The annual population growth rate increased from 2.22% in 1955 to 2.85% in 1985.
Then it went down to 2.47% in 2000 but then went back up to 2.60% in 2010-2015 and is now at 2.52%.
There is no firmly established downward trend in population growth in Africa.
For Africa’s population to only triple by 2080 would require a steady drop in population growth starting immediately and being maintained.
If Africa does not make the demographic transition for several decades then the world population will be several billion above the medium projection. This means instead of 11.2 billion people in 2100, it could be 15 to 18 billion.