The United Nations predicted the world's population will jump to 11.2 billion by 2100 from the current 7.6 billion.
The population rose by a billion since 2005; the latest projections suggest it will rise by another billion by 2030 and over two billion by 2050.
The UN's population division also forecasted India's population will surpass China's in the next seven years.
What will happen to the world by 2030?
The world's populous country
Currently, China is the most populous country in the world with a population of 1.41 billion.
However, India and China are estimated to have an equal population of 1.44 billion each by 2024.
After that, the population of India will continue to grow, while that of China will remain stable through 2030s and then would decline.
What about India?
Predictions for population growth of India
'World Population Prospects: The 2017 Revision' published by the UN Department of Economic and Social Affairs raised the earlier predictions of population growth.
It projected that the population of India, currently standing at 1.34 billion, will grow to 1.51 billion by 2030 and 1.66 billion by 2050.
It is estimated to decline to 1.52 billion by the end of century.
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Nine countries to account for half the growth
In 2047, Nigeria will remarkably surpass the US and become the third most populous country.
Nigeria's current population is 191 million while that of the US is 324 million.
Difficult Art: Several factors considered for predicting population
To predict the population growth, several factors are considered.
It includes fertility rates in different regions, mortality rates, and population momentum, the newest addition.
In Europe, the fertility rate increased from 1.4 to 1.6.
Importance of fertility rates in estimating populations
The report illustrates the importance fertility rates in different regions for estimating future populations.
It stated 83 nations have fertility rates below the 'replacement level' taken as 2.1.
The replacement level is the birth rate at which a population replaces itself without any migration in one generation.
Many countries, including China and US, are witnessing fluctuations with occasional dips and rises.
Dropping fertility rates lead to aging societies
Declining rates of fertility have led to the phenomenon of societies with elderly population.
Currently, there are 962 million people in the world aged 60 or above; the number is estimated to more than double by 2050 and triple by 2100.
The rise in life expectancy by four years in only a decade is the reason behind aging societies.
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