There are currently near 6.800 million people on the planet. Never before has the world population rate been so high. Thus, it is, by now, the maximum number that has been ever reached, as the result of a continuous growth.
Although there can be defined several stages of the humanity where the population growth has been significant, as the one that has been emphasised by the American ecologist Edward Deevey, which occurred due to the agriculture appearance within the Neolithic Revolution, there is no doubt that the starting point for the current number is the Industrial Revolution (second half of the 18th century), which caused an exponential demographic growth in a short period of time. This growth, which has taken place in the last 250 years of the human history, covers everything that occurred in the previous hundreds of thousands of years.
In the Lower Palaeolithic era, world population is estimated to have reached about 125.00 inhabitants, all of them living in Africa. The rate of one million inhabitants has been reached over 300 thousand years ago, during the Middle Palaeolithic, when Eurasia was already settled; and the five million one, 10 million years ago, when all the continents were populated. At the beginning of the Christian era, the world population consisted of about 300 million inhabitants and in the year 1000, there were 310 million. Later, in some periods of the Middle Ages, the population growth stopped and had even been reversed by the significant food crisis, caused by several climatological factors and wars that gave place to hunger, epidemics and subsequent high mortality.
Some 250 years ago, the world population consisted of about 800 million inhabitants, and from that moment, it has progressively increased, until the mid-fifties in a continued, but steady way, and since that date, in an exponential way. In this manner, in the last 25 years, the population has increased so much, as never before in the whole history.
In order to understand the growth rhythm, often it is not enough to simply observe the difference between the population volumes in different periods of time; so, showing the growth in relative numbers is even more interesting.
Thus, the best indicator that would better measure the rhythm of the population growth is the compound annual growth rate (CAGR). It is called ‘compound’ because the starting point idea is considering, at the beginning of every year, not only the initial population, but also the growth that has been experimented until that moment. Accordingly, the growth always depends on the population volume of the every new year beginning, so its overall magnitude will also change. For this reason, the CAGR is also called a ‘geometric growth’ indicator, instead of a simpler growth rates ‘arithmetic growth’ one.
The above formula shows that the compound annual growth rate has steadily maintained at around 4-5‰, from the beginning of the 19th century until the beginning of the 20th century. Since that moment, the world population growth has noticeably increased with 15-20‰ annually, although there have been some oscillations.
Due to this growth, the needed years for the world population rate to double have decreased considerably, from 100 years —or more— to 40-45 years currently.
ASo, if we take, for instance, the year 1500 population data of about 500 million inhabitants, we can observe that it has doubled only after near 300 years, as world population hasn’t reached the 1000 million inhabitants rate, as we know, until the mid-19th century. On the other hand, it only took roughly 150 years (around the thirties) to reach the 2000 million inhabitants, and roughly 45 years, to double this last rate and reach the 4000 million inhabitants.
In the last decades, this duplication rhythm growth of the world population has noticeably slowed: whereas with the maximum growth rhythm —approximately between 1960 and 1970— the population would have doubled in a little less than 30 years, currently, this rate increased until 60 years, as a result of the mentioned growth rhythm decrease, showed with the CAGR formula.
Link to watch the world population: