In 50 to 100 years of time, the world population could eventually be represented by a structure of a high-rise building, meaning more number of living adults than any other time
From a pyramid to a dome to a high-rise building. This is not any lesson in architecture, but rather how the age structure of the world's population is evolving.
The population pyramid — a preferred way to represent and visualise the demographic of a population — is no longer accurate. It has turned into a dome or a bell. And in 50 to 100 years of time, the world population could eventually be represented by a structure of a high-rise building.
Source: Der Spiegel/Statista
Why a pyramid?
In order to explain why the world population during a large part of the 1900s (and before) was shaped like a pyramid and not some other shape, we need to understand the gap in supply and depletion. As a percentage of people died from rampant diseases and other reasons in every age group, the groups at the top registered less number of people than groups below it.
For example, if there are 1,000 people in the age group 10-14 years and 100 of them die, after the five years the next age group i.e. 15-19 years would receive only 900 people (the people in this age group would have moved to the next group in the same amount of time) and so on. Thus, if all age groups are represented by bars (separately for males and females) and stacked one above another, this would result in a step-like structure i.e. a pyramid.
Why the change in shape?
According to an estimate, the world is adding a net of 80 million (birth minus death) each year to its population, as the growth is at a record level. So, the pyramid should only expand both sides at the base, not change its shape, right?
The answer to this question is provided by World Bank Economist Wolfgang Fengler. He says, “...today’s rapid population growth is driven by longevity, and no longer by high fertility: there are more and more adults in the world. This is why we can experience both declining fertility and rapid population growth at the same time.”
From 1970 to 2015, the population of age group 0-19 years grew 42 percent whereas the population aged 20-39 rose by 128 percent. Better medical facilities and increasing life expectancy has expanded the top bars in the population pyramid. Comparatively, the bottom bars, belonging to 0-30 age group has seen very little expansion. This has reflected in the change of the structure from pyramid to bell.
Proponents of pyramid structure reason it to be the ideal age structure as in any society it ensures that there are lots of industrious young men and women and few dependent old people. In many less developed or developing countries (including India), the age structure still forms the shape of a pyramid.
According to the 2011 Census, the population distribution in India more or less still represents the pyramid figure. However, the bottom two bars, i.e. population below 10 years are less than the population of the age group of 10 and above. This shows that in post-2000 India, the birth rate has been in check.
By the turn of the 21st century, the bell shape will move towards the shape of a high-rise building, as the life expectancy would increase for developed countries. There would be little difference in the population of age groups above 40 years.
According to calculations by Fengler, by 2050, there will be an additional 2.2 billion people in the world, bringing the total to approximately 9.5 billion. The growth will be as follows:
Children and teenagers (0-19 years) will remain the largest group but only grow modestly from 2.5 billion to 2.7 billion (an increase of 8 percent);
Young adults and parents (20-39 years) will only see modest changes (the biggest shifts in this group already happened over the last 30 years) growing from 2.2 to 2.6 billion (a 14 percent increase);
The "new middle aged" (40-59 years) will experience major growth. rising from 1.7 billion today to 2.2 billion in 2050 and this group will add more than half a billion people (plus 38 percent);
The grandparents (60-79 years) will gain the most and more than double in size from 760 million to 1.6 billion (a 100 percent increase);The new “oldies” (80+) are also expected to rise sharply but from a very low base. From 120 million today, they should add another 380 million by 2050 (plus 211 percent).