"The power of population is so superior to the power of the Earth to produce subsistence for man, that premature death must in some shape or other visit the human race."
The late-18th century philosopher Thomas Malthus wrote these ominous words in an essay on what he saw as the dire future of humanity. Humans' unquenchable urge to reproduce, Malthus argued, would ultimately lead us to overpopulate the planet, eat up all its resources and die in a mass famine.
But what is the maximum "power of the Earth to produce subsistence," and when will our numbers push the planet to its limit? More importantly, was Malthus' vision of the future correct?
Earth's capacity
Many scientists think Earth has a maximum carrying capacity of 9 billion to 10 billion people. [ How Do You Count 7 Billion People?]
One such scientist, the eminent Harvard University sociobiologist Edward O. Wilson, bases his estimate on calculations of the Earth's available resources. As Wilson pointed out in his book "The Future of Life" (Knopf, 2002), "The constraints of the biosphere are fixed."
Aside from the limited availability of freshwater, there are indeed constraints on the amount of food that Earth can produce, just as Malthus argued more than 200 years ago. Even in the case of maximum efficiency, in which all the grains grown are dedicated to feeding humans (instead of livestock, which is an inefficient way to convert plant energy into food energy), there's still a limit to how far the available quantities can stretch. "If everyone agreed to become vegetarian, leaving little or nothing for livestock, the present 1.4 billion hectares of arable land (3.5 billion acres) would support about 10 billion people," Wilson wrote.
The 3.5 billion acres would produce approximately 2 billion tons of grains annually, he explained. That's enough to feed 10 billion vegetarians, but would only feed 2.5 billion U.S. omnivores, because so much vegetation is dedicated to livestock and poultry in the United States.
So 10 billion people is the uppermost population limit where food is concerned. Because it's extremely unlikely that everyone will agree to stop eating meat, Wilson thinks the maximum carrying capacity of the Earth based on food resources will most likely fall short of 10 billion. [ When Will Earth Run Out of Food? ]
According to population biologist Joel Cohen of Columbia University, other environmental factors that limit the Earth's carrying capacity are the nitrogen cycle, available quantities of phosphorus, and atmospheric carbon concentrations, but there is a great amount of uncertainty in the impact of all of these factors. "In truth, no one knows when or at what level peak population will be reached," Cohen told Life's Little Mysteries.
Slowing growth
Fortunately, we may be spared from entering the end-times phase of overpopulation and starvation envisioned by Malthus. According to the United Nations Population Division, the human population will hit 7 billion on or around Oct. 31, and, if its projections are correct, we're en route to a population of 9 billion by 2050, and 10 billion by 2100. However, somewhere on the road between those milestones, scientists think we'll make a U-turn.
UN estimates of global population trends show that families are getting smaller. "Empirical data from 230 countries since 1950 shows that the great majority have fertility declines," said Gerhard Heilig, chief of population estimates and projections section at the UN.
Globally, the fertility rate is falling to the "replacement level" — 2.1 children per woman, the rate at which children replace their parents (and make up for those who die young). If the global fertility rate does indeed reach replacement level by the end of the century, then the human population will stabilize between 9 billion and 10 billion. As far as Earth's capacity is concerned, we'll have gone about as far as we can go, but no farther.
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Natalie Wolchover
As an expert in environmental science and population dynamics, it's evident that the concerns raised by the late-18th century philosopher Thomas Malthus remain relevant to this day. Malthus foresaw a future where human population growth would outstrip the Earth's capacity to provide sustenance, leading to widespread famine and premature death. The quote you provided encapsulates Malthus' apprehensions about the unchecked growth of the human population.
Contemporary scientific assessments, such as those made by renowned Harvard University sociobiologist Edward O. Wilson, align with Malthus' fundamental premise. Wilson estimates Earth's maximum carrying capacity to be in the range of 9 billion to 10 billion people. This estimation is based on a careful consideration of available resources within the biosphere.
Wilson highlights the finite nature of freshwater and the constraints on food production, echoing Malthus' arguments from more than two centuries ago. Even under the hypothetical scenario of maximum efficiency, where all arable land is dedicated to feeding humans, there is a limit to the Earth's ability to sustain a growing population. Wilson's analysis suggests that if everyone adopted a vegetarian diet, the Earth could potentially support around 10 billion people, but the reality is that various factors, including dietary preferences and the allocation of resources to livestock, significantly impact this limit.
Population biologist Joel Cohen of Columbia University expands on the environmental factors influencing carrying capacity, including the nitrogen cycle, phosphorus availability, and atmospheric carbon concentrations. However, he acknowledges the considerable uncertainty in predicting the impact of these factors on the planet's capacity to support human life.
The article also touches on the encouraging trend of declining fertility rates globally. The United Nations Population Division suggests that the world is heading towards a population of 9 billion by 2050 and 10 billion by 2100. However, there is optimism in the observation that fertility rates are decreasing, bringing many countries closer to the replacement level of 2.1 children per woman. If this trend continues, it could lead to a stabilization of the human population between 9 billion and 10 billion by the end of the century.
In conclusion, the dialogue presented in the article reflects the ongoing discourse around the Earth's carrying capacity and the potential implications of unchecked population growth. The perspectives of experts like Edward O. Wilson and Joel Cohen contribute valuable insights into the complex interplay of factors influencing the planet's ability to provide sustenance for a growing population.
