Alexandre Meneghini, File / AP Photo
It may not be flat, but the world is definitely hot and crowded: the global population will reach 7 billion this month, according to the U.N. Population Fund. The world has added another billion people since 1998, when the planet reached the 6 billion milestone, and is expected to add yet another by 2025. Since most Western nations have slowed their population growth, the boom will come in African cities where birthrates are high and poverty is most extreme. By 2025, as many as 1.8 billion will be living in areas with severe water shortages and, without major family-planning initiatives, could see unprecedented hunger. "Extreme poverty and large families tend to reinforce each other," said one environmental analyst. "The challenge is to intervene in that cycle and accelerate the shift to smaller families."