Where populations are booming and shrinking

Families have been shrinking and population growth has been slowing in most nations over the past several decades, according to World Bank data.

Why it matters: Labor shortages, strained elderly care systems and slowed economic growth could all follow if birth rates remain below replacement levels for a long period of time, demographers warn.

Populations change slowly, humans are living longer and many rich countries still attract lots of immigrants. So despite almost half of countries around the world having birth rates below the level needed to replace current generations, most of those populations are still growing.

• Even with decades of a one-child policy and little immigration, China's population is still managing to grow. That is expected to end in 2026, according to U.S. Census Bureau projections.

Yes but: We're already starting to see impacts. Hungary, Italy, Portugal, Japan, Ukraine and 17 other nations are already watching their populations decline, according to the 2017 data.

• Low birth rates have been a factor in the state of Europe's economy, Richard Cincotta, director of the Global Political Demography Program at the Stimson Center, told Axios.
• Japan is struggling with a critical labor shortage, forcing them to accept more foreign workers.
• Governments in Japan, Germany, Singapore and other nations have rolled out policies that incentivize having more babies.

What to watch: Immigration could become increasingly important to boosting low fertility nations' populations and sustaining GDP growth. These immigrants could come from places like Niger, Nigeria, Democratic Republic of the Congo and other nations with booming populations. Much would depend on the willingness of governments and communities to welcome more foreigners into their workforces and societies.

On the other hand, with new, emerging technologies, "future economies will probably not need as many workers as they once did," Cincotta said.

• A future, smaller workforce could lead to higher wages, Global Aging Institute president Richard Jackson said, but taxes would also likely rise to help cover the costs of caring for larger retired generations living longer than ever.
• And some aging economies with highly skilled workforces, such as in South Korea (which has a very small population of immigrants) and Germany, are doing just fine so far.

The bottom line: Just before the fertility rates plummeted in the '70s, there was spreading concern for overpopulation. Demographic shifts are slow, and the downward trend we're seeing now could still reverse itself, but "each year that goes by with new data showing no rise — or even a decline, as we saw this year — makes a more fundamental shift more likely," Jackson said.

Go deeper:

• Special report: The aging, childless future
• People around the world are waiting longer to have kids
• The new rite of passage: Young, busy and still single