All over the world, countries are confronting population stagnation and a fertility bust, a dizzying reversal unmatched in recorded history that will make first-birthday parties a rarer sight than funerals, and empty homes a common eyesore.

Maternity wards are already shutting down in Italy. Ghost cities are appearing in northeastern China. Universities in South Korea cannot find enough students, and in Germany, hundreds of thousands of properties have been razed, with the land turned into parks.

Like an avalanche, the demographic forces — pushing toward more deaths than births — seem to be expanding and accelerating. Although some countries continue to see their populations grow, especially in Africa, fertility rates are falling nearly everywhere else. Demographers now predict that by the latter half of the century or possibly earlier, the global population will enter a sustained decline for the first time.

A planet with fewer people could ease pressure on resources, slow the destructive impact of climate change and reduce household burdens for women. But the census announcements this month from China and the United States, which showed the slowest rates of population growth in decades for both countries, also point to hard-to-fathom adjustments.

The strain of longer lives and low fertility, leading to fewer workers and more retirees, threatens to upend how societies are organized — around the notion that a surplus of young people will drive economies and help pay for the old. It may also require a reconceptualization of family and nation. Imagine entire regions where everyone is 70 or older. Imagine governments laying out huge bonuses for immigrants and mothers with lots of children. Imagine a gig economy filled with grandparents and Super Bowl ads promoting procreation.

“A paradigm shift is necessary,” said Frank Swiaczny, a German demographer who was the chief of population trends and analysis for the United Nations until last year. “Countries need to learn to live with and adapt to decline.”

The ramifications and responses have already begun to appear, especially in East Asia and Europe. From Hungary to China, from Sweden to Japan, governments are struggling to balance the demands of a swelling older cohort with the needs of young people whose most intimate decisions about childbearing are being shaped by factors both positive (more work opportunities for women) and negative (gender inequality and high living costs).

The 20th century presented a very different challenge. The global population saw its greatest increase in known history, from 1.6 billion in 1900 to 6 billion in 2000, as life spans lengthened and infant mortality declined. In some countries — representing about one-third of the world’s people — those growth dynamics are still in play. By the end of the century, Nigeria could surpass China in population; across sub-Saharan Africa, families are still having four or five children.

But nearly everywhere else, the era of high fertility is ending. As women have gained more access to education and contraception and as the anxieties associated with having children intensify, more parents are delaying pregnancy, and fewer babies are being born. Even in countries long associated with rapid growth, such as India and Mexico, birthrates are falling toward or are already below the replacement rate of 2.1 children per family….

The above comes from a May 24 story originally published in the New York Times.