Environmental Problems, Their Causes, and Sustainability 1

ates affect a country’s population size and growthrate. The first type, replacement-level fertility, is thenumber of children a couple must bear to replace themselves.It is slightly higher than two children per couple(2.1 in developed countries and as high as 2.5 in somedeveloping countries), mostly because some femalechildren die before reaching their reproductive years.Does reaching replacement-level fertility mean animmediate halt in population growth? No, because somany future parents are alive. If each of today’s coupleshad an average of 2.1 children and their childrenalso had 2.1 children, the world’s population wouldstill grow for 50 years or more (assuming death ratesdo not rise).The second type of fertility rate is the total fertilityrate (TFR): the average number of children awoman typically has during her reproductive years.Good news. TFRs have dropped sharply since 1950 (Figure10-5). In 2004, the average global TFR was 2.8 childrenper woman. It was 1.5 in developed countries(down from 2.5 in 1950) and 3.1 in developing countries(down from 6.5 in 1950). The highest TFRs are inAfrica with a rate of 5.2 in 2004.So how many of us are likely to be here in 2050?Answer: From 7.2 to 10.6 billion, depending on theworld’s projected average TFR (Figure 10-6). Themedium projection is 8.9 billion people. About 97% ofthe growth in all three of these estimates is projected totake place in developing countries, where acutepoverty (living on less than $1 per day) is a way of lifefor about 1.4 billion people.WorldDevelopedcountries 1.62.8Developingcountries 3.1AfricaLatinAmerica 2.6AsiaOceaniaNorthAmericaEurope2.12.52.63.83.52.02.61.45 children per woman6.65.15.95.96.51950 2004Figure 10-5 Good news: decline in total fertility rates for variousgroupings of countries, 1950–2004. (Data from UnitedNations)Population (billions)1211109876543HighMediumLowMedium8.9High10.6Low7.221950 1960 1970 1980 1990 2000 2010 2020 2030 2040 2050YearFigure 10-6 UN world population projections, assuming that by2050 the world’s total fertility rate is 2.5 (high), 2.0 (medium), or1.5 (low) children per woman. The most likely projection is themedium one—8.9 billion by 2050. (Data from United Nations)How Have Fertility and Birth Rates Changedin the United States? Ups and DownsPopulation growth in the United States has sloweddown but is not close to leveling off.The population of the United States has grown from 76million in 1900 to 294 million in 2004, despite oscillationsin the country’s TFR (Figure 10-7) and birth rate(Figure 10-8, p. 180). A sharp rise in the birth rate occurredafter World War II. The period of high birthrates between 1946 and 1964 is known as the baby-boomperiod. This added 79 million people to the U.S. population.In 1957, the peak of the baby boom after WorldWar II, the TFR reached 3.7 children per woman. Sincethen it has generally declined and remained at or belowreplacement level since 1972.The drop in the TFR has led to a decline in the rateof population growth in the United States. But theBirths per woman4.03.53.02.52.12.01.51.00.5Baby boom(1946–64)Replacementlevel01920 1930 1940 1950 1960 1970 1980 1990 2000 2010YearFigure 10-7 Total fertility rates for the United States between1917 and 2004. (Data from Population Reference Bureau andU.S. Census Bureau)http://biology.brookscole.com/miller14179