Time in Years Until Population Is Halved Given TFR = 1

Peter D. Johnson of the US Census Bureau, International Programs Center, did a simulation using the International Data Base program of which he is an author.  He writes, “This shows the U.S. population dropping to half the 2005 population by about 2128 if the TFR drops to 1.0 immediately or by 2142 if the TFR drops to 1.0 by 2025.  In contrast, the world population would be halved by 2079 if the TFR were immediately cut to 1.0 or by 2094 if the TFR dropped to 1.0 by 2025.  The reason the U.S. takes longer is because of the assumed migration which offsets some of the losses due to the fertility declines.”  He sent the following figures along with tables of data and many more figures in Excel files:

The charts for the United States are based upon projected immigration statistics into the next century.  The charts for the world are based upon current life expectancies increasing linearly to US standards by 2100 and remaining constant thereafter.

Houston, Texas

January 2, 2005