The numbers are up: The latest projections from the UN Population Division estimate that world population will reach 9.3 billion by 2050 – a slight bump up from the previous estimate of 9.1 billion. The most interesting change however is that the UN has extended its projection timeline to 2100, and the picture at the end of the century is of a very different world. As opposed to previous estimates, the world’s population is not expected to stabilize in the 2050s, instead rising past 10.1 billion by the end of the century, using the UN’s medium variant model.

Africa is projected to experience the most explosive increase in size: the population of sub-Saharan Africa will nearly quadruple, growing from 856 million in 2010 to 3.3 billion by 2100. Nigeria alone is projected to be home to 730 million people – nearly equal to the entire population of Europe today (738 million) and four and half times its current size. The Republic of Tanzania will be the fifth most populous country in the world, with 316 million people.

In contrast, Europe as a whole is projected to shrink to 675 million by around 2080, before leveling off. China, Japan, and South Korea are also projected to decline in size, with India passing China in 2021. The United States is projected to maintain steady growth, eventually reaching 478 million people in 2100.

“A Wake-up Call”

The 2010 revision’s numbers are different due to changes in the UN’s methodology that take into account slower than previously expected declines in total fertility (number of children born to a woman during her lifetime), more accurate, country-specific estimates, and longer life expectancy. Elizabeth Leahy Madsen of Population Action International writes on Grist:

The UN has shifted to a “probabilistic” model for its medium-fertility scenario. This allows the pace of each country’s fertility decline to be calculated individually, based on new estimates of historic fertility rates, allowing for much more variance across countries. The new method also assumes that fertility rates will eventually balance out around 2.1 children per woman, a level where couples would “replace” themselves in the population, rather than 1.85. And the projections now extend out to 2100, and incorporate life expectancies ranging as high as 90+ years.

In particular, these changes created much higher estimates for sub-Saharan Africa, as well as some key countries in the Middle East: Afghanistan, Iraq, and Yemen are all projected to at least double in population over the next 40 years, tilting the playing field uphill for ongoing development and stability efforts.

For Africa, the estimates should be a wake-up call, argue Malcom Potts and Martha Campbell on Foreign Policy:

Rapid population growth is bad news for the continent, as it will likely outstrip gains in economic development. It’s also a wake-up call: If the world doesn’t begin investing far more seriously in family planning, much of our progress fighting poverty in sub-Saharan Africa over the last half-century could be lost.

Investment in Family Planning Determines Growth Rate

Worse, both Potts/Campbell and Madsen warn that even with the current revisions, estimates may still be low. “It would be a mistake to focus only on the medium UN projection of 9.3 billion people by 2050 as most commentators do,” write Potts and Campbell:

The high projection would take us to 10.6 billion in 2050. The low projection would mean 8.1 billion. (Just for a sense of scale: The difference between these high and low variants is equivalent to the entire global population in 1950.)

And Madsen singles out Nigeria once again:

Nigeria’s fertility rate, measured at almost six children per woman in 2008, is projected to fall to slightly over three children by 2050. This is highly unlikely if current trends continue, because only 10 percent of married women in Nigeria use effective contraception, while 20 percent want to avoid pregnancy but aren’t using family planning services.

The New York Times’ Justin Gillis and Celia W. Dugger also highlighted the role of family planning:

Though [family planning programs] were a major focus of development policy in the 1970s and 1980s, such programs have stagnated in many countries, caught up in ideological battles over abortion, sex education, and the role of women in society.
…
Over the past decade, foreign aid to pay for contraceptives – $238 million in 2009 – has barely budged, according to United Nations estimates. The United States has long been the biggest donor, but the budget compromise in Congress last month cut international family planning programs by five percent.

In Uganda, where the population growth rate is the third highest in the world (after Yemen and Niger), the Daily Monitor reported that the unmet need for family planning is 41 percent. “Our reproductive health and family planning services remain mainly urban-based yet the majority of our women are in rural areas, some of them quite remote where accessibility remains poor,” the country’s State Minister for Planning, Fred Omach, told the Monitor.

“Every billion more people makes life more difficult for everybody – it’s as simple as that,” John Bongaarts of the Population Council told The New York Times. “Is it the end of the world? No. Can we feed 10 billion people? Probably. But we obviously would be better off with a smaller population.”

For more on the latest UN population projections, be sure to check out The New York Times’ “Room for Debate” feature on the topic, with input from Jamais Cascio, Joel E. Cohen (see his New Security Beat appearances as well), Warren Sanderson, David E. Bloom, Jason Clay, and Brad Allenby.

Sources: Sources: Daily Monitor, Foreign Policy, Grist, National Population Commission (Nigeria), The New York Times, Population Reference Bureau, UN Population Division.

Chart Credit: Arranged by Schuyler Null, data from UN Population Division, World Population Prospects, 2010 Revision.