I can think of no subject related to the environment that garners more heated debate than the suggestion that we should curb human population growth. It gives immediate rise to accusations of racism and elitism. For many, it flies in the face of God’s Biblical orders to be fruitful and multiply. For others, it repudiates the basic tenet of Darwinian evolution that the fitness of organisms is based on the number of offspring left behind. And many simply don’t want to discuss a subject that is so personal and private as human reproduction.

Those who reject the importance of population as an environmental issue stress that resource consumption rather than population size has led to our current global environmental impact. True, resource consumption is central, leading to perhaps two thirds of the growth in carbon dioxide emissions in recent decades. But, resource use begins with the first diaper slapped on a new born infant and ends with the last blast of natural gas for a cremation. The child not born uses no resources.

Decades ago, John Holdren and Paul Ehrlich codified the human environmental impact in the multiplicative equation I = P x A x T, where P is population size, A is affluence and T is technology. They recognized that technology might sometimes reduce or modify impact, as when the discovery of illuminating oils led to a shift away from hunting whales. But, the positive confounding of population multiplied by affluence (as a measure of resource use) renders moot the “one-or-the-other” argument about the causes of environmental impact, that generates so much more heat than light in current debate.

No one will advance with the argument that we should embrace a lower standard of living for any person living on any continent. To improve efficiency at lower cost, we may substitute solar power for coal, electric- instead of gasoline-powered vehicles, and LEDs for incandescent lights. But, we will not replace the basic need for space for human occupancy and food for them to eat.

There is a finite amount of land available, fertile soil, and photons that fall on it, which will determine the habitat and food supply for humans at the expense of the rest of the Earth’s biodiversity. Somehow many of us find it easy to overlook the role of growing human population in the loss of a local woodlot in favor of suburban development and for the increasing demand for food that destroys Amazonian rainforests.

There are now 7.8 billion humans on planet Earth, each in pursuit of the good life. Economists love population growth that factors into traditional measures of economic growth. With each increment of GDP, our rising numbers extract more materials from the Earth’s crust and cast more effluents into its atmosphere and oceans.

We can hope that innovation may further lower resource use per capita, but It is not as if the new additions to our population will not consume resources. And, with more of us, the impact on the environment will grow. Talk of sustainability is hollow when the human population on the planet is growing at 1% each year—doubling every 67 years. Only with a population growth rate of zero might we have some hope for planetary stability.

12 thoughts on “Overpopulation

  1. Thanks Bill for your direct and clear message. Years ago my wife and I chose to have a child free family. We enjoy our nieces and nephews and the children of our friends and treat them with love and tolerance when necessary. But we’ve rarely felt compelled to join that parenting crowd. In case this message sounds cold I want to assure readers that we are good people and have committed our lives to helping people and supporting communities where we’ve lived. Traditionally, people made children to help them hunt, to work on the farm and to hopefully care for them in their old age. We’ve done OK without support in the first two categories and hope life will be gentle during the last one. We are very aware of the resources and sustainability focus of your message. Every now and then I meet a couple who are planning with those thoughts in mind. More power to them and may their numbers grow!

  2. Bill, The one factor you are leaving out is the recent dramatic drop in family size in ‘rich’ or ‘developed’ societies. Europe, Japan, South Korea, China, and North America are all already in negative population growth territory, when immigration is subtracted. One can argue about the reasons for this, but very high childhood survival rates, social safety nets for older people, and the high cost of raising and educating children (especially when both parents need to work) are good starting points. Population growth is arguably becoming limited to poorer societies that lack the above and basic female literacy and birth control. Admittedly, bringing the rest of the world up to ‘Western’ economic standards can have negative ecological impacts, but that appears to be the ‘natural’ solution to population growth. Whether we reduce birth rates by reducing poverty or not, we still need to reduce the environmental cost of a unit of GDP, for instance, by vastly expanding alternative energy sources to displace fossil fuels, improving energy efficiency to reduce requirements, and moving to synthetic meats (vegetable or cultured animal proteins) to eliminate some 60% of agricultural land requirements.

    1. There are some indications that the expected reduction in fertility are reversed at high levels of affluence. See Myrskyla, M., H.-P. Kohler, and F.C. Billari. Advances in development reverse fertility declines
      Nature volume 460, pages741–743(2009)

      Also, as treated in one of my earlier blogs, achieving a rate of zero population growth would require nearly 6X the energy use as we see today. See: https://blogs.nicholas.duke.edu/citizenscientist/a-modest-proposal/

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