The ‘youthquake’ of Africa will look like this, the UN projects. The continent’s 54 countries are expected to host 2.9 billion people by 2050, a 70 per cent jump from today. By mid-century, Africans will comprise 30 per cent of humanity, up from 8 per cent in 1950 and 21 per cent now.

The other explanation for the surge of Africans as a percentage of global population snapshots is the desire for children is plunging elsewhere. About two-thirds of the world’s eight billion people live in countries where the fertility rate is below the replacement threshold of 2.1 births per woman. The UN predicts 61 countries to shrivel population-wise by at least 1 per cent by 2050. These countries will be mainly ones that are rich, in Eastern Europe and East Asia. The OECD says only Israel of its 38 members has a fertility rate above the replacement rate – average member fertility has plunged from 3.3 in 1960 to just 1.5 in 2022. South Korea, where dog strollers now outnumber baby prams, has the world’s lowest fertility rate at 0.72. The rate is forecast to drop further and cause the population to contract 30 per cent.

Prominent countries already shrinking are Hungary (since 1981), Russia (from 1992), Japan (since 2010), Italy (from 2014), and China (since 2021). But for immigration many Anglo countries such as Australia, which had a record-low fertility rate of just 1.5 in 2023, would be dwindling too – why Treasurer Jim Chalmers in May urged Australians to have more babies. Another way to look at the problem is that the number of children in Japan, where the fertility rate is 1.2, has declined for the past 43 years – children now only comprise a record low 11.3 per cent of Japanese.

Many demographers reckon global bodies are underestimating the population decline and the automatic aging of societies. They say global bodies fail to see that the economic and social forces reducing the desire to procreate in advanced countries are now universal. These factors include expectations of low infant mortality, enhanced female education, better career prospects for women, long working hours, changing social mores, and urbanisation. The stance, though, of no kids to protect the climate seems just a Western fad.

The problem for the world is the economic, diplomatic, investment, political and social consequences of dropping populations are likely to be substantial and grim. Declining populations are a bigger economic challenge than ageing populations because they herald a permanent drop in the demand that drives economies. Fewer births reduce society’s most dynamic force; parents seeking better lives for their children. Businesses will invest less if fewer people are consuming less. Housing construction will decline if fewer people need homes. Such outcomes hint at deflation, sluggish economies and poor investment returns.

Government finances face difficulties as populations shrink and age because a smaller working-age cohort must support more elderly. A stretched number of fewer workers could hobble innovation and productivity. At the same time, labour shortages could boost wages, thus inflation and interest rates.

Politics will face novel challenges as nations imagine themselves shrivelling into ruin.

Such gloom fuels the grievance politics that rabble-rousers can exploit. Note how populism is rife in depopulating parts of Europe and pronounced in countries such as the US where a long-dominant ethnic group is sliding into minority. Another political tussle will be intergenerational if the aged dominate issues such as tax and government debt and vote for outcomes that burden the young. Shrinking countries population-wise are likely to shed their global (military) power. Any rejigging of the world order rarely happens without friction.

Politicians, sensing the dangers, are grasping to solve a problem that self-perpetuates. Policymakers are toying with affordable childcare, baby payments, cheaper housing to encourage bigger families, child tax breaks, flexible working conditions to help parents work, free fertility checks, loans to newlyweds with repayments foregone on the third child (Hungary 2019), longer parental leave, public-education campaigns, and even government-run events and dating apps for singles.

No solutions have worked, not even China’s ending of the one-child policy of 1979 to 2015 – Beijing now encourages families of three children. Nor likely to prove effective is President Xi Jinping’s appeal last October for woman to freeze careers for child-rearing (to ‘create a new trend of family’). Nor French President Emmanuel Macron’s call in March for French ‘demographic rearmament’. Nor seen promising is South Korea’s idea of a US$70,000 baby bonus, double annual per-capita income, to reverse its fertility crisis.

The failure to boost fertility rates has forced advanced countries to turn to immigration as a solution. But this workaround often countermands pro-children policies because migrants suppress wages, erode work conditions, boost housing costs, strain health services, and come with assimilation issues. Greece’s solution implemented this year to overcome labour shortages caused by emigration on top of a low birth rate was to adopt a six-day working week in some industries.

The biggest threat of today’s voluntary mass-depopulation – the first one not caused by despots, disease, natural disasters, or wars – is its unprecedented nature forms a shock. Capitalist societies are geared for growing populations, as happened over the 19th and 20th centuries when the world’s population increased eight-fold from one billion in 1800. Over the past 200 years, societies became designed to accommodate more people, a trend that encourages optimism and dynamism.

Much might need to adjust as fewer people means less of everything. Policymakers could no longer assume positive economic growth. Companies could no longer reflexively plan to expand. Town planning might be about shrinking social infrastructure. And so on. In 1937, when the Great Depression had slowed population growth, UK economist John Maynard Keynes foresaw that ‘a declining population may be very disastrous’. Too true most likely. The ‘population bust’ looms as a primary challenge of the 21st Century.

At an aggregate level, to be clear, the world’s population is forecast to peak at 10.4 billion in the 2080s. But that’s mainly due to Africans reproducing and won’t overturn the consequences of falling populations elsewhere. A note of caution is that demographic projections largely extend trends that could change. A rising population is no guarantee of prosperity. Declining populations could come with benefits such as less environmental damage, fewer clashes over resources and reduced inequality if labour shortages boost wages.

Such musings reinforce how much is speculation when it comes to analysing a sustained decline in populations because it’s new. The novelty only intensifies the uncertainty of what consequences a depopulating world-ex Africa might unleash.