The main reason for the adjustment is increased population growth in India and Africa.

The UN Department of Economic and Social Affairs published its "World Population Prospects: The 2017 Revision" on Wednesday, raising its previous predictions for population growth from 8.5 billion by 2030 and 9.7 billion in 2050.

The world's population will grow to 8.6 billion in 2030, 9.8 billion in 2050 and 11.2 billion in 2100, driven by faster growth in African countries, according to forecasts by the United Nations.

India is currently the second most populous country in the world with with 1.3 billion inhabitants, compared to China's 1.4 billion, but India's population is expected to surpass China's by 2024.

Meanwhile, Africa is experiencing continued high rates of population growth. The UN report predicts, between 2017 and 2050, the populations of 26 African countries will expand to at least double their current size.

"The population of Africa is notable for its rapid pace of growth. It is anticipated that over half of global population growth between now and 2050 will take place in that region," said Jon Wilmoth, director of UN's population division, during a press briefing on Wednesday.

"At the other extreme, it is expected that the population of Europe will decline somewhat in the coming decades."

Despite lower fertility rates in nearly all regions of the world (total fertility rates in Africa slowed from 5.1 births per woman between 2000 and 2005 to 4.7 in 2010 to 2015), life expectancy is higher worldwide; global life expectancy has risen from 65 years for men and 69 years for women in 2000 to 2005, to 69 years for men and 73 years for women in 2010 to 2015.

This will lead to older populations, with more people surviving into old age. This will create challenges and opportunities, according to Wilmoth.

For instance, countries with growing populations will experience a concentration of people of working-age, leading to a rapid growth of income per capita.

"On the other hand, in countries with rapidly growing older populations, the upward shift in the age distribution challenges the sustainability of social protection systems, especially old‐age pension and health care systems, due to a decreasing ratio of workers to retirees," he warned.

The UN report predicts that by 2050, half of the world's population growth will be concentrated in just nine countries: India, Nigeria, the Democratic Republic of the Congo, Pakistan, Ethiopia, the United Republic of Tanzania, the U.S., Uganda and Indonesia.

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