1. The Demographic Transition
2.1
ESE 200 Earth Systems
Prof. Jonathan Tomkin

2. Life expectancy Thomas Eakins, The Agnew Clinic
From reading we know that in 1900, life expectancy at birth was 47 years in the United States and between 45 and 50 years in Europe, Japan, and Australia. This changed quickly over the century: U.S. life expectancy at birth shot up to 68 years by 1950 and reached 77 years by 2000, and life expectancies in Europe, Japan and Australia are higher still. This increase was due to many factors, including better medical care – note the standard of care available near the end of the 19th century in this painting – it is very different from a modern operating theatre.
Thomas Eakins, The Agnew Clinic

3. Life expectancy Thomas Eakins, The Agnew Clinic
From reading we know that in 1900, life expectancy at birth was 47 years in the United States and between 45 and 50 years in Europe, Japan, and Australia. This changed quickly over the century: U.S. life expectancy at birth shot up to 68 years by 1950 and reached 77 years by 2000, and life expectancies in Europe, Japan and Australia are higher still. This increase was due to many factors, including better medical care – note the standard of care available near the end of the 19th century in this painting – it is very different from a modern operating theatre.
Thomas Eakins, The Agnew Clinic

4. Different population patterns
This increase in life expectancy (or, equivalently, decrease in the death rate) produced population booms. But these increases have stopped in many developed countries, indeed, some countries, such as Japan and Germany, are seeing death rates exceeding birth rates, and so are experiencing flat or declining populations (red and blue lines).
Year

5. Different population patterns
Other countries, such as Uganda and Nigeria (green and yellow lines) have rapid contemporary growth rates. Why is there a difference?
Year

6. Demographic Transition
Birth/Death Rate
Time
One way to think about population change is that it is an imbalance between the birth rate (that is, the number of births per person per year) and the death rate (the number of deaths per person per year). Consider how birth and death rates might be different now compared to the past. The higher life expectancies of today would translate to a lower the death rate – if we live twice as long, then the average death rate is cut in half.

7. Demographic Transition: Stage 1
Birth/Death Rate
Birth Rate
Death Rate
Time
For most of human history, the population has been relatively stable. High birth rates (green line) were offset by high death rates (red line) – many children died before reaching adulthood, and disease and famine were widespread. Life expectancies were lower than today, but on average more children were born to each mother.

8. Demographic Transition: Stage 2
Birth/Death Rate
Birth Rate
Population increase
Death Rate
Time
As living conditions improved – first in Europe in the 17th century – the death rate plunged, as improved living conditions, medicine, public sanitation, and nutrition reduced the rate of mortality. The birth rate does not at first change – people accustomed to having large families continue to do so. This leads to a population increase (shown as the difference between the death and birth rates, in blue) as more children reach adulthood.

9. Demographic Transition: Stage 3
Birth/Death Rate
Birth Rate
Population increase
Death Rate
Time
Eventually, birth rates decrease as families manage their size in the context of lower death rates. A number of reasons for this decrease in birth rates has been suggested, such as urbanization and industrialization, but it remains somewhat mysterious. During this period, incomes historically increased, which would allow for more children, not less. And this birth rate decrease was observed in Europe before effective birth control technology became widely available.

10. Demographic Transition: Stage 4
Birth/Death Rate
Birth Rate
Population increase
Death Rate
Time
Finally, a new stable population is reached, as the birth and death rates converge to a new, lower level. This stage has been observed in many modern societies, such as Western Europe and Japan. The population is higher than before the demographic transition, as the lag in the decrease in birth rates (relative to death rates) creates a one-time bump in the total population.

11. Demographic Transition: Stages 1-4
Birth/Death Rate
Stage 1
Stage 2
Stage 3
Stage 4
Birth Rate
Population increase
Death Rate
Time
It appears that many developing countries are following this trajectory, with an initial decrease in the death rate followed some time later with a decrease in the death rate. Most countries, such as Germany or Japan, are yet to reach stage 4, and some advanced economies, such as the United States, have birth rates that are higher than, and not converging towards, the death rate.

12. Demographic Transition Stages for the UK40
Birth Rate 30
Birth/Death rate, per 1000 population 20
Death Rate 10
1700
1750
1800
1850
1900
1950
2000
Here is an example of the demographic transition, for the UK. Note that the birth/death rate in the mid-18th century was around 35 per 1000 people (so between 3 and 4% of all people died in a given year). After this, death rates dropped, reaching a low of around 12 per thousand in the mid to late 20th century. Note that the birth rate remained high – in fact it wasn’t until about 150 years after the death rate went down that the birth rate followed. By 1950, the two had converged once more.
Year

13. Demographic Transition Stages for the UK40
Birth Rate 30
Birth/Death rate, per 1000 population 20
Death Rate 10
1700
1750
1800
1850
1900
1950
2000
This lag in the drop in the birth rate resulted in a large increase in the UK’s population over this time. The UK population increased from below 10 million in 1750 (the start of Stage 2) to over 50 million by the end of Stage 3. Many developing countries are still in stages 2 and 3 (if indeed they will end up following the pattern observed in the UK) – if it takes 150 years to move to stage 4 then we might expect the pressure of population growth to be with us well into the 22nd century.
Year

14. Demographic Transition in Sweden and Mexico
Birth/Death rate, per 1000 population
Year
It appears that the 20th and 21st centuries are indeed faster-paced than earlier centuries, however. Here, we can see that Sweden evolved over a similar timespan to the UK, but Mexico, a fast developing country, has had a much shorter period of transition – birth and death rates are converging in half the time. This could be due to the high rate of economic growth, rapid social change, or the efficient dissemination of family planning technology and information in modern Mexico.

15. Population growth in the 20th Century7 6 5
Total Population, Billions 4 3 2
Less Developed Countries 1
More Developed Countries
1900
1920
1940
1960
1980
2000
As a consequence of this demographic transition – the transition from high birth and death rates to low birth and death rates – the more developed countries have contributed little to the large increase in world population over the 20th century. In contrast, the less developed countries, many of which have not experienced the demographic transition, are today responsible for almost all of the Earth’s population growth.
Year