• Elon Musk argued for higher birth rates again, saying otherwise we will all "end up in adult diapers."

• He claimed without evidence that the environment can support it "even if we doubled the size" of the global population.

• Experts have stated other factors causing birth rates to decline.

Elon Musk argued on Monday that it's "total nonsense" that people were not having have kids because it was bad for the environment, and made another plug for people to have more children to prevent the collapse of civilization.

"Some people think that having fewer kids is better for the environment. It's total nonsense. The environment is going to be fine, the environment is going to be fine even if we doubled the size of the humans," the Tesla CEO told the closed-door All-In Summit via video call on Monday.

"At least maintain our numbers," he said. "We don't necessarily need to grow dramatically, but least let's not gradually dwindle away until civilization ends with all of us in adult diapers, in a whimper."

Musk did not provide evidence to back up his claims. Swedish researchers in 2017 found that having one fewer child per family could reduce carbon emissions by about 58.6 metric tons each year in developed countries, CNBC reported. However, other experts said that a change in lifestyle and a compounding change in pro-climate policies could have a greater impact on the environment than not having children, Vox reported.

Musk also claimed that if people didn't have kids, humankind would collapse upon itself.

Musk has previously voiced his concerns about global birth rates. In December, he warned that "civilization is going to crumble" if people don't have enough children. He furthered that argument last week by claiming that Japan could "cease to exist" because its birth rate was declining.

While birth rates in some countries are indeed falling, the 2019 UN World Population Prospects report, the most recent edition, estimated that the global population could reach 9.7 billion in 2050, from 7.7 billion in 2019.