The United Nations projects that India will overtake China as the world's most populous country by 2030, five years earlier than expected.
A new report says the world's population is expected to climb to nine-point-one billion by 2050 -- a 40 percent increase over current figures.
Virtually all of the growth is expected in developing countries, some of whose populations will triple. Little or no population growth is expected in industrialized countries.
A U-N summary cautions that population growth will depend on the impact of the HIV/AIDS virus, and how well developing countries implement birth-control and fertility programs.
Between 2005 and 2050, eight countries will contribute half of the world's population increase. The populations of Afghanistan, Burkina Faso, Burundi, Chad, Congo, the Democratic Republic of Congo, East Timor, Guinea-Bissau, Liberia, Mali, Niger and Uganda are expected to triple.