They say that there's likely to be 9.8 billion by 2050 and then 11.2 billion by 2100. For it's based upon an assumption and that assumption is highly suspect. It's also true that the various UN population predictions have always been on the upside of reality. I strongly suspect that not enough attention is being paid to how the reduction in poverty changes fertility levels. We see a direct connection between GDP per capita and fertility levels.

Source: Forbes June 22, 2017 15:33 UTC