Elon Musk, the world’s richest man and Tesla CEO, warned that the nation of Japan will eventually “cease to exist.”

Musk, who has repeatedly spoken out about the dangers of population collapse, was responding to an article about population decline in Japan in 2021. The decline marked a drop of 644,000 to 125.5 million in the span of 12 months.

“At risk of stating the obvious, unless something changes to cause the birth rate to exceed the death rate, Japan will eventually cease to exist. This would be a great loss for the world,” Musk tweeted.

At risk of stating the obvious, unless something changes to cause the birth rate to exceed the death rate, Japan will eventually cease to exist. This would be a great loss for the world.

— Elon Musk (@elonmusk) May 7, 2022

It wouldn’t be the first time Musk has spoken out about the topic of population collapse. In January, the SpaceX founder said that the world should be “much more worried about population collapse” and slammed the United Nation’s projections on population growth.

According to the United Nations, the world will continue to see an upward trend in population growth over the next 80 years, with some developing countries exceeding over a billion in population.

“UN projections are utter nonsense,” wrote Musk. “Just multiply last year’s births by life expectancy. Given downward trend in birth rate, that is best case unless reversed. If there aren’t enough people for Earth, then there definitely won’t be enough for Mars.”

UN projections are utter nonsense. Just multiply last year’s births by life expectancy. Given downward trend in birth rate, that is best case unless reversed.

— Elon Musk (@elonmusk) January 18, 2022

In the same thread, Musk linked to several articles published by NPR and BBC, noting the alarming drop in world births. In one of the articles, as reported by NPR, the U.S. birth rate fell by 4% in 2020.

The drop occurred for the sixth year in a row.

“If the alarming collapse in birth rate continues, civilization will indeed die with a whimper in adult diapers,” Musk warned in a separate tweet.

In March, Musk responded to a YouTube video identifying Russia’s invasion of Ukraine, in which he singled out Russia’s low birth rate as a “foundational issue.”

He asked: “After all, what good is land with no people?”

Last year, Musk called birth rate collapse the “biggest threat to human civilization” in response to an infographic posted by Simon Kuestenmacher.

“Elegant way of showing global fertility data for every country in 2019. It’s actually a rather elegant visual. Spend a few minutes studying it and might become as big as a fan of the piece as I am,” Kuestenmacher said.

Birth rate collapse is the biggest threat to human civilization

— Elon Musk (@elonmusk) September 22, 2021