World population has reached a transition point: The rapid growth of the second half of the 20th century has slowed. But factors such as continuously improving mortality and slower- than-expected declines in birth rates guarantee continued growth for decades. The questions remain: how fast, how much, and where?

 

The population size of the world’s more developed countries has essentially peaked. What little growth remains will mostly come from immigration from less developed countries. A number of more developed countries are likely to decline in size and see the proportion of their elderly populations rise to unprecedented levels. The outlook for less developed countries is quite different. The increase in world population from 1.6 billion in 1900 to 6.1 billion in 2000 was almost entirely due to population growth in those countries. The 20th-century population “explosion” was a direct result of the rapid decline in mortality rates in less developed countries.