Actually, the UN published a range of predictions, with the lowest 2100 population being only 7 billion. This study says 8.8 billion, which is 1-3 billion less than the UN’s worst case scenarios…
This study’s prediction for Africa, growing by an extra 2 billion people, seems highly speculative to me. It suggests they will primarily remain in poverty, even though they are the natural inheritor of the cheapest labor for factories, something that brought many Asian countries out of poverty.
I still believe that the global population peaking in 2050 is the most likely scenario.
By century’s end, 183 of 195 countries—barring an influx of immigrants—will have fallen below the replacement threshold needed to maintain population levels, an international team of researchers reported in The Lancet.
More than 20 countries—including Japan, Spain, Italy, Thailand, Portugal, South Korea and Poland—will see their numbers diminish by at least half.
China’s will fall nearly that much, from 1.4 billion people today to 730 million in 80 years.
Sub-Saharan Africa, meanwhile, will triple in size to some three billion people, with Nigeria alone expanding to almost 800 million in 2100, second only to India’s 1.1 billion.