STEVE INSKEEP, HOST:
We have some news about the year that just ended. The world's population grew by more than 75 million people last year.
MICHEL MARTIN, HOST:
Now, that sounds like a lot, but the pace of growth is slowing.
RACHEL FRANKLIN: We know that the global population is likely to even out in the coming decades and then potentially even to start to decline.
INSKEEP: Rachel Franklin at Newcastle University in England studies trends among the 8 billion people now sharing this planet. She sees hints of our future in a country that has an aging population and a declining birthrate.
FRANKLIN: What's happening in Japan is what's going to happen in lots of countries around the world in the coming decades. At least for a few decades, we'll have a lot of older people supported by sort of a narrower foundation of those who are in the labor force.
MARTIN: As countries become more prosperous, their birthrates tend to drop.
FRANKLIN: Many countries already produce fewer than the 2.1 babies that we generally say are required in order to maintain a population size.
INSKEEP: Now, in theory, a smaller population could be easier to manage. Fewer people might consume fewer resources and contribute less to climate change. But we can't really count on slower population growth to take care of that problem.
FRANKLIN: So we could have fewer people in the world. But if their living standards increase at the pace that our living standards did for the past 100 years, we're still going to see a huge environmental impact.
MARTIN: William Frey is a demographer at the Brookings Institution. That's a think tank. He says that in the U.S., immigration will determine future population trends.
WILLIAM FREY: Just from a demographic standpoint, this country is very much dependent on immigration in the future to have sustainable growth.
INSKEEP: So in a time of declining birthrates, it matters a lot where people prefer to move.
FRANKLIN: It's hard to know what fertility preferences may look like in a couple of decades. We don't know if younger generations may prefer to move more, and we don't know if we'll decide to increase the numbers of people that we admit into this country.
MARTIN: And for this new year that is just getting started, the U.S. population is expected to grow by one person about every 24 seconds. That is taking into account births, deaths and international migration.
(SOUNDBITE OF GEORGIA ANNE MULDROW'S "BROKENFOLKS") Transcript provided by NPR, Copyright NPR.
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