By the dawn of the 22nd century, the world will likely have over 11 billion people.
This explosive growth is going to be lopsided, though.
In most developed countries, the birth rates are stagnant or declining.
And in developing countries, birth rates are skyrocketing.
The United Nations projects that half of the population growth for the entire world from now until 2050 will occur in only nine countries: India, Nigeria, Pakistan, Democratic Republic of the Congo, Ethiopia, United Republic of Tanzania, the United States, Indonesia, and Uganda.
And by 2100, the world's biggest cities will be concentrated in Southeast Asia and Africa.
Based on population growth models, the Global Cities Institute at the University of Toronto projects these will be the 10 biggest cities in 2100.