The world's population will increase by 40 percent to 9.1 billion in 2050, but virtually all the growth will be in the developing world, especially in the 50 poorest countries, the U.N. Population Division (search) said.
In a report Thursday, the division said the population in less developed countries is expected to swell from 5.3 billion today to 7.8 billion in 2050. By contrast, the population of richer developed countries will remain mostly unchanged, at 1.2 billion.
"It is going to be a strain on the world," said Hania Zlotnik, the division's new director. She said the expected growth will be concentrated in countries that already struggle to provide adequate shelter, health care (search) and education.
The report reconfirmed many trends, including an increasingly aging population in developed countries. But it said immigration would prevent the overall population in richer countries from declining.
The United States is projected to be the major net recipient of international migrants, 1.1 million annually, with its population increasing from 298 million in 2005 to 394 million in 2050, the report said.
Between 2005 and 2050, population growth in eight countries — India, Pakistan (search), Nigeria, Congo, Bangladesh, Uganda, the United States, Ethiopia and China — is likely to make up half the world's increase, the report said.
Median fertility is expected to decline from 2.6 children per woman today to slightly over 2 children per woman in 2050.
Zlotnik said India's population will surpass China's in the coming decades because its fertility, currently at 3 children per woman, is higher than China's, estimated at 1.7 children per woman.
In 2000-2005, fertility levels remained above 5 children per woman in 35 of the 148 developing countries, including 30 of the poorest nations. The pace of decline in several countries in sub-Saharan Africa and south Asia was slower than anticipated.
In southern Africa, the region with the highest AIDS prevalence, life expectancy has fallen from 62 years in 1995 to 48 years in 2000-2005, and is projected to decrease further to 43 years over the next decade before a slow recovery starts, it said.
Thoraya Obaid, executive director of the U.N. Population Fund (search), said the new projections should spur more action to stop the spread of HIV/AIDS and help couples freely determine the size of their families.
"We must take more urgent action to promote access to reproductive health, including family planning, and fight HIV/AIDS to save millions of lives from AIDS and maternal death, as well as to reduce poverty in developing countries," she said in a statement.
In 2002 the Population Division had estimated global population in 2050 of 8.9 billion.