We have 7 billion now with 1 billion in the Americas, 1 billion in Europe and Russia, 1 billion in Africa, and 4 billion in Asia.
By 2050 Africa will as a second billion and Asia a 5th billion for a 9 billion total.
By 2100 Africa will add a 3rd and 4th billion for 11 billion total.
That's where it tops out, so say the demographers.
by 2050/2100 we will have imported a billion from Africa and Asia probably, mostly Muslims.