Science
AP
Elon Musk made a grim prediction on Twitter on Thursday."The world's population is accelerating towards collapse, but few seem to notice or care," the Tesla CEO wrote.
Musk was responding to a New Scientist article entitled "The world in 2076: The population bomb has imploded," which forecasted the gradual decline of the world population over the next 60 years.
Though the global population is currently rising - mostly due to high fertility rates in African countries - experts have also observed falling fertility rates around the world.
This is concerning for demographers and economists because countries must hit what's known as "replacement fertility" in order to keep their populations - and their economies - stable. Replacement fertility is around 2.1 children per woman.
If countries don't have enough babies, they won't produce a strong enough labor force to match the economic output of the older generations. And in the most extreme cases, low fertility rates create a vicious cycle of low spending and low reproduction. People who can't afford to have kids don't bolster the economy, which leads people to have even fewer children.
Many of the world's wealthiest countries may not be far away from economic decline due to low fertility. The US, Denmark, China, and Singapore all have low fertility rates: 1.87, 1.73, 1.6, and 0.81, respectively. Japan, one of the most extreme cases of population implosion, has a fertility rate of 1.41. Its population has been declining for the past few years.
A 2016 UBS report predicted Japan's population crisis could spread to other industrialized countries over the next 20 years, based on the finding that many of today's wealthy countries bear a striking resemblance to 1990s Japan.
The data don't necessarily support Musk's claim that the world is accelerating toward "collapse," however. The United Nations, for instance, still predicts the global population will reach 9.7 billion by 2050 and 11.2 billion by 2100.
In addition, analyses from Our World in Data show the global fertility rates tending toward just under two children per woman by 2100. But there have been cases when fertility declined rapidly. China, for example, went from above six children per woman to under three in a span of just 11 years between 1967-1978. The United Kingdom, meanwhile, took 95 years from 1815 to 1910.
The extent to which humanity is headed for "collapse" may depend on whether fertility rates decline rapidly like they did in China in the 1970s or gradually like the UK in the 1800s.