Every two years, the United Nations Population Division issues a new revision of World Population Prospects, the official set of United Nations population projections. Frequent revisions are necessary because, as new data on population dynamics at the country level reach the United Nations, past estimates of population trends are often found to need revision. Since the methods currently used to produce the UN projections rely on past trends to derive future population paths, changes to past estimates induce changes in the projected future. In particular, modifications to the most recent estimates of fertility, mortality, and population size considerably impact the projection results obtained.
In July, the United Nations Population Division released the 2015 Revision, which updates the 2012 Revision issued in 2013. Both Revisions use essentially the same methodology and both include a set of deterministic projections—where analysts make explicit decisions about the future paths of fertility, mortality, and migration—and a set of probabilistic projections where models simulate thousands of different paths and thus permit an assessment of future uncertainty underlying the projected results.
According to the 2015 Revision, the world today has 7.3 billion inhabitants and a 95-percent chance of having between 9.5 billion and 13.3 billion in 2100. Furthermore, there is just a 23-percent chance that the world population may peak and start declining before 2100. The median projected population for 2100 is 11.2 billion, meaning that there is a 50/50 chance that the population at century’s end may actually be higher or lower than that number.
Comparing the 2015 Revision with the 2012 Revision
The 2012 Revision projected a median population in 2100 of 10.9 billion—359 million lower than that projected by the 2015 Revision. This difference is made up of discrepancies between the two Revisions in the starting population and the numbers of births and deaths projected. The 2010 population, which was the starting point for the 2012 Revision, is higher in the 2015 Revision by nearly 14 million. Between 2010 and 2100, the number of births projected in the 2015 Revision surpasses that projected in the 2012 Revision by 194 million and the number of deaths is lower by 152 million. That is, the median path (also called the “medium variant”) of the 2015 Revision projects higher fertility and lower mortality than the 2012 Revision did.
The differences in total fertility between the 2015 and the 2012 Revisions are highest during 2010-2030 and are strongly influenced by the upward revision of total fertility in 2005-2010, when the total fertility of the least developed countries in particular underwent a substantial revision, increasing by a tenth of a child. At the same time, the 2015 Revision revised mortality downward for both 2005-2010 and 2010-2015, leading to a noticeable shift to lower mortality in comparison to that of the 2012 Revision over the whole projection period. Consequently, between 2010 and 2050, the reduced mortality of the 2015 Revision with respect to that of the 2012 Revision contributes more to accelerate population growth than the upward revision of fertility. Because most of the additional reductions of mortality projected by the 2015 Revision occur in the adult ages, they contribute indirectly to increase the number of births by increasing the population of reproductive age. After 2050, the contribution of excess births in the 2015 Revision in relation to the 2012 Revision vastly surpasses the contribution made by fewer deaths to increase population growth above that projected by the 2012 Revision.
These results indicate that, if mortality decline accelerates as projected in the 2015 Revision, it is all the more urgent to accelerate also the reduction of fertility in those countries that still have high levels in order to reduce the potential of higher population growth and increase the chances of reaching a peak population before 2100.
Key Results of the 2015 Revision
The medium variant of the 2015 Revision projects a world population of 8.5 billion in 2030 and 9.7 billion in 2050. The 95-percent confidence interval for 2030 ranges from 8.4 billion to 8.6 billion, whereas that for 2050 is wider: from 9.3 billion to 10.2 billion. To achieve the medium variant, fertility in the least developed countries has to decrease from its current 4.20 children per woman to 3.46 children per woman in 2025-2030 and to 2.87 in 2045-2050. Similarly, the remaining developing countries must reduce their fertility from 2.36 today to 2.09 in 2045-2050. Slower reductions will produce larger future populations if mortality declines as projected.
Assuming that the medium variant is realized, the world population will increase by 2.4 billion between 2015 and 2050, 1.3 billion of which will be added to Africa and 0.9 billion to Asia. The population of developed countries as a group will barely increase, mostly because of migration, and that of Europe will decrease. Africa’s share of the world population will rise from 16 percent in 2015 to 25 percent in 2050, while that of Asia will fall and so will that of developed countries (see table).
Population aging will continue and the proportion of persons aged 60 or over will rise from 12 percent today to 22 percent in 2050. Africa will remain the region with the youngest population, with the share of those aged 60 or over rising from 5 percent today to 9 percent in 2050. However, to achieve such slow population aging, Africa will have to maintain a rapid rate of population growth, averaging well above 2 percent per year until 2040.
Globally, the number of children under 15 and young people aged 15 to 24 will increase from 1.9 billion and 1.2 billion, respectively, to 2.1 billion and 1.3 billion in 2050. Africa, which accounts for 25 percent of the world’s children and 19 percent of the world’s young people today, will account for 39 percent and 34 percent, respectively, in 2050 and will be the only region with an increasing population of children and youth at mid-century. More than any other region, therefore, Africa will face the challenges of educating ever-increasing numbers of children and of generating jobs for ever-increasing numbers of young people.
The full results of the 2015 Revision can be accessed at www.unpopulation.org.