Current projections by the UN's Population Division, based on the 2004 revision of the World Population Prospects database [3], are as follows.
Year Population (billions)
2010 6.8
2020 7.6
2030 8.2
2040 8.7
2050 8.9
Other projections of population growth predict that the world's population will eventually crest, though it is uncertain exactly when or how. In some scenarios, the population will crest as early as the mid-21st century at under 10 billion, due to gradually decreasing birth rates.
The projections keep changing. The rule seems to be that the greater the prosperity, the lower the birth rate.