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Population and a Dose of Common Sense

by Blake Alcott

It isn’t true that population size (relative to the size of the earth and its resources) is the “main cause” of unsustainable environmental impact, or the “main problem” when it comes to depletion, pollution, and other concerns over health and happiness for people today and in the future. It also isn’t true that “the real problem” is too much consumption per person by rich people. It is both. It is P x A in the formula:

Impact = f(Population, Affluence, Technology), or simply IPAT.

Many researchers have measured the relative contributions of population and affluence to various kinds of impact. However, since decreases in population can be offset by increases in affluence, and vice versa, changes in either factor do not necessarily lower impact.

Can we be complacent about population size? Can we count on declining birth rates to stabilize or even lower population, now over 7 billion and increasing by 80 million per year (the size of Ethiopia’s population)? We are also, after all, experiencing declining death rates, and rising life expectancy counterbalances declining fertility to some extent. The deeper question is whether a population of 7 billion — or 8 billion or even 11 billion (low and high projections) — exceeds the earth’s carrying capacity.

The number of people that can live on earth obviously depends on how much food we can produce now and over the long term. The evidence suggests that we cannot count on food production to keep pace with population growth:

  • Very little land remains to be converted into agricultural hectares;
  • Such land conversion incurs high costs;
  • Yields per hectare can rise significantly only in Africa and South America;
  • Soil degradation and groundwater depletion curtail production;
  • Petroleum scarcity will increasingly constrain food production because agriculture requires fuel for machinery, water-pumping, and transport as well as oil-derived fertilizers and plastics.

A population’s sustainability depends on its affluence. Therefore, before any society can compute its carrying capacity, it must first decide what material lifestyle it wants — how much it wants to consume. Does it want to eat meat (and not just grain), or use land for sports and entertainment (and not just agriculture), and does it want wilderness for other species? If so, its maximum population is proportionally lower. Once a society has politically decided its desired level of affluence, it can assess appropriate technologies for producing its goods and services most efficiently. Only then can a number be calculated for a desirable and sustainable population size.

Population and affluence are both components of overall environmental impact.  Credit:

Many countries, if they were to estimate these parameters, would conclude that they are overpopulated, especially if they remember that sustainable size takes into account the rights of future generations and the desirability (on either utilitarian or ethical grounds) of leaving room and resources for non-humans.

Once overpopulation has been recognized, the search for appropriate population policies begins. In the rich countries (the ecological footprint of a rich child, ceteris paribus, will be greater than that of one born in poverty) one could end subsidies for child-bearing, including tax breaks, salary bonuses, parental leave from work and even one-off payments for having a child. Any policy change must consider the rights of already-born children and the goal of gender equality. In poorer societies there is unmet demand for the means of preventing pregnancy. Birth control “technology,” if available to all who want it, would cut today’s 80 million excess of births over deaths by perhaps two-thirds.

Whether rich or poor, a country could also choose to adopt direct policies. Some possibilities, as promoted by many ecological economists, are:

  • Ending subsidies after a couple’s second child;
  • Offering payments for sterilization;
  • Imposing tax penalties for large families; and
  • Setting quotas for child-bearing.

These measures however raise the question of whether a society has the right to legislate how many children its members can have. On this issue, two questions are often confused: (1) the legitimacy of restrictions on individual procreative freedom itself, and (2) the legitimacy of the political process deciding them. If it is an inalienable right to have as many children as one wants, then quotas and other constraining policies would be out of bounds. Treating procreation in this way fits well with the laissez-faire, individualist philosophy of our time. The opposing view holds that reproductive freedom has limits, that at some population level, the interests of society are harmed, and restrictions that support the common good are acceptable and even desirable. Population size, moreover, is one of many issues affecting living beings without a vote, namely other animals and future humans. Concrete proposals have included the right to one child, with permits being transferable (for free or for a price) to someone else.

