Human Population Dynamics (DP IB Environmental Systems & Societies (ESS))

Demographic Variables

Inputs to human populations: births and immigration

• Births and immigration are inputs that contribute to the growth of a population

• Crude birth rate (CBR):

  • This is the number of live births per 1 000 people in a population per year

    • For example, a CBR of 15 means 15 babies are born for every 1 000 people in that population each year

  • CBR is calculated by dividing the total number of live births in a year by the total population and then multiplying by 1 000

• Immigration rate:

  • This is the number of immigrants per 1 000 people in a population per year

Outputs from human populations: deaths and emigration

• Deaths and emigration are outputs that reduce the size of a population

• Crude death rate (CDR):

  • This is the number of deaths per 1 000 people in a population per year

    • For example, a CDR of 8 means 8 people die for every 1 000 people in that population each year

  • CDR is calculated by dividing the total number of deaths in a year by the total population and then multiplying by 1 000

• Emigration rate:

  • This measures the number of people leaving a population per 1 000 people per year

Quantifying population dynamics

• Population growth and decline can be quantified through several key measures:

• Total fertility rate (TFR):

  • This is the average number of children a woman is expected to have during her lifetime, based on current age-specific fertility rates

    • In developing countries, TFR tends to be higher (e.g. due to limited access to family planning)

  • TFR is calculated by summing the age-specific fertility rates (ASFR) and multiplying the result by five

• Life expectancy:

  • This is the average number of years a person is expected to live from birth, assuming current demographic factors (such as healthcare) remain the same

• Doubling time (DT):

  • This is the number of years it would take a population to double in size, based on its current growth rate

  • DT is calculated using the 'rule of 70': divide 70 by the population growth rate percentage

• Natural increase rate (NIR):

  • This is the difference between the crude birth rate and crude death rate, usually expressed as a percentage or a number per 1 000.

    • If the birth rate is higher than the death rate, natural increase occurs

  • NIR is calculated by subtracting the CDR from the CBR and then dividing the result by 10

Human Population Growth

Rapid growth of the global human population

• The global human population has followed a rapid growth curve, particularly in the past century

  • The global human population grew very slowly until 18th century

  • From 10 000 BCE to 1700 CE, the average growth rate was just 0.04% per year

  • There has been exponential growth in the global human population since the mid 18th century

  • In 1800, the world population was about 1 billion

  • By 2024, the population will have grown to over 8 billion

  • This growth is largely due to improvements in medicine, agriculture and technology, which have reduced death rates

• The growth rate is starting to fall again

• However, the world population is projected to continue to grow until approximately 2100, when it could reach more than 11 billion

Models to predict future global population growth

• Population models are used to predict the growth of the human population in the future

  • These models take into account birth rates, death rates, fertility rates, and migration

  • Models can help policymakers understand trends and make decisions about resource use, healthcare and urban planning

UN projection models

• The United Nations (UN) uses models to project future global population growth, offering three different scenarios:

  1. High-fertility scenario: assumes higher birth rates will continue, leading to a more rapid population increase

  2. Medium-fertility scenario: assumes a steady decline in fertility rates, leading to moderate population growth (this is the most likely scenario)

  3. Low-fertility scenario: assumes fertility rates will drop significantly, leading to slower growth or a shrinking population

• By 2100, the global population is projected to be around 9.7 billion in the medium-fertility scenario

Uncertainty of future fertility rates

• Predicting fertility rates is challenging, leading to uncertainty in population forecasts

  • Changes in cultural norms, economic conditions, and government policies can all influence fertility rates

• Countries that went through Industrial Revolutions in the 18th and 19th centuries experienced rapid population growth

  • Today those countries are developed and their growth rates have fallen

  • In some cases, they have fallen so much that their total populations are in decline (e.g. Japan)

• The fastest population growth today occurs in developing countries that are rapidly industrialising