The United Nations has raised its optimistic "low" estimate of world population growth due to an increase in childbirths in some industrialized nations.
In a biennial report released last week, the U.N. Population Division increased slightly a projection it uses to forecast the size of the human population. The "low-variant" scenario of population growth now foresees 117 million more people on the planet in 2050 than it did two years ago.
While the "median-variant" scenario, often seen as "most likely," remains almost the same as before - predicting a world with 9.2 billion people by mid-century, up from nearly 6.8 billion today - the earlier low projection did not anticipate jumps in fertility in Europe and the United States [PDF].
U.N. demographers selected a high, medium, and low fertility rate in 2006 to estimate how many children would be born between the years 2005 and 2010. Three years later, the analysis concluded that the low fertility rate was too optimistic, according to Hania Zlotnik, director of the Population Division.
"[The difference] is tiny, but it affects how we think of the path over time. The more-developed regions are not losing population by 2050; they're maintaining their population size," Zlotnik said. "The high won't be as high and the low won't be as low just because of that change."
The revised projection has implications for the timing of the possible stabilization and reduction of world population, a target that is now pushed back a few years under the most hopeful of scenarios.
The United Nations expects nearly 8 billion people on Earth by 2050 in its low population estimate, according to the study [PDF].
The high projection, however, foresees some 10.5 billion people - a 295 million person decrease from the previous high projection. The medium projection is 9.2 billion people, about 41 million less than previously reported [PDF].
The revision in the low variant's total fertility rate - the average number of children per woman - was due to a rise in births in Europe and the United States following years of an "artificially depressed" fertility rate, according to demographics expert John Bongaarts. This lower rate was a consequence of large proportions of women delaying pregnancy until later in their lives.
"During the ‘90s, while the average age at childbearing was rising, women became more educated, wanted a job," said Bongaarts, vice president of the Population Council. "That artificial depression is now being removed as the average age of childbearing stops rising."
The 2008 U.N. revision projects that the industrialized world will average 1.64 children per woman between 2005 and 2010, up from an average as low as 1.35 projected in 2006.
"In the developed world, Europe and so on, fertility dropped well below two births per woman," Bongaarts said. "Very few people predicted fertility rates would increase. That has now happened."
The higher fertility rate will probably continue for some time, Bongaarts said, unless women decide to delay childbirth even further. Doing so would likely require an increase in the use of fertility drugs or another form of medical advance.
In the near future, however, families in wealthier countries may decide to prolong or reconsider having children due to the economic recession. "The little bit of an increase we've seen may peter out," said Carl Haub, senior demographer at the Population Reference Bureau.
But Haub said the observed increases in industrialized-world fertility rates will have a relatively minor effect overall - populations are expected to decline over time if average fertility rates remain below 2.1, which demographers consider the stabilization rate, absent net migration.
"Developed countries have largely painted themselves into a corner now," Haub said, referring to the likelihood that their low fertility will result in smaller populations in the years ahead. "All the growth will come from developing countries."
The 2008 U.N. revision also updated fertility rates for many developing countries. Rates for 2005-10 were generally lower in the recent assessment, with decreases in Africa (down 0.06 children per woman) and Latin America (down 0.11), although fertility jumped 0.44 in Oceania, a region that includes Micronesia and Polynesia. The fertility decreases generally explain the lower population projections for the medium and high estimates.
Population projections often rely on less-than-reliable data for the world's poorest countries, especially where violence or other conflict hampers research, Zlotnik said. "We have to guess. Sometimes we're more conservative, sometimes not," she said. "More often than not, we're more optimistic about the future and where the world is going."
Yet Zlotnik said that overall population growth "is inevitable." As a result, natural resources such as fossil fuels, timber, minerals, and water will likely be severely depleted in many regions. Population growth also compounds global challenges like climate change and biodiversity loss.
Feeding the world's expanding population will increase water demand 70 to 90 percent by 2050 without improved agricultural methods, according to the U.N. World Water Development Report. This is the case even though many regions are already reaching the limits of their water resources, said the report, which is being released at the start of this week's World Water Forum.
Photo credit: flickr/victoriapeckham, Creative Commons License.
The Earth was(according to our Ancestors)engineered for only 500,000 people.The Georgia Guidestones (reasource)