The UN expects the global population to peak around 2100, but other experts – and Musk – believe that is far too optimistic. One startling scenario predicts the top to be in 2064.
A projection from the University of Washington’s Institute for Health Metrics and Evaluation (IHME) warned that 23 countries, including Japan, Spain, South Korea and Thailand, will see their populations more than halve by the end of the century. China is currently the most populated country in the world but its numbers are forecast to crash from a peak of 1.4bn to 732m in 2100.
In developed countries, longer life spans and falling fertility rates mean societies are ageing rapidly with many soon unable to maintain their populations as deaths outstrip births. Rising numbers of women in education and work, usage of contraception and often precarious financial health of younger generations have driven the sharp decline in fertility rates in recent decades.
In China, enforced lower births via the one-child policy between 1980 and 2015 means its population is now ageing rapidly. Analysts at Bank of America warn it could begin declining as soon as this year after a 12pc drop in births in 2021 came off the back of an 18pc plunge the previous year.
Britain escapes relatively lightly in the IHME projections, seeing its population rise slightly by 2100 after a peak in 2063. But it still faces the same challenges from a rapidly ageing population – a boy born in the UK in 2020 can expect to live until 87 years old, and a girl over 90.
The UK’s fertility rate has fallen to 1.6 births per woman, but remains above Spain’s at 1.2, Japan’s at 1.4 and Germany’s at 1.5.
Lord Willetts, former minister and president of the Resolution Foundation, says: “Compared with Italy, or Japan, or China, our adjustment is not as severe. Britain is up there, almost as good as America, in that our birth rate remains closer to 2.
“What we’ve got at the moment is a very severe fall in the birth rate, partly because of the pandemic. So, looking ahead, it looks as if in the long run [Britain is] moving down to a birth rate rather lower than we are familiar with.”
However, the Office for National Statistics warned last week that the UK’s natural population will begin falling as soon as 2025, meaning births are not keeping up with deaths. That is almost two decades sooner than previously thought, though immigration will prop up the population until 2058 before an overall decline begins.
The economics of the crisis poses huge challenges for governments. Without policy action, an older society sucks more money for health and social care spending and pension payments.
More retirees become a bigger burden on a relatively smaller workforce, meaning taxes may need to be pushed up further to maintain the same level of services. Britain also has less specialist and old age-friendly housing compared to other countries, such as the US and New Zealand.
In the UK, soaring health spending from ageing, rather than higher pension costs, will pose the biggest pressure on the public finances.
Total age-related spending will rise from 21pc of GDP in 2022-23, to 29pc in 2067-68, according to the Office for Budget Responsibility. In the late 2060s, spending on state pensions will be 7pc of GDP but spending on health will soar from today’s 8pc to 14pc while social care costs will rise from 1pc to 2pc.
Ben Zaranko, economist at the Institute for Fiscal Studies, says a declining population is not necessarily a problem for the economy but the ageing alongside it poses challenges.
“If you’ve got a smaller population, you have a smaller economy, but each individual might be just as prosperous. The problem is it’s coming alongside a change in the structure.”
He adds that this could mean a greater focus on GDP per capita as population declines mean productivity needs to pick up to maintain or grow the size of the economy.
“As economies get richer, each individual tends to have fewer children on average and so we shouldn’t be decrying the fact that we’re a more prosperous society. It is going to create challenges but a lot of the underlying causes here are things to celebrate.”
