The U.N. said this month that the world's population reached 8 billion people, and more than half of the population growth up to 2050 would come from eight countries, five of them in Africa. In that time span, Nigeria is expected to double its population to 400 million people to become the world's third most populous nation. Experts warn that without proper planning, such growth would be unsustainable, as Timothy Obiezu reports from Abuja, Nigeria. Videographer: Emeka Gibson