World population hits 8 billion according to UN projections

Over the next three decades, the West African nation's population is expected to soar even more: From 216 million people this year to 375 million, the United Nations says, making Nigeria to the fourth most populous country in the world after only India, China and the United States.

Tuesday marks the UN projection for when the world's population is expected to hit 8 billion people, though officials are careful to note it's not a precise milestone.Nigeria is among the eight countries that the UN says will account for more than half the world's population growth between now and 2050 - along with Congo, Ethiopia and Tanzania, among others.Such rapid population growth also means more people vying for increasingly scarce water resources and potentially more families facing hunger as climate change increasingly impacts crop production.

In sub-Saharan Africa, the population is growing at 2.5% - more than three times the global average.Women in sub-Saharan Africa on average have 4.6 births each, twice the current global average of 2.3.Part of that can be traced to the high rate of child marriage, with 4 out of 10 girls married before they reach the age of 18, according to UN figures.

And the rate of teen pregnancy on the continent is the highest in the world, about half of the children born last year to mothers under 20 worldwide were in sub-Saharan Africa.