The booming population growth of the past century has slowed, but improving health conditions and stubbornly high birth rates in many developing countries continue to swell the world's population by some 80 million people every year.
Yet, according to the 2010 World Population Data Sheet, richer nations face a dwindling workforce that will be less able to support their growing elderly populations. Meantime, in many poorer countries, populations are younger and growing rapidly - exacerbating poverty and threatening the environment.
In 2010, the global population reached 6.9 billion, with nearly all the growth in the world's developing countries. According to the report, the world's poorest developing countries account for 20 million of the 80 million people being added to the global population every year.
Carl Haub, senior demographer with the Population Reference Bureau and lead author of the Data Sheet, says by 2050, population growth in Africa alone will boost world numbers by one billion, assuming that birth rates today are declining on that continent and continue to do so.
Asia is expected to add the most people, about 1.3 billion, by 2050.
"In many cases now, it's becoming more and more evident that simply is not happening."
Demographers predict that birth rates in developing countries will eventually decline following the trend in industrialized nations.
Yet, as the Data Sheet documents, Asia is expected to add the most people, about 1.3 billion, by 2050. That is likely to impose greater burdens on governments to meet the health, education and economic needs of large and young populations.
In the developed world, the numbers tell a very different story. Chronically low birthrates have created a shrinking pool of work-age people to support the wealthier countries' elderly populations.
Haub gives a stark example, comparing Ethiopia and Germany.
Both have roughly the same number of citizens, but the similarity ends there. Ethiopia is expected to double its population from 85 million to 174 million by 2050. The population in Germany will likely decline from 82 million to 72 million over the same period.
Europe is the first region of the world to see a long-term decline in fertility.
Haub says, with its much lower birth rate, Germany faces escalating problems resulting from a smaller adult workforce.
"And you can see that Germany already has only three people of working age for one person of the retirement ages. So they have an immediate and growing crisis in their pension and health care system and they know it, for sure."
Implications for retirement and health care
According to the report, Europe is the first region of the world to see this long-term decline in fertility.
Currently, there are about four working age people for each person over 65. That number is expected to drop to 2-to-1 by 2050.
Japan and South Korea are facing similar problems, says James Gribble, vice president of International Programs for the Population Reference Bureau. "[That] has implications for retirement and health care for the elderly and the need to have a sufficient number of children moving into the labor force as they become adults."
In the United States, the number of people 65 and older is expected to more than double from 40 million today to 89 million by 2050.
Passengers wait for trains in the United States, where immigrants can help bolster the working age population.
Role of immigrants
And the total U.S. population could grow from today's 310 million to more than 420 million, depending on migration trends, says Linda Jacobsen, vice president of Domestic Programs for the Population Reference Bureau.
"Immigrants can help to offset the decline in the elderly support ratio. They can help bolster the working age population and improve the potential solvency of Social Security, just as an example," says Jacobsen. "I don't know that I would suggest that it is the solution. It's not the solution, but it certainly has played an important role in keeping the U.S. population not looking like those in Japan and some of the countries in Western Europe."
The 2010 World Population Data Sheet presents detailed information on more than 200 countries. It's based on country sources, demographic surveys and studies from state and international agencies. Population Reference
Bureau President Bill Butz hopes the findings provide the public and policy makers with a clearer picture of the challenges population growth continues to pose to global health, the economy and the environment.