PYTR Class

Learning Objectives

1. Outline how rapid population growth stresses the environment
2. Describe population momentum
3. Explain environmental causes leading to environmental migration

Rapid human population growth has increased stress on the Earth’s systems

The increasing pressure exerted on Earth’s systems as a result of rapid human population growth is closely linked to biocapacity disparities and to the transgression of both social foundations and planetary boundaries within the Doughnut Economics framework. The principal drivers of population growth include changes in fertility, mortality, and migration patterns. The global human population reached approximately 8 billion in 2022, and United Nations projections suggest that it will stabilise between 10 and 11 billion by 2100. However, population growth may not reach this level, as fertility rates tend to decline with rising levels of education and wealth.

Reductions in fertility may also arise from broader developmental improvements, many of which are promoted through the United Nations Sustainable Development Goals (SDGs). For example, improved access to clean water and advances in food production reduce child mortality, thereby diminishing the perceived need for larger families to offset expected deaths. Consequently, some organisations suggest that global population growth may peak as early as 2060.

Earlier projections illustrate the uncertainty inherent in long-term demographic forecasting. In 1992, the United Nations published long-range population projections estimating a high scenario of 23 billion, a medium scenario of 11 billion, and a low scenario of just 5 billion. These estimates differ substantially from current projections and reflect earlier assumptions that fertility rates in low-income countries would remain persistently high. As fertility rates have declined, contemporary population projection models predict substantially lower future population levels. This highlights that the further projections extend into the future, the greater their uncertainty and imprecision.

Population growth, combined with the expanding number of middle- and high-income households, places considerable pressure on environmental systems. Rising affluence intensifies these pressures through increased demand for freshwater, energy, and resource-intensive food products such as meat and dairy, which require more land than arable crop production. Fossil fuels continue to be consumed in large quantities, forests are cleared for timber, fuel, and agricultural expansion, and human activities contribute significantly to environmental pollution.

Biocapacity, or biological capacity, refers to the ability of ecosystems, or the Earth as a whole, to provide goods and services essential for human survival and well-being. These include tangible goods such as food, water, and timber, as well as ecosystem services such as climate regulation and flood control. An increase in human population reduces available biocapacity per capita, thereby intensifying ecological strain.

Age—sex pyramids can be used to determine dependency ratios and population momentum

Age–sex pyramids are valuable demographic tools that can be used to analyse dependency ratios and population momentum. The dependency ratio compares the number of dependants—typically defined as non-working individuals aged under 15 years and over 64 years—with the economically productive population aged 15 to 64 years. Dependency ratios tend to be high in populations characterised by either very high fertility rates, which result in a large proportion of young dependants, or very low fertility rates, which lead to population ageing and an increasing proportion of elderly dependants.

Population momentum refers to the tendency for a population to continue growing even after fertility rates have declined. This occurs because population growth is influenced not only by the number of children born per woman but also by the size of the cohort of women of reproductive age. Population momentum is particularly evident when there is a substantial bulge in the youthful population that has yet to enter its reproductive years. For example, during China’s one-child policy (1980–2016), the population continued to increase and is projected to peak in the 2030s, despite total fertility rates remaining below the replacement level of 2.1 for several decades. At the onset of the policy, approximately one-third of China’s population was under the age of 15, contributing to sustained population growth. In contrast, negative population momentum occurs when, despite an increase in total fertility rates, the number of individuals within reproductive age cohorts has declined, resulting in fewer births overall.

Reasons for patterns and trends in population structure and growth

Patterns and trends in population structure and growth vary considerably between countries due to a combination of historical, cultural, religious, economic, social, and political factors. As a result, countries such as Ethiopia and the United States exhibit markedly different demographic profiles and trajectories.

Environmental factors are also increasingly influencing migration patterns. Environmental migration may arise from climate change and sudden-onset events such as flooding, droughts, wildfires, and intensified storms. In addition, slow-onset processes—including desertification, sea-level rise, and saltwater intrusion—are becoming more significant drivers of migration. For instance, repeated cyclones in Mozambique have caused widespread destruction and prompted emigration, while rising sea levels and other climate-related impacts have contributed to increased migration from Tuvalu to New Zealand.

Case Study

Tuvalu is an island group and Kiribati isan atoll

1. Using a map, locate where Kiribati and Tuvalu are located.
2. Summarise information about these two places using the following table:

	Tuvalu	Kiribati
Population size
Population growth rate
GDP/capita (USD)
Carrying capacity (people/km2)
Employment structure

• Explain how climate change affects these two islands which ultimately forces population to migrate
• State the usual migration destination
• Outline three reasons of emigration being difficult
• Outline some suggestions to make emigration easier