8.1A Birth and Immigration as Inputs to Population Growth Notes

Population Inputs: Births and Immigration

Population growth is influenced by two primary inputs: births and immigration.

These factors determine how a population increases over time at local, national, and global scales.

Measuring Population Inputs

Crude Birth Rate (CBR)

1. The number of live births per 1,000 people per year.
2. Higher in developing countries due to cultural, economic, and healthcare factors.

Immigration Rate

1. The number of immigrants per 1,000 people per year.
2. Driven by economic opportunities, conflicts, climate change, or political instability.

Factors Influencing Birth and Immigration Rates

Birth Rate Determinants:

1. Access to healthcare (e.g., maternal care lowers birth rates).
2. Economic development (higher income = lower birth rates).
3. Cultural norms (some societies encourage large families).

Immigration Rate Determinants:

1. Job opportunities (people migrate for better employment).
2. Conflict & instability (wars force people to leave their home country).
3. Climate change (rising sea levels displace coastal populations).

Population Outputs: Deaths and Emigration

Population size is influenced by deaths and emigration, which reduce the total number of people in a given area.

These outputs help determine whether a population is shrinking, aging, or facing sustainability challenges.

Measuring Population Outputs

Crude Death Rate (CDR)

1. The number of deaths per 1,000 people per year.
2. Higher in aging populations and regions with poor healthcare.

Emigration Rate

1. The number of people leaving a country per 1,000 people per year.
2. Driven by economic, political, and environmental factors.

Factors Influencing Death and Emigration Rates

Death Rate Determinants:

1. Healthcare quality (poor medical care = higher deaths).
2. Age distribution (aging populations have more deaths).
3. Diseases and pandemics (e.g., COVID-19 increased death rates).
4. Living conditions (pollution, war, and malnutrition raise deaths).

Emigration Rate Determinants:

1. Economic opportunities (people leave for better jobs).
2. Conflict & instability (wars force people to flee).
3. Climate change (rising sea levels and droughts drive migration).
4. Political repression (authoritarian regimes push people to leave).

Population Dynamics: Key Metrics and Calculations

1. Understanding population trends requires analyzing fertility, life expectancy, growth rates, and natural increase.
2. These metrics help in forecasting future population size and resource demands.

Key Population Metrics

Total Fertility Rate (TFR)

1. The average number of births per woman of childbearing age.
2. Replacement level fertility is ~2.1 (needed to maintain population size).

Life Expectancy

1. The average number of years a person is expected to live if current conditions remain stable.
2. Influenced by healthcare, nutrition, sanitation, and conflict.

Doubling Time (Rule of 70)

1. The time it takes for a population to double at its current growth rate.
2. Formula: Doubling Time = 70/ Growth Rate (%)

Natural Increase Rate (NIR)

1. Measures population growth, excluding migration.
2. Formula: NIR = (Birth Rate−Death Rate)/10

Why These Metrics Matter

1. High fertility + low mortality = Rapid growth → Strain on resources (e.g., India).
2. Low fertility + aging population = Workforce decline (e.g., Italy, Japan).
3. Short doubling time = Rapid urbanization & pressure on infrastructure (e.g., Nigeria).
4. Declining natural increase = Need for immigration & policy changes (e.g., Canada).

Global Human Population Growth & Future Projections

The human population has experienced exponential growth, especially after the Industrial Revolution.

To predict future trends, models like UN population projections estimate different scenarios based on fertility rates.

Understanding Population Growth Trends

Past Growth Trends

1. Pre-1800: Slow growth due to high mortality.
2. 1800–1950: Rapid growth with industrialization and medical advances.
3. 1950–2020: Exponential growth from ~2.5 billion to 8 billion.

Future Growth Uncertainty

1. Population may peak in the late 21st century.
2. Fertility rates are declining globally, but at different rates across regions.

UN Projection Models: Three Scenarios

The UN uses three fertility scenarios to predict global population growth:

High Fertility Scenario:

1. Fertility remains high (~2.5 births per woman).
2. Population could exceed 15 billion by 2100.
3. More pressure on food, water, and energy resources.

Medium Fertility Scenario (Most Likely):

1. Fertility declines to ~2.1 (replacement level).
2. Population stabilizes around 10.4 billion by 2080.
3. Requires continued education, healthcare, and economic improvements.

Low Fertility Scenario:

1. Fertility drops below replacement level (~1.5 births per woman).
2. Population peaks around 8–9 billion and declines after 2060.
3. Causes aging populations, labor shortages, and economic shifts.

Factors Influencing Future Growth

1. Education & Women’s Empowerment → Higher education reduces fertility.
2. Economic Development → Urbanization & cost of living lower birth rates.
3. Healthcare Improvements → Lower child mortality means fewer births needed.
4. Government Policies → Incentives for childbirth or restrictions (e.g., China’s past one-child policy).