The title asks about ten billion people. Although the ten billion may be taken as a stipulation, a few words can establish it is a reasonable one. Figure 2.1 shows the population of the regions of the world since 1950 and projects them to 2025 A.D. (United Nations, 1991[UN:91]). Projected annual increments exceeding 80 million during the first decades of the twenty-first century and a total of 8.5 billion for 2025 establish that ten billion is not excessive. On the other hand, the relative rate of annual increase, which exceeded 2% from 1965-1970, was smaller from 1985-1990 and is projected to be only 1% from 2020-2025. The declining rate establishes that we can postpone asking how much land more than ten billion people can spare.
Figure 2.1. The rising populations of the regions of the world. The population of Oceania, which rose from 13 million in 1950 and is expected to reach 38 million in 2025, was omitted (United Nations, 1991).[UN:91]
Asia's large portion of the world's population is no surprise. Nor are the steady absolute and declining fractions in the former Union of Soviet Socialist Republics (USSR), Europe, and North America. Africa provides the surprise.
Comparing their 1988 and 1990 projections, the experts of the United Nations (U.N.) highlighted their increased estimates for Ethiopia, Cameroon, and ten other African countries. They raised their estimates of total fertility rate in 16 countries substantially. Among large countries, increases from 1950 to 2025 of 13-fold in Kenya and 11-fold in Tanzania lead. The experts projected no fall in life expectancy in Africa although life expectancy will be shorter in Africa in 2025 A.D. than in any other region-as it is today. Nevertheless, by 2025 AD. life should be much longer in Africa than it is today. Unimpressed by the impact of AIDS on population growth, the experts expect simple aging of the world's people rather than disease to slow the improvement of the world's crude death rate.
To estimate a population for 2050 AD., Parikh (1993a)[Par3a] extended the time trends of the United Nations from 2025. Using medium and high regional projections, he estimated populations of 10 and 13 billion in 2050.
Asking how much land ten billion people can spare is reasonable.