Last updated July 4, 2025

World Population: From One Billion Humans to Demographic Saturation

Evolution of the world population between 1800 and 2100

An exponential leap since the industrial revolution

In 1800, the world's human population was estimated at about 900 million inhabitants. Two centuries later, in 2020, it exceeded 7.8 billion. This dizzying growth is the result of an exponential dynamic fueled by medical, agricultural, and technological progress. This growth is modeled by the equation: \[ N(t) = N_0 \cdot e^{r t} \] where \( N(t) \) is the population at time \( t \), \( N_0 \) is the initial population, and \( r \) is the average growth rate. Until the beginning of the 21st century, the parameter \( r \) reached values close to \( 0.02 \), or a growth of 2% per year. This evolution is explained by a strong reduction in mortality without an initial decrease in birth rates—a characteristic desynchronization of phase 2 of the demographic transition.

Towards global saturation?

United Nations projections indicate that the world population could reach a peak of about 10.4 billion individuals by 2080, before stabilizing or declining slightly. This leveling off is explained by global demographic convergence: most countries are experiencing or will experience a drop in fertility below the replacement level (\( \sim 2.1 \) children/woman). From this point on, natural growth becomes negative, unless compensated by migratory flows or pro-natalist policies.

This asymptotic dynamic reflects the depletion of resources, water stress, growing inequalities, and negative feedback related to climate change.

A future polarized between Africa and global aging

From a spatial point of view, 21st-century population growth is highly polarized. Nearly 80% of the increase by 2100 will be concentrated in Sub-Saharan Africa. In contrast, many regions (Europe, East Asia) will experience a decline. This heterogeneity creates strong geopolitical, economic, and migratory tensions.

Furthermore, the global demographic transition is accompanied by rapid aging: the proportion of people over 65 could reach 25% by 2100, profoundly modifying economic balances and social models. This corresponds to a transition of the demographic system towards a new dynamic attractor, where biological entropy increases to the detriment of global reproductive potential.

Estimated World Population and Annual Growth by Continent (2025)

Continent	Estimated Population (2025)	Share of World Population	Annual Growth (%/year)
Asia	4,790,000,000	59.3%	+0.6%
Africa	1,490,000,000	18.4%	+2.4%
Europe	740,000,000	9.2%	−0.1%
Latin America and the Caribbean	670,000,000	8.3%	+0.6%
North America	380,000,000	4.7%	+0.4%
Oceania	46,000,000	0.6%	+1.2%
World Total	8,120,000,000	100%	+0.9%

N.B.: The figures are deliberately rounded to the nearest million.

Estimated World Population in Real Time

Dynamics of a Global Living System

World population growth from 1800 to 2100 illustrates the behavior of an open living system: a phase of rapid growth under external energy and technological input, followed by saturation and bifurcation towards a new steady state, or even decline. Future balances will depend on many coupled parameters: education, public policies, climate, reproductive technologies, and inequalities.