U.S. to remain third most-populous country

The United States is expected to remain the third most-populous country in the world through 2050, ranked behind China and India, while India's population is projected to exceed China's by 2025, according to a report released Monday by the U.S. Census Bureau.

Countries expected to advance in the population rankings have high fertility rates, such as Ethiopia and Nigeria, while those with low fertility rates are expected to drop, such as Russia and Japan, currently ranked ninth and 10th, respectively, in 2011 population rankings, the bureau reported.

Ethiopia was expected to vault up the rankings, from 13th to seventh by 2050, tripling in population from 91 million to 278 million.

Similarly, Nigeria was expected to more than double its population by 2050 -- from 166 million in 2011 to 402 million -- propelling that country from seventh place in 2011 to fifth by 2025 and fourth by 2050, the bureau projected.

But the bureau cited "persistent low fertility rates" for Russia and Japan, predicting those countries would drop off the top 10 list by 2025.

Those projections did not surprise William Frey, a demographer and senior fellow at the Brookings Institution in Washington, D.C. The United States' steady position, Frey said, "shows we have a continuing healthy population growth in this country when many other developed countries around the world are going to be growing modestly or declining."

Frey attributed the strong U.S. population growth to "immigration, which helps fertility along. Immigrants bring in young people, which helps to increase our fertility levels, and also fosters much more interaction across the world in a global economy. I think the message for the U.S. is it's going to be a global player for a quite a long time [with] a much more youthful and energetic population than a lot of our European competitors."

Frey said the bureau's projection that India will have more people than China by 2025 wasn't surprising either, because of its higher fertility rate than China, which has long imposed a one-child policy. He surmised that China's population will "age rapidly," having an adverse impact on its labor force.

Japan's projected drop off the top 10 most populous countries list, Frey added, is the result of the "long-term impact of low fertility and low immigration," which also means an "aging population. "Clearly, they'll probably make some changes between now and then [2025]," Frey said of Japan. "But it shows you the situation you can put yourself in if you keep your borders closed."

The Census Bureau International Data Base, which studied 228 countries and areas, has been conducting estimates and projections for individual countries for more than 50 years, Loraine West, a demographer in the bureau's population division, said in a statement.