Revised 23 August 2021

This section provides a non-mathematical primer on the principles of population dynamics and a background on the prospects of the world population achieving Zero Population Growth (ZPG). For a comprehensive description and the mathematics of population dynamics, I recommend the book Applied Mathematical Demography by Keyfitz & Caswell, 2005. 

Population dynamics is the study of changes in population size by tracking births, deaths, and net migration. The size of the world population in 10,000 BC is estimated to have been 2.4 million people (Hyde, 2019). As shown in Figure 1, growth in the size of our human population was very slow for many thousands of years. It is only over recent centuries that growth has accelerated.

Figure 1: History of World Population Growth (Data: Hyde, 2019)

The number of years that it takes for an exponentially growing population to double in size, or doubling time, is approximately 70 divided by the annual growth rate as a percentage. For example, a population growing by 2.0% each year would take 35 years to double in size. Table 1 below shows it has taken almost 12,000 years and 11 doublings in size for our human population to grow from 2.4 million people in 10,000 BC to 5.0 billion people in 1986. If our human population of 12,000 years ago had doubled in size at a constant annual growth rate of 2.0% per year, a rate that was surpassed in the 1960s, then it would have taken 385 years (35 years x 11 doublings) for the world population to increase to 5 billion people. 

Table 1: Historical Human Population Doubling Times (Data: Hyde 2019)




Doubling Time (Years)

Average Annual Growth Rate


10000 BC


8148 BC




6387 BC




4821 BC




3305 BC




1834 BC




432 BC




1033 AD




1706 AD




1847 AD




1949 AD




1986 AD




As shown in Table 1, the average annual growth rate of our human population between 10,000 BC to 1000 AD was very slow at 0.04% per year. The average annual growth rate increased significantly between 1000 AD to 1700 AD (0.11% per year) and then started to progressively accelerate from 1700 to 1850 during the start of the industrial revolution (0.50% per year), from 1850 to 1950 during large scale mining of coal and drilling of oil (0.69% per year), and then especially from the 1950s through to the 1960s during the green agricultural revolution (1.89% per year). 

During the 20th century our world population doubled within one lifetime and there are now strong signals that our world population has exceeded the carrying capacity of our planet Earth (Cohen, 1995). The per capita rate of consumption and the impact of using resources can be reduced more so than that which is current by increasing the efficiency of using resources and by greater use of recycling. However, there are physical and thermodynamic limits to the possible extent of increases in efficiency and recycling which are addressed in Section: Green Growth. Both efficiency of use and recycling are subject to diminishing returns. 

Regardless of the per capita rate of consumption of resources, a larger human population will consume more resources than a smaller population. Continued growth in human populations exacerbates the impact of climate change and accelerates the peaking of fossil fuels (Section: Peak Energy) and mining of minerals (Section: Peak Minerals) at the very same time that fossil fuels are needed to enable a transition to renewable energy. Continued increases in population during a transition from fossil fuels to renewable energy can but only result in a Sisyphus like undermining of efforts for a smooth transition. 

In 1972 the Club of Rome published the book The Limits to Growth which advocated ZPG as soon as possible (Meadows et al., 1972)). The world population back then was 3.8 billion people. By January 2019 the world population had grown to 7.7 billion people (United Nations, 2019) and the world population continues to grow, continues to consume more fossil fuels, and continues to add more CO2 and methane to the atmosphere. Partial good news is that the annual growth rate of the world population peaked at 2.11% in 1971 and since 1971 the world population has continued to increase in size, but at a declining growth rate.