Using a new probabilistic statistical method, which involved creating 10,000 population projections for each country, demographers from the University of Washington and the UN Population Division have projected that by 2100, the earth’s population could reach 10.9 billion people. The demographers published their findings in a paper in the journal Science.
They argue that there is an 80% probability of hitting somewhere within the range of 9.6 billion at the low end and 12.3 billion at the high end by the end of the century, with 10.9 being the median of the projected outcomes.
Among the interesting statistics you’ll find in the article: sub-Saharan Africa could reach the population density level of China today, and one in five people added to the planet during this century will be born in Nigeria, Africa’s largest country.
Population projections are influenced by the base data used (which changes with each new projection because new census and survey data becomes available) and by assumptions made about the future fertility, mortality, and migration patterns of each country’s residents. Therefore, depending on the data and assumptions used, projection outcomes will vary. For example, the most recent UN probabilistic population projections, released in 2015, calculated a median projection of 11.2 billion people in 2100, with an 80% probability that it will be between 10 billion and 12.5 billion.