It took only a dozen years for humanity to add another billion people to the planet, reaching the milestone of 7 billion Monday — give or take a few months.
Demographers at the United Nations Population Division set Oct. 31, 2011, as the "symbolic" date for hitting 7 billion, while acknowledging that it's impossible to know for sure the specific time or day. Using slightly different calculations, the U.S. Census Bureau estimates the 7-billion threshold will not be reached until March.
Under any methodology, demographers agree that humanity remains on a steep growth curve, which is likely to keep climbing through the rest of this century. The U.N.'s best estimate is that population will march past 9.3 billion by 2050 and exceed 10.1 billion by the end of the century. It could be far more, if birthrates do not continue to drop as they have in the last half-century.
Nearly all the projected growth this century is expected to occur in developing countries in Asia, Africa and Latin America, while the combined populations in Europe, North America and other wealthy industrialized nations will remain relatively flat. Some countries, such as Germany, Russia and Japan, are poised to edge downward, their loss made up mostly by ongoing growth in the United States, which is bolstered by waves of immigrants.
The buildup to Monday's milestone has briefly turned up the flame on long-simmering debates about growth on a finite planet: Whether a growing population or growing consumption remains the biggest environmental challenge, how best to help lift a billion people out of poverty and misery, whether governments should provide contraception for those who cannot afford it.