The Limits to Growth, Meadows et al (1972), used the systematic model technique promoted by Jay Forrester at MIT. “All models are wrong. Some are useful.”

Reading the book started me looking at demographic trends. In 2010, I developed a very simple model for world population growth. The peak population occurs in 2047 at 8.54 billion, which is only 11 percent more than the current population.

Each year, I compare the model results to the actual numbers published by the CIA in The World Factbook. In 2021, the CIA reports a world population of 7.772 billion and a growth rate of 1.03 percent. The numbers from the model are 7.708 billion and 0.80 percent. Because the differences are small, I will not change the model.

I also calculate the impact of the 10 largest countries. (Note that I retain Japan as the 10th largest country even though Mexico now has a larger population. Including Mexico in the top ten in place of Japan would introduce “drift” such as that encountered by the Dow 30 and Fortune 500.)

The 10 largest countries have 57 % of the world’s population. The combined fertility rate of these countries has declined from 2.17 in 2014 to 2.09 in 2021. The current rate of fertility is about the level needed for replacement. Two of the countries, Russia and Japan, have declining annual growth rates of -0.20 % and -0.37% respectively. Of the ten largest countries, only India, Pakistan, and Nigeria have fertility rates above the replacement level. The fertility rates in all ten large countries either continue to fall or remain below replacement levels.

Examining the age and gender cohorts of the populations reveals some interesting facts. The 25 to 54 age brackets of males plus females are 652 million in China compared to 551 million in India. The 15 to 24 age bracket of females are 74 million in China compared to 108 million in India. Given the respective fertility rates of 1.6 and 2.23, the annual birth rate in India will soon be twice that in China. Within ten years, the 25 to 54 age cohort in India will exceed that of China. Soon thereafter, India will be larger and the difference will be material. This change in relative levels will impact geo-political calculations and perhaps investment decisions.

In other notes, I have pointed out that peak farmland is in the past. Improved agriculture practices (productivity is much greater than population growth) will continue to improve diets. Technology advances in manufactured foods (Quorn, Heme) will compete with protein from animal husbandry and perhaps with protein from agriculture. Urban farming will reduce the need for farmland. In ten to fifteen years, electric vehicles will reduce materially the need for corn to ethanol in the United States. Marginal farmland in remote areas may not be a good investment.

The models used in The Limits to Growth were based on continuous exponential growth. The rates assumed in the models have changed. Therefore, many of the conclusions in the book are no longer valid.


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