UNITED NATIONS -- Earth's human population is expected to coast upward to 9.6 billion by 2050 and 10.9 billion by 2100, up from 7.2 billion people alive today, a United Nations agency has projected.

The U.N. Department of Economic and Social Affairs yesterday released revised numbers for the coming century, raising median estimates for population growth in 2050 and 2100. The agency's prior best guess had humanity at 9.3 billion in 2050 and 10.1 billion in 2100.

Most of this growth will take place in less-developed, lower-income nations, mostly in sub-Saharan Africa. John Wilmoth, director of the population division at DESA, explained that the revisions reflect adjustments to how high-fertility countries are behaving.

In countries like Nigeria, Uganda, the Democratic Republic of the Congo and Afghanistan, women are still averaging more than 5 children per family, while many high-income nations in Western Europe and elsewhere are having fewer than 2 children per woman.

Developing regions are today home to about 5.9 billion, but that number is expected to soar to 8.2 billion in 2050. Population in developed nations will stay about the same, at 1.3 billion.

Wilmoth stressed that such projections are tricky when researchers start looking past the next few decades. DESA came up with the 10.9 billion figure as a median between extreme estimates of 6.8 billion people alive in 2100 to as many as 16.6 billion.

"We really don't know what these trends will be after a period of several decades," he said during a U.N. press conference on the population survey, explaining that the estimates reflect a best guess based on the future resembling the past.

Much of the uncertainty has to do with births and whether citizens of lower-income nations will start to change their ways and have fewer children if and when the standard of living in those countries improves. Wilmoth noted that fertility rates in India and Indonesia, to cite two instances, have recently dropped, because governments there have aggressively pursued family planning policies to rein in big families.

Efforts needed to avoid two extremes

Wilmoth said low fertility could be viewed as just as difficult a challenge as high birth rates because governments have to deal with rapidly aging populations and fewer children to replace them. He cited Japan as one nation currently coping with this threat.

"The main story is to avoid the extremes of either rapid growth due to high fertility or rapid decline due to low fertility," he said.

Wilmoth also appeared to argue that humanity would adapt to either reality. He said the world population doubled from 1960 to 2000, and the pace of food production more than doubled in the same period, so he expects Earth to adjust unless the planet hits either extreme.

As for the United States, DESA considers fertility here to be on the low end, but just barely. U.S. families are averaging about 2 children per woman, which is just under the 2.1 children per woman needed to replace aging adults, Wilmoth said.

Immigration is expected to help keep the United States stocked with young people. DESA anticipates continued immigration to the United States at about the same level as today out to 2050 and 2100.

Another trend noted by the report is the emergence of more large countries. India and China will be the most populated throughout the century, with India expected to surpass China around 2028, when both will be home to about 1.45 billion. And Nigeria is expected to pass the United States by midcentury and could contest China and India as the most crowded country on the planet by 2100.

In Europe, meanwhile, fertility is below the level required to replace its population, but DESA did see an increase ahead, from 1.5 children per woman in 2010 to 1.8 by 2050 and 1.9 by 2100.

Another factor affecting the whole picture is age expectancy. DESA said life expectancy worldwide from 2005 to 2010 was 69 years, but that number will climb to an average of 76 years by 2050 and 82 years by 2100.

"By the end of the century, people in developed countries could live on average around 89 years, compared to about 81 years in developing regions," the report said.

Reprinted from Climatewire with permission from Environment & Energy Publishing, LLC. www.eenews.net, 202-628-6500