The number of people added to the planet each year is in decline (blue) as fertility rates dip below replacement level in many countries. Still, the latest projections show that population will continue to grow throughout the 21st century, although more slowly than in recent decades (gray). World population doubled in just 40 years to reach 6 billion in 1999. It is now expected to reach 9 billion by 2044, an increase of just 50 percent over 45 years. Source: U.S. Census Bureau, International Data Base, June 2011 Update
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