PS Global population estimates and projections are notoriously difficult to juggle with even for polymaths, though. Even greatest among those.

In the early 1950s, Isaac Asimov described Trantor, the center of the Galactic Imperial Government, at the peak of its power as the enormously overpopulated ecumenopolis planet, where well in excess of 40 billions, mostly bureaucrats, were dwelling. Taking into account that the land surface of Trantor comprised 75,000,000 square miles in extent (additionally, Trantor had tunneled over a mile down), we obtain population density circa 1/30 of our modern Hong Kong’s, or even lower... Ouch!