The next 20 years could well be dominated by the effects of climate change... which will disproportionately affect poorer nations and those subject to population pressures, and those on the climate front-line... in many cases, those countries in Africa. I think this will act as a further inhibitor on the rise of Africa, particularly as many African nations still have rapidly increasing populations.

There's a fascinating dynamic visualisation here detailing each country's progression across the five stage demographic transition model... it's apparent that many African nations are earlier on in the process.