The knowledge and the understanding of which has been the evolution of the Earth inhabitants’ number are essential elements, if we deal with the sustainable development matter.
In fact, the first principle of the 1992 Rio de Janeiro Declaration on Environment and Development states that: ‘Human beings are at the centre of concerns for sustainable development. They are entitled to a healthy and productive life in harmony with nature.
At the same time, the population, its growth and the economic growth are significant human causes of climate change: as the population grows, its natural resources needs also grow; as a result, the development becomes unsustainable.
In geographical terms, the growth occurs due to two factors: natural movement, which is simply the difference between the birth rate in relation to the death rate of a specific region; and migratory movement, which is the difference between the emigration and the immigration volume.
Although both of these elements act, more or less, independently of each other, obviously, there are certain interrelations and, sometimes, the growth of one of them can take place because of the decrease of the other one, or vice versa. Thus, there is positive growth when the balance between both of them is positive and negative growth when the balance is negative.
- Positive growth
- Negative growth
As our world is a ‘closed’ system that has no entrances and exits to or from the outside, it is obvious that at planetary scale, the only factor that determines the population growth is the natural movement. On the other hand, at smaller scales (regional or state level), the population evolution may be conditioned by one factor, another one, or by both of them; thus, the importance of each of them depends on the territory that is being analysed. Actually this is the main idea of the compensatory equation, which shows that the growth is the result of the sum between the natural movement and the migratory movement:
Growth = Birth rate – Death rate + Immigration – Emigration
Growth= Natural Movement + Migratory Movement
The following chapters are aimed to measure the recent world population growth and its future trends, in a didactic way.