Here is Jane Goodall at the World Economic Forum 2020 conference in Davos.
…all these things we talk about wouldn’t be a problem if there were—if there was—the size of population that there was five hundred years ago.
According to Worldometer, world population in 1500 was around 450 million. Today it is around 8 billion. So, to get from where we are to a “sustainable” population, you’d have to kill off around 95% of the current human population.
That’s another reference to the 500 million sustainable population figure dating back to the late 1960s that I mentioned in comment #3.