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How Many People Can the Earth Carry? Watch Out for The Rule Of Expert

December 9, 2012

How many people can Earth carry? This is arguably the most important question facing humanity today: it has to do with energy consumption and the quantity of fossil fuels left to be burnt as much as with food production, consumption and distribution. The answer to this question today is premised on two assumptions: firstly, there is the nature on one side and the society and forms of social lives on the other. Secondly, there are experts on one side who knows the nature, can tell how much oil is left and how much food can be produced and can produce evidence which show what policies works best given their technical findings; and there are layperson on the other side who live in a society whose forms are shaped by what experts say. The question about human carrying capacity falls within the realm of nature and one is told to leave the answer to the experts: the layperson, situated within the society, has little saying in it. This post will explain why asking how many people can Earth carry is far from a purely technical question about nature’s capacity, it will apply this thinking to two of the key concepts (i.e. peak oil and peak food production) and will shed light on the dangers of the rule of experts.

Earth’s Human Carrying Capacity. Calculating how many people can Earth support has been a subject in which countless scientists ventured in. Typically the calculation asks how many people, given the present total fertility rate (number of children per woman), one is expected to face by a certain time and looks at what levels of living can the Earth ensure for this number of people. As more scientists were trying to answer this question, one would expect their estimates to increasingly converge around the same value: one was measuring nature after all. In fact it happened just the opposite: with time the scatter among the estimate increased. As Cohen[1] points out, in 1994 estimates published in that year ranged between ❤ billion to 44 billion. Why is then that when one is measuring that objective reality called nature one cannot achieve a consistent estimate? Part of the answer lies in the fact that the earth’s human carrying capacity is dictated by future natural constraints. These constraints are not given exclusively by some external natural process as they emerged out of human choices. When the question of how many people can Earth carry is approached one tend to give more weight on the natural constraints and overlook the role of human choices. One focuses on better understanding nature to see if humanity is really approaching some sort of limit, but does so by putting nature and society in two different compartments. The role of individual and collective choices cannot be overlooked because, as Cohen explains

How many people Earth can support depends in part on how many will wear cotton and how many polyester, on how many will eat meat and how many bean sprouts; on how many will want parks and how many parking lots. These choices will change in time and so will the number of people Earth can support.

Next section will look into two key concepts which are pivotal to answer the Earth’s human carrying capacity question: peak oil and peak food production. It will make a case for why human choices cannot be sidelined and it will argue that understanding nature not as an independent entity but rather as a factor entangled with technical and human elements is paramount for our understanding[2].

The Rule of Experts (source

Peak Oil. Peak oil is a concept which refers to a point in time when the oil extracted is not matched by new discoveries of oil reservoirs: as this happens, oil flow from the underground (and with it consumption) would peak and not increase anymore. When the world will reach this point is the subject of a heated controversy and it is a classical example of how nature is separated by the society. On one side stands the natural constraint i.e. how much oil the Earth has. To estimate petroleum resources one has to take into account a panoply of geophysical and geochemical data: porosity, temperature and water saturation of the source rock which gives an idea of the proportion of the oil in the rock formation which is likely to be recovered. It is not however just about how much oil Earth has; it is also about how much oil can be feasibly extracted. The technical feasibility of projects of extraction is in turn a function of future costs and levels of demand. Estimates of petroleum reservoirs are therefore not only a function of petrochemical and geological factors (how much oil is the lithosphere) but also of economic and political factors. For instance, an estimate of the increasingly inaccessible geological formation in which oil is found depends on a further estimate that equipment which can discover and extract this inaccessible oil will be devised. This in turn is based on the estimates of future prices of oil.

When cast in this light, the division between the geological factor (the nature) and the human factor (the society) blurs: what is below ground (the oil supply stored in the lithosphere) is entangled with what is above ground (the choices of human societies of how much oil is enough). The point is not to assert the primacy of the society over the nature: the direction of causality runs both from above to below and vice versa. It is true that the future cost of extraction will depend for example on the effectiveness of environmental groups to impose a cost on the release of underground store of energy (i.e. oil) into the atmosphere. At the same time however it is also true that geological estimates of reserves determines the feasibility of the extraction of which reserves: when oil companies report the availability of plentiful of resources they create a premium in investing in machinery of discovery and disincentives the switch to other sources of energy.

Next post will look at another pivotal concept (peak food production) and will unpack the dangers of the rule of experts.

[1] Population Growth and Earth’s Human Carrying Capacity, Joel Cohen, Science, 1995

[2] This discussion draws on the argument laid out by Timothy Mitchell in the book Carbon Democracy, chapter 9 No More Counting on Oil

2 Comments leave one →
  1. whocares permalink
    July 28, 2013 4:14 pm

    My brain got confused after the first paragraph


  1. Peak Food Production and the Rule of Experts « Do No Harm

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