7 Billion: Will Earth Really Hit Population Milestone Monday?
Differing projections highlight challenges in estimating population, experts say.
But why did the UN choose October 31? And why does the seventh-billion date differ from other projections? The U.S. Census Bureau, which also attempts global population projections, predicts humanity won't hit the seventh-billion milestone until March 12, 2012, for example.
In theory, estimating when the world population will reach seven billion is simple: Take the last known population numbers for each country from its last census, subtract the number of people you think have died, and add the number of people that you think will be born, as well as the population change expected from migration.
In practice, of course, it's more complicated.
For example, "some governments don't have strong statistical systems in place, or sometimes the
