What’s the News: The world’s population is projected to reach 7 billion this October and continue climbing, reaching 10.1 billion by the end of the 21st century, says an official United Nations report (PDF) released earlier this week. This is a significant departure from earlier projections that said the population would peak at just over 9 billion, then level off and even slightly decline.

How the Heck:

Projecting the world population is based on looking at fertility and mortality rates, and how they may be affected by government policies, available services, and behavior. Starting with a few possible fertility and mortality trajectories, researchers in the Population Division of the UN Department of Economic and Social Affairs work out what those would mean for overall population.
These projections differ from earlier ones because fertility rates in many developing countries—particularly in Africa—aren’t declining as quickly as demographers had thought they would. Nigeria, for instance, is currently the most populous country in ...