structural:summarization, quality:correction
Carrying capacity

Attempts have been made to estimate the world's carrying capacity for humans; the maximum population the world can host. A 2004 meta-analysis of 69 such studies from 1694 until 2001 found the average predicted maximum number of people the Earth would ever have was 7.7 billion people, with lower and upper meta-bounds at 0.65 and 98 billion people, respectively. They conclude: "recent predictions of stabilized world population levels for 2050 exceed several of our meta-estimates of a world population limit".

A 2012 United Nations report summarized 65 different estimated maximum sustainable population sizes and the most common estimate was 8 billion. Advocates of reduced population often put forward much lower numbers. Paul R. Ehrlich stated in 2018 that the optimum population is between 1.5 and 2 billion. In 2022 Ehrlich and other contributors to the "Scientists' warning on population", including Eileen Crist, William J. Ripple, William E. Rees and Christopher Wolf, stated that environmental analysts put the sustainable level of human population at between 2 and 4 billion people. Geographer Chris Tucker estimates that 3 billion is a sustainable number.