2010 World Population Datasheet

This report from the Population Reference Bureau finds that while the global population reached its first billion at some point around 1800, the world’s population now grows by 1 billion about every 12 years. The 20th century began with 1.6 billion and, at the end of that century, those two numbers had simply reversed to 6.1 billion. If birth rates continue to decline in developing countries, the increase to 8 billion could take slightly longer. As developed countries undergo aging and little growth in population size, developing countries remain young and growing. Key findings can be found on the summary sheet here