SpaceX and Tesla CEO Elon Musk reiterated a theory on Friday that he's promoted in the past: that the world is not only not heading rapidly toward an unsustainable population by mid-century, but it's also poised for a population collapse.
In a tweet noted by Business Insider, the billionaire PayPal co-founder, responding to a post by World of Engineering citing a projected world population of 9,346,399,468 by 2050, refuted the warnings of overpopulation.
"1950 (historical) world population - 2,556,000,053," World of Engineering tweeted Thursday. "Current world population - 7,712,343,478[;] 2050 (projected) world population - 9,346,399,468."
"Real issue will [be] an aging & declining world population by 2050, *not* overpopulation," Musk responded. "[Jørgen] Randers estimate far more accurate than UN imo," Musk added, linking to a Wikipedia article containing several population projections, including by Randers.
In a follow-up tweet, Musk agreed with a follower that the population will be an "inverse pyramid," writing: "Yes, demographics, stratified by age, will look like an upside down pyramid with many old people & fewer young."
The report Musk cites contains several competing projections on the population by 2050, including the theory promoted by Randers in 2012 (footnotes removed):
Jørgen Randers, one of the authors of the seminal 1972 long-term simulations in The Limits to Growth, offered an alternative scenario in a 2012 book, arguing that traditional projections insufficiently take into account the downward impact of global urbanization on fertility. Randers' "most likely scenario" predicts a peak in the world population in the early 2040s at about 8.1 billion people, followed by decline.
These projected growth patterns depend on assumptions about vital rates. Total fertility is assumed to continue to decline, at varying paces depending on circumstances in individual countries, to a below-replacement level of 1.85 children per woman by mid century.
The report explains that Randers predicts that after countries drop below replacement level they will eventually begin to stabilize, elevating their fertility levels back to a replacement level. The models predict that by 2175, all countries will reach replacement fertility levels.
The report highlights how the United Nation's population projections have changed over the decades, current leading theories predicting that the population will not peak in the 21st century, as believed in the early 2000s, but will continue to grow in the next century (footnotes removed):
Estimates published in the 2000s tended to predict that the population of Earth will stop increasing around 2070; In a 2004 long-term prospective report, the United Nations Population Division projected the world population to peak at 9.22 billion in 2075. After reaching this maximum, it would decline slightly and then resume a slow increase, reaching a level of 8.97 billion by 2300, about the same as the projected 2050 figure.
This prediction was revised in the 2010s, to the effect that no maximum will likely be reached in the 21st century. The main reason for the revision was that the ongoing rapid population growth in Africa had been underestimated. A 2014 paper by demographers from several universities and the United Nations Population Division forecast that the world's population will reach about 10.9 billion in 2100 and continue growing thereafter. The UN as of 2017 predicts a decline of global population growth rate from +1.0% in 2020 to +0.5% in 2050 and to +0.1% in 2100.