Such direct policies can be decided democratically or autocratically, and it is the latter that leads many to think immediately of “compulsion” or “coercion” when imagining them. However, every law, by definition, coerces us, so let us just agree to use a democratic process and reject the option of an authoritarian eco-regime. The question then becomes: is it legitimate for a majority — say, 51 or 60 or 66% of the voters — to restrict everybody’s procreative activity? A majority cannot, after all, legitimately legislate the incarceration or death of all red-heads.  But red-heads don’t pose the same problems that overpopulation does.

There is truth in the statement, attributed to David Attenborough, that one cannot conceive of an ecological problem that wouldn’t be easier to solve with fewer people. For example, in poorer countries, hunger and environmental degradation could immediately be mitigated if there were less demand for resources. The issue is to figure out first how many fewer people we’re aiming for, and second how to make a transition that is democratic, compassionate, and fair.

For more details on this topic, see the full paper, which raises more questions and offers many references for further reading.

Alcott, Blake, 2012, “Population matters in ecological economics,” Ecological Economics 80: 109-120. (accessible at > Publications)


3 Responses to “Population and a Dose of Common Sense”

  1. Tim Gieseke says:

    D. Attenborough’s statement must be assuming that all peoples and cultures consume and pollute at the same rate.

    In that similar vein, we could look at consumptive entities in general. This was recently described to me from a biological perspective of Corporatis profitis and Homo sapiens and the common niche they both occupy. If Hs has the difficult-defined goal of “happiness” and Cp has the laser-focus goal of “profit” and each living entity occupies the same niche, then according to Gause’s Principle of Competitive Exclusion, one entity will be driven out the niche and become extinct or must adapt to a slightly different niche.

    As Corporatis profitis converts natural capital to financial capital, it has a tendency to limit many of the Homo sapiens in meeting their objective. Their objectives are not coupled to meet Homo sapiens goals, although the Supreme Court ruled that Corporatis profitis is also a “person” gving them rights not previously enjoyed.

    The core of the advancement of any being is its ability to transform itself to adapt. With Homo sapiens, we rely on genes that get a re-look every generation. With Corporatis profitis they rely on memes that have the capacity to transform, replication, and reproduce nearly instantaneously.

    The horror films are often associated with the robots that Hs will create one day and take over our niche. But here it is, giant, kind of invisible and with an insatiable appetite – and it wants to live in the niche you are. I think sustainability is easier to achieve with 7 billion Homo sapiens, rather than a few thousand Corporatis profitis with the laser focus of converting, really anything they can get their mandible, into “Profit”.

    I agree, it is not true that population size is the main cause of ecological and the economical degradation.

  2. Nick Palmer says:

    Re: population

    When I was at school there were 3.6 billion people. Dividing that number into the land surface of Earth gave a figure of about 200 meters square per person.

    Now we have 7 billion and our personal share of the surface has reduced to a square 145 meters on a side.

    That is why our current system is not sustainable – in only 50 words…

  3. Sven Persson says:

    From Clive Hamilton’s (2010) ‘Requiem for a Species: Why We Resist the Truth about Climate Change’:

    “Making a number of reasonable assumptions for various countries about fertility rates and future per capita carbon emissions, the researchers estimate that the carbon legacy of the average female in the United States is 18,500 tonnes of CO2 while that of a Bangladeshi woman is only 136 tonnes. In other words, the future stream of carbon emissions following a decision by an American couple to have an extra child is 130 times greater than that of a decision by a Bangladeshi couple. Put another way, to have the same impact on future global carbon emissions, a decision by one American couple not to have a child would have to be matched by 130 Bangladeshi couples. So population policies should be targeted now at the United States and the larger European countries (including Russia) rather than poor but populous nations like Bangladesh, India and Nigeria. The US–Bangladesh comparison is the most extreme case, but even comparing the carbon legacies of parents in the United States and China gives a factor of nearly five. For India the factor is nearly 50. In short, it makes no sense to single out population growth without linking people to their expected consumption.” (p. 43)

    So, who are there too many of? Rich or poor people? Which is a more important human right: the right to your own reproductive organs and their usage, or the right to over-consume?

    “It’s no coincidence that most of those who are obsessed with population growth are post-reproductive wealthy white men: it’s about the only environmental issue for which they can’t be blamed.” (George Monbiot,

    And yes, I understand that population size is a problem.

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