Thursday, February 09, 2006

Human Population: Fundamentals of Growth

Human Population: Fundamentals of Growth
Population Growth and Distribution

In 2000, the world had 6.1 billion human inhabitants. This number could rise to more than 9 billion in the next 50 years. For the last 50 years, world population multiplied more rapidly than ever before, and more rapidly than it will ever grow in the future.

Anthropologists believe the human species dates back at least 3 million years. For most of our history, these distant ancestors lived a precarious existence as hunters and gatherers. This way of life kept their total numbers small, probably less than 10 million. However, as agriculture was introduced, communities evolved that could support more people.

World population expanded to about 300 million by A.D. 1 and continued to grow at a moderate rate. But after the start of the Industrial Revolution in the 18th century, living standards rose and widespread famines and epidemics diminished in some regions. Population growth accelerated. The population climbed to about 760 million in 1750 and reached 1 billion around 1800 (see chart, "World population growth, 1750–2150,").

World Population Distribution by Region, 1800–2050

Source: United Nations Population Division, Briefing Packet, 1998 Revision of World Population Prospects.

In 1800, the vast majority of the world's population (86 percent) resided in Asia and Europe, with 65 percent in Asia alone (see chart, "World population distribution by region, 1800–2050"). By 1900, Europe's share of world population had risen to 25 percent, fueled by the population increase that accompanied the Industrial Revolution. Some of this growth spilled over to the Americas, increasing their share of the world total.

World population growth accelerated after World War II, when the population of less developed countries began to increase dramatically. After millions of years of extremely slow growth, the human population indeed grew explosively, doubling again and again; a billion people were added between 1960 and 1975; another billion were added between 1975 and 1987. Throughout the 20th century each additional billion has been achieved in a shorter period of time. Human population entered the 20th century with 1.6 billion people and left the century with 6.1 billion.

The growth of the last 200 years appears explosive on the historical timeline. The overall effects of this growth on living standards, resource use, and the environment will continue to change the world landscape long after.
Exponential Growth

As long ago as 1789, Thomas Malthus studied the nature of population growth in Europe. He claimed that population was increasing faster than food production, and he feared eventual global starvation. Of course he could not foresee how modern technology would expand food production, but his observations about how populations increase were important. Population grows geometrically (1, 2, 4, 8 …), rather than arithmetically (1, 2, 3, 4 …), which is why the numbers can increase so quickly.

A story said to have originated in Persia offers a classic example of exponential growth. It tells of a clever courtier who presented a beautiful chess set to his king and in return asked only that the king give him one grain of rice for the first square, two grains, or double the amount, for the second square, four grains (or double again) for the third, and so forth. The king, not being mathematically inclined, agreed and ordered the rice to be brought from storage. The eighth square required 128 grains, the 12th took more than one pound. Long before reaching the 64th square, every grain of rice in the kingdom had been used. Even today, the total world rice production would not be enough to meet the amount required for the final square of the chessboard. The secret to understanding the arithmetic is that the rate of growth (doubling for each square) applies to an ever-expanding amount of rice, so the number of grains added with each doubling goes up, even though the rate of growth is constant.

Similarly, if a country's population begins with 1 million and grows at a steady 3 percent annually, it will add 30,000 persons the first year, almost 31,000 the second year, and 40,000 by the 10th year. At a 3 percent growth rate, its doubling time — or the number of years to double in size — is 23 years. (The doubling time for a population can be roughly determined by dividing the current growth rate into the number "69." Therefore, 69/3=23 years. Of course, if a population's growth rate does not remain at this rate, the projected doubling time would need to be recalculated.)

The 2000 growth rate of 1.4 percent, when applied to the world's 6.1 billion population, yields an annual increase of about 85 million people. Because of the large and increasing population size, the number of people added to the global population will remain high for several decades, even as growth rates continue to decline.

Between 2000 and 2030, nearly 100 percent of this annual growth will occur in the less developed countries in Africa, Asia, and Latin America, whose population growth rates are much higher than those in more developed countries. Growth rates of 1.9 percent and higher mean that populations would double in about 36 years, if these rates continue. Demographers do not believe they will. Projections of growth rates are lower than 1.9 percent because birth rates are declining and are expected to continue to do so. The populations in the less developed regions will most likely continue to command a larger proportion of the world total. While Asia's share of world population may continue to hover around 55 percent through the next century, Europe's portion has declined sharply and could drop even more during the 21st century. Africa and Latin America each would gain part of Europe's portion. By 2100, Africa is expected to capture the greatest share (see chart, "World population distribution by region, 1800–2050", above).

The more developed countries in Europe and North America, as well as Japan, Australia, and New Zealand, are growing by less than 1 percent annually. Population growth rates are negative in many European countries, including Russia (-0.6%), Estonia (-0.5%), Hungary (-0.4%), and Ukraine (-0.4%). If the growth rates in these countries continue to fall below zero, population size would slowly decline. As the chart "World population growth, 1750–2150" shows, population increase in more developed countries is already low and is expected to stabilize.

Birth rate (or crude birth rate): The number of live births per 1,000 population in a given year. Not to be confused with the growth rate.

Doubling time: The number of years required for the population of an area to double its present size, given the current rate of population growth. Population doubling time is useful to demonstrate the long-term effect of a growth rate, but should not be used to project population size. Many more developed countries have very low growth rates and, as a result, the equation shows doubling times of hundreds or thousands of years. But these countries are not expected to ever double again. Most, in fact, likely have population declines in their future. Many less developed countries have high growth rates that are associated with short doubling times, but are expected to grow more slowly as birth rates are expected to continue to decline.

Growth rate: The number of persons added to (or subtracted from) a population in a year due to natural increase and net migration; expressed as a percentage of the population at the beginning of the time period.

Less developed countries: Less developed countries include all countries in Africa, Asia (excluding Japan), and Latin America and the Caribbean, and the regions of Melanesia, Micronesia, and Polynesia.

More developed countries: More developed countries include all countries in Europe, North America, Australia, New Zealand, and Japan.


Post a Comment

<< Home