Population momentum describes the continued growth of a population even after fertility rates have fallen to or below replacement levels. This occurs because a large proportion of the population is young, ensuring continued births for several decades.
The Demographic Drivers
Population momentum primarily arises from a youthful age structure. When a large percentage of people are young, they will eventually enter their reproductive years. Even if couples have fewer children, the sheer number of people reaching childbearing age results in many births, driving continued growth. These large young cohorts originate from past periods of high fertility rates. Additionally, improvements in healthcare and reductions in mortality rates ensure more individuals survive to reproductive age, contributing to this demographic inertia.
Illustrative Examples
China, for instance, experienced continued population growth for many years after the implementation of its One-Child Policy in 1979. This was because the large cohorts born during earlier periods of high fertility were still entering their reproductive ages, ensuring a substantial number of births despite the policy’s restrictions on family size.
India is currently experiencing significant population momentum. Despite its average fertility rate having decreased considerably in recent decades, its population continues to grow by over 10 million people annually. This ongoing growth is directly linked to the country’s large young population, a legacy of past higher birth rates.
Malaysia also demonstrates this effect; even though it reached replacement-level fertility around 2000, its population is projected to grow until 2070 because a quarter of its population was under 15 years old.
Societal and Economic Implications
The continued population growth driven by momentum places considerable pressure on natural resources. Increased demand for essential resources like water, food, and energy can lead to scarcity and environmental degradation. This growth also contributes to increased carbon footprints, greater waste generation, and habitat loss, affecting biodiversity.
Sustained population expansion also creates substantial demands on infrastructure. Countries experiencing momentum often face the challenge of providing adequate housing, schools, healthcare facilities, and transportation networks for their growing populations. Meeting these needs requires significant investment and strategic planning.
Economically, population momentum can present both opportunities and challenges. A larger working-age population can potentially lead to a “demographic dividend,” boosting economic output. However, this growth also necessitates robust job creation to absorb the expanding workforce, otherwise, it can lead to unemployment and strain on social security and pension systems.
Pathways to Demographic Transition
Population momentum is not a perpetual phenomenon; it eventually subsides as populations undergo demographic transition. This transition describes the shift of a population from a state of high birth and death rates to one of low birth and death rates. Population momentum occurs during the later stages of this transition, specifically when death rates have declined, and birth rates begin to fall but are still high enough to produce large young cohorts. As the large young generations age beyond their reproductive years and fertility rates remain consistently low, the age structure of the population gradually adjusts. This shift leads to a slowing of population growth, eventually resulting in stabilization or even decline.