Human Population

Module 7 (10/13–10/19) · Human Population · Blueprint Pillar 3 · PGCC Outcome 3 · Download .docx

Objectives

Describe the demographic transition model and its four stages.
Interpret an age structure diagram.
Apply the IPAT equation to assess environmental impact.
Explain population momentum.

Key terms

Demographic transition model: Four-stage model of population change as societies industrialize, from high birth/death rates to low birth/death rates.
Total fertility rate (TFR): Average number of children a woman in a population has over her lifetime.
Replacement-level fertility: TFR of ~2.1 at which a population neither grows nor shrinks over time.
Age structure diagram: Population pyramid showing the number or proportion of individuals in each age and sex group.
Rule of 70: Divide 70 by the annual growth rate to estimate doubling time in years.
IPAT equation: I = P × A × T: Environmental Impact = Population × Affluence × Technology.
Urbanization: Shift in population from rural to urban areas as societies develop economically.
Infant mortality rate: Number of deaths of children under 1 year of age per 1,000 live births per year; key indicator of development.
Doubling time: The number of years required for a population to double at its current growth rate.
Population momentum: Continued population growth after TFR drops to replacement level, due to large numbers of young people entering reproductive age.
Stage 2 (DTM): Demographic transition phase with high birth rate and falling death rate — period of rapid population growth.
Stage 4 (DTM): Demographic transition phase with low birth and death rates — population near zero growth or declining.

The concept

Global human population reached 8 billion in 2022. Growth was slow for most of history, then accelerated sharply after the Industrial Revolution as improved food, medicine, and sanitation reduced death rates faster than birth rates fell — the Stage 2 population boom in the demographic transition model.

The demographic transition model (DTM) describes four stages of population change. Stage 1: high birth and death rates, small population. Stage 2: birth rates high, death rates falling — rapid growth. Stage 3: birth rates falling, low death rates. Stage 4: low birth and death rates, near-stable population. Most future growth is projected in nations still in Stages 2–3.

The IPAT equation ties population to environmental damage: I = P × A × T (Impact = Population × Affluence × Technology). A population age structure diagram with a wide base signals a young, growing population; a narrow base signals an aging one. The rule of 70 estimates doubling time: divide 70 by the annual growth rate. Population momentum explains why growth continues even after fertility drops to replacement level — large youth cohorts are still moving through reproductive age.

Self-check

Try each one before you look. A miss here costs nothing and tells you exactly what to reread.

1. Stage 2 of the demographic transition is characterized by:

2. A country with a wide-based, triangular age structure diagram most likely has:

3. Using the rule of 70, a country with a 2% annual population growth rate will double its population in approximately:

4. The IPAT equation (I = P × A × T) shows that environmental impact depends on:

5. Population momentum explains why a nation's population continues to grow even after:

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