The piece, written by Fred Pearce points to Japan as a case study for what could go wrong in the relatively near future.

"The world's population is accelerating towards collapse, but few seem to notice or care," Tesla 's CEO tweeted to his nearly 10 million followers. He pointed to a November article in New Scientist magazine titled, " The world in 2076: The population bomb has imploded ."

Elon Musk usually tweets about mundane topics, from LA traffic to Tesla projects. On Thursday he was more dire.

Rather than a meltdown where the Earth's population outstrips the planet's ability to feed everyone, we could be headed toward a more subtle but equally disastrous outcome where our population simply does not replace itself fast enough.

"The world has hit peak child," the late Hans Rosling, a professor at the Karolinska Institute in Stockholm, said in the article.

Indeed, Japan's fertility rate is 1.4 children per woman, well below what is required to sustain population growth.

While Japan is perhaps the most well-known example of a country's population aging, the article in the London-based magazine also points to Germany and Italy, both of which "could see their populations halve within the next 60 years."

The article spells out some of the problems an older population might bring, including less innovation, cultural shifts and worse and more recession-prone economies.

According to the U.S. Census Bureau, the nation's population is roughly 325 million with a net gain of one person every 12 seconds.

However, Pearce does point out some silver linings. "Old could be the new young," he writes, adding older societies are less likely to start wars. And, he points out, fewer people on the planet would give Earth's ecosystem a breather:

"Nature, at least, would enjoy the silver lining."

The so-called population bomb has been speculated about for nearly half a century, dating back to at least 1968 when two Stanford University researchers published a book titled "The Population Bomb" that predicted mass starvation in the 1970s and '80s due to overpopulation.

Musk has been known to pontificate on theories outside the mainstream, including famously last June when he said there is only a "one in billions" chance we're not living in a computer simulation.