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 Impact = People x Affluence x Technology


william schlesinger
President Emeritus, Biogeochemist

On several occasions, I’ve used this column to espouse the benefits of a lower rate of human population growth. Invariably I hear that I have missed the point; many claim that environmental impacts are driven by the high consumption patterns of modern society and not by the number of people.

My argument is that both people and consumption are central, as John Holdren and Paul Ehrlich pointed out years ago, with their equation: Impact = People x Affluence X Technology (IPAT).

Thomas Malthus (1766-1834) postulated that it is inevitable that greater food production will lead to more population growth that restores the original per capita availability of food, rather than a higher standard of living. His argument has been used for decades in various efforts to curb human population growth, culminating in the Zero Population Growth movement in the late 1960s. Lately it has fallen out of favor, particularly by those who argue that having more people on the planet has not decreased the well being of those alive today. Agriculturalists have responded to the challenge of more people with better crop varieties, irrigation waters, fertilizers, pesticides, and soon potentially with enhancements to the photosynthetic mechanism itself. More people are assumed to stimulate economic growth and the provision of more goods and services. Sadly, the bounty of more people is not always distributed evenly among them.

Having just finished Derek Hoff’s book, The State and the Stork, I am struck by two fundamental deficiencies in the anti-Malthusian view. First, it is anthropocentric, looking only at the health and wealth of humans apart from the rest of nature. Second, it focuses on the provision of goods and services to humans, without regard to the generation of wastes and toxins delivered by humans to the environment. For the latter, we need look no further than the carbon dioxide emitted from fossil fuel combustion and its likely disruption of the basic biophysical conditions of the planet that we have enjoyed throughout human history. Human population growth and CO2 concentrations in the atmosphere have a near perfect correlation.

As I look at the land cleared for new housing in central North Carolina, I see Malthusian impact not played out on the human population, but on nature. Nature is crisscrossed by roads, inflicted with noise, and dramatically illuminated at night. These stem, not from greater consumption, but simply from the provision of more living space for more human beings at the expense of nature. When we leave less natural habitat for the other species that share the planet with us, we suffer a loss of our natural heritage and from a loss of open spaces to reflect and unwind. Even those are human-centric views. When we are more circumspect, we will see that the habitat we have usurped is the only and rapidly diminishing home for the species that we drive away—they have no choice.

We must look beyond the self-centered view that we are the only masters of our own survival. Numerous field experiments over the past several decades show that in experimental plots with diminished species diversity, plant productivity and resilience to external perturbations are lower.

When birds are excluded from forests, insect damage rises and forest health declines. When populations of native animals are lower, human health risks to Lyme disease and other tick-borne illness increase. We will not engineer ourselves to a cornucopia of food, without maintenance of the species that help agricultural systems avoid periodic drought, insect attack, and invasion of weeds.

Applications of neonicotinoid and other pesticides give the false impression that we may increase the yield of crop plants, but not if we simultaneously diminish the abundance of pollinating insects and increase the burden of pesticides in our own bodies. Maintenance of the full diversity of nature means maintenance of a full diversity of habitat, unspoiled by human activities.

Clean water, clean air and diverse forests are not just for us, but also for the species that maintain planet Earth, the only place where we know life.

Population matters: the child not born leaves no footprint on nature.


Buxton, R.T. and 6 others. 2017. Noise pollution is pervasive in U.S. protected areas. Science 356: 531-533.

Gaston, R.J. et al. 2013. The ecological impacts of night-time light pollution. A mechanistic appraisal. Biological Reviews 88: 912-927.

Hoff, D. 2012. The State and the Stork. Uniiversity of Chicago Press.

Holdren, J.P, and P. Ehrlich. 1974. Human population and the global environment. American Scientist 62: 282-292.

Keesing, F., et al. 2010. Impacts of biodiversity on the emergence and transmission of infectious diseases. Nature 468: 647-652.

Mantyla, E., T. Klemola and T. Laaksonen. 2011. Birds help plants: a meta-analysis of top-down trophic cascades caused by avian predators. Oeccologia 165: 143-151.

Ritters, K.H. and J.D. Wickham. 2003. How far to the nearest road? Frontiers in Ecology and Environment 1: 125-129.

Schramski, J.R., D.K. Gattie, and J.H. Brown. 2015. Human domination of the biosphere: Rapid discharge of the earth-space battery foretells the future of humankind. Proceedings of the National Academy of Science 112: 9511-9517.


william schlesinger
President Emeritus, Biogeochemist

William Schlesinger is active in communicating science to policy makers and media. He has testified about environmental issues in Congress and in state houses, and has been featured in media including NOVA, the Weather Channel, Discover, National Geographic, and the New York Times.

He discusses a range of environmental issues in his weekly blog, Translational Ecology.