Population pyramids show the structure of a population by comparing relative numbers of people in different age groups. Population structures differ markedly between LEDCs and MEDCs.
Demographic transition models show population change over time - and also show marked differences between LEDCs and MEDCs.
At present the world's population is growing quickly, though this has not always been the case.
- Until the 1800s the world's population grew slowly for thousands of years.
- In 1820 the world's population reached one billion.
- In the early 1970s, the world's population reached three billion.
- In 1999, less than 30 years later, the population doubled to six billion.
- The global rate of population growth is now one billion every 15 years.
The graph shows this pattern of accelerating growth (including the predicted population for 2025).