The United Nations said Wednesday that the world population is expected to reach 8.6 billion in 2030, and to hit 9.8 billion by 2050, despite nearly universal lower fertility rates.
The world population is now at least 7.6 billion, up from 7.4 billion last year, spurred by the relatively high levels of fertility in developing countries -- despite an overall drop in the number of children people have around the globe, revealed World Population Prospects: The 2017 Revision.
The concentration of global population growth is in the poorest countries, presenting a challenge as the world seeks to implement the 2030 Sustainable Development Agenda, which is aimed to end poverty and preserve the planet, according to the report.
"With roughly 83 million people being added to the world's population every year, the upward trend in population size is expected to continue, even assuming that fertility levels will continue to decline," said the UN Department of Economic and Social Affairs, which produces the UN report.
At this rate, the world population is expected to reach 8.6 billion in 2030, 9.8 billion in 2050 and surpass 11.2 billion in 2100, it said.
The growth is expected to come, in part, from the 47 least developed countries, where the fertility rate is around 4.3 births per woman, and whose population is expected to reach 1.9 billion people in 2050 from the current estimate of 1 billion.
In addition, the birth rates in African countries are likely to "at least double" by 2050, said the report.
That trend comes despite lower fertility rates in nearly all regions of the world, including in Africa, where rates fell from 5.1 births per woman up to 2005 to 4.7 births in the five years following.
In contrast, the birth rates in Europe are up to 1.6 births per woman, up from 1.4 births in 2000-2005.
"During 2010-2015, fertility was below the replacement level in 83 countries comprising 46 per cent of the world's population," said the report.
The lower fertility rates are resulting in an ageing population, with the number of people aged 60 or over expected to more than double by 2050 and triple by 2100, from the current 962 million to 3.1 billion.
Africa, which has the youngest age distribution of any region, is projected to experience a rapid ageing of its population, the report noted.
"Although the African population will remain relatively young for several more decades, the percentage of its population aged 60 or over is expected to rise from five per cent in 2017 to around nine per cent in 2050, and then to nearly 20 percent by the end of the century," according to the report.
In terms of other population trends depicted in the report, the population of India, which currently ranks as the second most populous country with 1.3 billion inhabitants, will surpass China's 1.4 billion citizens, by 2024.
By 2050, the third most populous country will be Nigeria, which currently ranks seventh, and which is poised to replace the United States.
Meanwhile, the report also noted the impacts of migrants and refugees between countries, in particular noting the impact of the Syrian refugee crisis and the estimated outflow of 4.2 million people.
In terms of migration, the report said, "although international migration at or around current levels will be insufficient to compensate fully for the expected loss of population tied to low levels of fertility, especially in the European region, the movement of people between countries can help attenuate some of the adverse consequences of population ageing."