Population - Facts and Figures

SOME POPULATION FACTS AND FIGURES:

The world's human population currently numbers about 5.8 billion people, and the figure grows by nearly 90 million people each year, or around 240,000 each day.1 This annual addition to population is greater than ever before in history prior to the 1980s. It stems in large part from the unprecedented size of current population. The growth rate itself has actually declined since 1970, from about 2 percent to about 1.5 percent today. However, because this rate is applied to a much larger population than in 1970–when world population stood at 3.7 billion people–the added yearly increments are larger. If the population growth rate is not reduced further, world population will double by the year 2040.2

It took all of history up to the early 1800s for world population to reach 1 billion people, and until 1960 to reach 3 billion. Today, the world gains 1 billion people every 11 years.3

Population in most industrialized countries continues to grow through either natural increase (resulting from more births in a country than deaths) or immigration, or both. In the United States, natural increase is about 0.6 percent a year, while total population growth is around 1 percent. Nonetheless, more than 90 percent of the world's population growth is occurring in developing countries in Asia, Africa and Latin America. The rates of natural increase on these continents vary, however, from 1.6 percent in Asia and 1.9 percent in Latin America and the Caribbean to 2.8 percent in Africa.4

While Asia¹s population growth rate is lower than those of Latin America and Africa, the vast continent has three fifths of the world¹s people and thus adds more people to world population than any other continent. Population density is also greatest in Asia, with more than 282 persons per square mile. This compares with 60 persons per square mile in Latin America and the Caribbean, 62 persons per square mile in Africa, and 73 persons per square mile in the United States.5 Comparisons of population density can be misleading, however, since the natural resources on which human life depends‹fresh water, farmland and forests, for example‹are unevenly distributed across islands and continents.

It is not physically possible for population growth to continue for long at today¹s levels. The current size of human population, and the additions made to it each year, are unprecedented in history. There is also the sheer power of continuing exponential growth to consider. One demographer calculated in 1974 that at then-current growth rates, in seven centuries only one square foot of land would be available for each human being. Within 6,000 years, the mass humanity would form a sphere expanding outward from the earth at the speed of light.6 Population growth rates have declined since the publication of these calculations, but the point remains. Growth rates similar to those of today cannot continue indefinitely.

The power of exponential growth is sometimes illustrated by the story of a pond lily that doubles its extent every day. If it takes the lily a year to fill the pond, it takes a full 364 days to fill half the pond. Only on the last day of the lily's expansion are the limits obvious. Human beings are not lilies. Nonetheless, they, too, need water, air and nutrients to survive, and the planet¹s supply of all of these is finite. Within a century or two‹a blink of an eye in humanity's time on earth‹population growth will decline significantly from current rates or end altogether. Today's rapid population growth is thus a relatively brief interlude in humanity's experience. The biggest question is whether this growth will slow or end due to decreases in birth rates or increases in death rates, or both. In the words of writer Joel E. Cohen, "The finiteness of the Earth guarantees that there are ceilings on human numbers."7

Even if a considerably larger population than today¹s could live safely and sustainably, in balance with the earth¹s resources, population momentum would remain a concern. Population momentum is the tendency of any population with a fairly young age structure (based on past rapid growth) to continue growing for some time after women begin having two children each on average. (This is called "replacement fertility," because each couple replaces themselves numerically in the larger population.) When there are many people of childbearing age and relatively fewer old people near the end of their lives, even two-child families on average will produce births well in excess of deaths, and this will be true until roughly equal numbers of people are in each age group. The colossal momentum of population growth has been compared to the long stopping distance of a large, fully loaded truck. Because of past population growth, an unusually high proportion of today's world population consists of young people just entering their childbearing years. This contributes to the substantial population momentum that is a critical demographic factor today, and will be for some time.  Demographers project that if women began having just two children on average today, population would still grow from today's 5.8 billion to more than 8 billion before stabilizing in the next century.

The power of population momentum, along with other drivers of population growth, multiplies the physical momentum embedded in two of the most worrisome environmental trends. In the case of climate change, global temperatures are likely to continue climbing for decades even after concentrations of heat-trapping greenhouse gases reach stable levels in the atmosphere. This is because the oceans store vast amounts of heat in their depths, which delays the greenhouse warming experienced at the earth¹s surface. In the case of the extinction of plant and animal species, the populations of some of these species may be past reviving due to current loss of habitat or over-harvesting by humans, but individuals of the species may linger for several more generations. The future growth of human numbers, some of it from population momentum, adds to the pressures that build momentum into climate change and the ongoing loss of biological diversity.