Elon Musk, founder of Tesla and SpaceX, steps on to the stage at a conference in Italy. In three decades, the world's population will be "one-tenth of its current size," he tells the audience. The birth rate, he adds, "is maybe half the replacement rateThe rate of births needed for babies to replace their parents. ". At one point the conference host suggests the crisis is still 50 to 60 years away. "I think it's even sooner than that," Musk replies.¹

Many people disagree. The global birth rate is above the replacement rate and the global population is set to rise over the next few decades. Nonetheless, across Europe, America and Eastern Asia, fertility rates are falling at record levels.

The fertility rate is the average number of babies born to each woman. In England and Wales that number has reached 1.44 - the lowest rate since 1938. Meanwhile, in Scotland, that number has reached 1.3.²

For a population to stay the same, the fertility rate needs 2.1 babies per woman. However, in several countries around the world, it is barely half this figure. For example, in Japan the rate is 1.21, in Taiwan 0.865 and in South Korea just 0.72.³

That said, economistsExperts in economics, the branch of knowledge concerned with the production, consumption and transfer of wealth. disagree about whether this is a problem. Some argue that, if the population declines, the number of people paying taxes will also shrink. This means governments will struggle to pay for basic services - just as the population ages and the stress on the health service increases.

One solution is immigration, which keeps the population growing. This often means taking the most talented people from other countries, even if these countries are experiencing their own population decline. And, as journalist Annabel Denham warns, the levels of immigration that may be needed in the future could cause "social unrest".⁴

But others argue that there is no problem here: either because the population is still growing, or else because a shrinking population is a good thing. According to UN projections, the global population is likely to peak at 10.3 billion in the next 60 years. Population growth in Africa, Central and Southern Asia will offset any decline in Europe and America.⁵

Even if these figures are wrong, a decline in the global population might have long-term benefits. By reducing the demand for food and energy, it will slow the pace of global warming and environmental destruction. Fewer babies could be good for the planet.

A shrinking population also brings opportunities. Not having a family gives people - especially women - more freedom to pursue their own lives. AI, automation and bringing older people back into employment could make up for a smaller workforce.

So Elon Musk is probably wrong to say that "it should be considered a national emergency to have kids".⁶ Yet, even if the Earth is not running out of humans, declining populations also mean the loss of languages, cultures and communities. When couples have children, it suggests they are hopeful about the future. Right now, too many people feel the opposite.

Is Planet Earth running out of humans?

Yes: Fertility rates are falling across America, Europe and Eastern Asia. Most government interventions do nothing to slow the trend. Musk is right to warn about the coming crisis.

No: Globally, the population is growing and expected to peak in the second half of the century. Immigration, AI and automation can solve shortages in the workforce.

Or... The global population may be growing, but declining birth rates in many developed countries suggest that people no longer feel the security, stability or hope needed to start a family.