Economists, demographers, and other social scientists divide the 200 countries of the world into two groups-- more-developed countries (MDCs) and less-developed countries (LDCs). This distinction is based primarily on a country's degree of industrial and technological development and its per-capita gross national income.
The table below (from www.prb.org) compares a few of the demographic traits of these two "worlds" (as of mid-year 2012).
Of particular importance in understanding future population growth are the following.
1. "rate of increase" is the annual growth rate of the population.
2. "doubling time" is how many years are required for the population to double in size. It is not a "prediction," but rather a projection of growth based on an unchanging current rate of growth. Doubling time historically has been used to comprehend very rapid rates of growth.
3. "% of population under the age of 15" indicates the size of the population from which future population growth will occur. It indicates population "growth momentum."
4. "predicted 2050 population" is the U.N.'s prediction of population size in 2050.
If you do the math, you will find that 96% of the 2.566 billion people added from now until 2050 will be in less developed countries. But, before you jump to embarrassing conclusions, consider that well-intentioned people in MDCs brought this population increase about. More about this in future posts.
See also "Human Population I: Size and Growth" (13 February 2013) and "Human Population II: Billion-by-Billion" (25 February 2013).