USA Today reports on a study by the Population Reference Bureau (PDF format): "Many of the world’s largest industrialized nations will lose population between now and 2050 as low birth rates, struggling economies and curbs on immigration stifle growth, says the author of a world population report.
The annual study by the private Population Reference Bureau found that, while the world’s population will increase nearly 50% by mid-century, Japan will lose 20% of its population in the next 45 years, while Russia, Germany and Italy will also see declines." If the current trends continue, Russia’s population will decline by 17%, or 25 million people. Bulgaria will decline by 38%. With the exception of the United States, which is expected to grow by 43 percent to 420 million people, other western developed countries will register population declines. Developing countries will grow about 14 times as fast as industrialized countries between now and 2050.

And India, the study claims, will overtake China by 2050 as the world’s most populous nation.