Will Anderson (author of “This is Hope: Green Vegans and the New Human Ecology”) on the long term sustainable human population for the Earth (2013): “What is our sustainable human population from this biocentric perspective? Estimates vary. Somewhere near the middle is anthropologist Jeffrey K. McKee’s opinion. After stating that human population is the leading cause of extinctions, he asked what “… would it take before every country in our database demonstrated a reduction in threats to at least one or more species if mammals and birds? The answer is … approximately 3.4 billion [people] would accomplish this goal.” [77] Anthropologist J. Kenneth Smail believes the Earth’s long term sustainable population is 2 to 3 billion. [78] Some feel the sustainable population is much higher, though there is little said about what Earth would lose in the process. Opinions go as low as 500 million. [79]. … The organization “How Many People” estimates that “Every year about 135 million people are born and 55 million people die… “ [81]. If there were no births at all anywhere on Earth, the annual natural attrition would be 55 million fewer people per year. But of course we are still choosing to add nearly 80 million every year”” (Will Anderson, “This is Hope: Green Vegans and the New Human Ecology”, Earth Books, 2013, pages 23-24)
[Editor: the Earth's population in 2019 is 7.6 billion and is predicted to rise to about 10 billion by 2050].