Environmental Science / Unit 4: Populations
4.5 Human Population Growth
Notes
The human population passed 8 billion in 2022. It took until about 1804 to reach 1 billion, but recent billions took only 12 to 15 years.
- Growth accelerated because of improved sanitation, medicine, vaccines, and agricultural productivity, which lowered death rates.
- Crude birth rate (CBR) and crude death rate (CDR) are births and deaths per 1,000 people per year. Natural growth rate (%) $\displaystyle = \frac{\text{CBR} - \text{CDR}}{10}$.
- Total fertility rate (TFR) is the average number of children per woman. Replacement level fertility is about 2.1.
- Example: CBR = 30 and CDR = 10 gives $\displaystyle \frac{30 - 10}{10} = 2\%$ per year, so doubling time $= 70 \div 2 = 35$ years.
- Infant mortality rate and the education of women strongly influence fertility.
Practice
A country has a birth rate of 24 per 1,000 and a death rate of 9 per 1,000. What is its natural growth rate (ignoring migration)?
$\displaystyle \frac{24 - 9}{10} = 1.5\%$.
Using the rule of 70, how long will the population of the country above take to double?
$70 \div 1.5 \approx 46.7$ years.
What is replacement level fertility?
A little above 2 replaces both parents and allows for early deaths.
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