Population dynamics: a century of growth, a future of decline Premium

Explore the history, challenges, and future of global population trends, from overpopulation fears to the emerging concern of depopulation.

Throughout the 3,00,000 years of human existence on earth, demographers estimate that approximately 108 billion people have lived so far. Remarkably, until 1804, the global population never exceeded 1 billion at any given time. However, this began to change with the advent of industrialisation and improved living conditions.

Today, at 8.2 billion (that’s 7% of the population that has ever lived on earth), the world’s population is at its highest point in history. Projections suggest that it will continue to rise, reaching a peak of around 10 billion by 2080. Yet, despite this upward trend, the emerging global concern is not overpopulation but rather the long-term implications of population decline.

For centuries, fears of overpopulation have shaped public policies. This narrative has shifted in recent years, with concerns about depopulation. As the world’s population is at its peak, this change in focus may appear paradoxical. This paradox underscores the need to reassess our understanding of demographic shifts and their consequences.

The debate over population growth began in the late 18th century when Thomas Malthus theorised that unchecked population growth would outpace food production, leading to famine and societal collapse. His predictions were echoed by scholars until the 20th century, including in Paul Ehrlich’s The Population Bomb, which warned of catastrophic consequences of overpopulation. Advances in public health, nutrition, sanitation, antibiotics, and the availability of birth control pills defied these doomsday predictions, fuelling population growth. Now, the conversation has shifted to the challenges posed by population decline for the first time in modern history.

Population depends on birth, death, fertility, and migration. Globally, net migration is zero unless we colonise Mars, leaving fertility and mortality as the main drivers. Total Fertility Rate (TFR) and Net Reproductive Rate (NRR) are key indicators that help predict future trends. TFR measures the number of children an average woman bears, and NRR measures the number of daughters an average woman bears in her lifetime.

A TFR of 2.1 is considered the replacement level, meaning each woman and a single living partner produce two children to replace themselves. The extra 0.1 accounts for infant mortality, stillbirths, neonatal deaths, and abortions. This TFR must align with an NRR of 1.0 for population stability, signifying each woman produces one daughter. A TFR of 2.1 and NRR of 1 ensure the population replaces itself across generations. The global TFR has dropped to 2.4 from 5 in the 1960s, signalling a potential long-term decline. However, regional variations complicate this picture. While South Korea reports a TFR of less than 1, and Uganda reports a TFR of more than 5, developed regions like Europe, East Asia, and parts of India have replacement levels with TFRs of 1.6-1.9.

A population age pyramid (see pic) is a visual and graphical representation of a population’s age and sex distribution. It provides insights into the demographic structure, indirectly reflecting birth and death rates. Its shape helps predict future trends, enabling policymakers to plan for resources like healthcare, education, and workforce development.