The UN predicts that we will reach 9.1 billion in 2050, then the peak will occur around 2070 at 9.4 billion. But it is so far ahead and the margin of uncertainty is huge. We could easily end up with 1 or 2 billion more, or less.
NBF predicts a higher population because of better than expected life extension and pro-population growth policies in Europe and Asia and slower fertility declines in Africa. Prediction 11.5 billion by 2100. No peak in 2050.
Reasons for higher population
The UN assumes fertility in Africa, for example, will decline steadily from current levels of around four to five children, to around two. It might well go slower than that. Kenya, for example, had a fertility rate of nearly 8 in the 1960s, which came down to around 5 in the 1990s and has remained at that level. This was not expected by the UN, which expects things to go down steadily.
Governments in countries with very low birth rates are now considering implementing pro-natal policies. Most governments in Europe, I think, would like to see their birth rates go up a little bit. If that happens, there will be more Europeans, Japanese and Russians. Also, people might live longer than the UN predicts. The UN assumes that future increases in life expectancy will be slower than in the past. That may be wrong.
HIV is an example of a disease that people thought would stop growth or reduce Africa’s population. That didn’t happen. Population growth has such a powerful momentum even such a lethal and massive epidemic had only a fairly modest impact.
There are very few things that you can predict with any degree of accuracy 40 years from now. But the UN has a good record. In a projection made in 1950 it came close to predicting the actual 2000 population, so I would bet on there being a little over 9 billion people by 2050. Even so, the margin is still plus or minus a billion at least.