scale is challenging. A point in my discussion is that we by redesigning our ecological niche have been able to "get around" the Malthusian process (I haven't read Malthus so I have only the popular understanding of what that means). I don't think starvation was the main regulator of population growth in the hunter and gatherer society or in the agrarian societies as such. I believe most society developed other ways of regulating population growth compared to available resources by a combination of social/cultural and biological/physical measures. So even if starvation wasn't the mechanism, I believe societies in one way or the other managed to regulate its population (those that didn't probably just expired.

    I believe the unleashing of (fossil) energy linked to industrialization is a key factor to understand why population growth increased so much in the last two hundred year. The wave of growth follows fairly well the wave of industrialization. It is hard to discern cause and effect though. But many factors that we often hear, like better hygiene, and increased survival of children, introduction of markets are quite linked to the use of energy. I don't think that it was scarcity in a direct and brutal way that limited populations historically and it is certainly not that now either. The demographic transition ends with societies with little growth, little desire to have many children and ultimately stagnating energy use. I believe our modern societies have reached limits for growth in a physical and biological sense (while we can go on selling services to each other) in the same way as the agrarian society had largely done that 200 years ago. We have to remember that it was cheap energy that made it possible to increase productivity in farming, both productivity per labour hour and per hectare and thereby also enabled rural exodus as well as smaller families. I don't promote "energy" as the sole factor to explain everything and I believe that it is very difficult, and probably futile to try to define THE factors that changed everything, both historically and today. I don't think that it is awareness of Peak Oil that makes young couples have only two ore fewer children, but somewhere I believe there is a connection in this process of "maturing".