What are the causes of rapid population growth

Population growth is known as one of the driving forces behind environmental problems, because the growing population demands more and more (non-renewable) resources for its own application. So why exactly does the human population expand to rapidly? To understand this, we must first explain a little about the difference between linear and exponential growth, in other words, add a little basic math to the equation.

Growth is usually thought of as a linear process: an increase by a constant amount over a period of time. The new amount is not influenced by the amount already present. For exponential growth, this is different, because the increase of a factor is proportional to what is already there. When cells divide, there will be a constant doubling of the cells already present. In terms of population growth, the numbers of people already present always influences the number of children born in any country. It is however not a simple matter of a constant doubling of the amount. Other factors, such as fertility and mortality rates, influence population growth, and the sexe and age of people already present, and rational decisions influence whether or not people will actually have one or more children.

Schematically, this can be represented as follows:

Population growth = birth rates – death rates

fertility mortality
(rationality, (health care, birth control, food availability,

relationships) resource availability)

So how rapid does our population grow? Meadows et al. (2004) state that in 1650 the human population counted only 0.5 billion heads. By 1900, the population had increased to 1.6 billion heads and was growing increasingly more rapidly, to 3.3 billion in 1965 (see figure). Not only the population itself was growing, but also the doubling time was decreasing, which basically means that growth itself was growing. This rapid growth increase was mainly caused by a decreasing death rate (more rapidly than birth rate), and particularly an increase in average human age. By 2000 the population counted 6 billion heads, however, population growth (doubling time) started to decline after 1965 because of decreasing birth rates.

The European population is now thought to decline in the future, because of a decreasing average number of children per family. Total world population continues to grow, but less rapidly because of population dynamics in developed countries.

Population growth for specific countries

China – China currently has the world’s largest population size and growth. In 1970 it was discovered that population growth in the country threatened the food supplies. Starting that year, efforts were made to control population growth, and simultaneously decrease it. The strictest birth control programme ever was introduced. Couples were urged to marry older, and have no more than one child. People that signed contracts to have no more than one child were provided with financial aid, and free educational opportunities for the child in question. Sterilization and other birth control methods were widely provided. Between 1970 and 2000 fertility rates dropped, and the number of children born per woman decreased, as well. But despite all the efforts made, the population still grew by 12 million heads, and it is projected to count 1.6 billion by 2050.

India – In 1990 its population achieved a size of one billion humans. Projections have been made that this number will increase to 1.63 million by 2050 at current growth rates. While some believe that increasing welfare and its additional measure such as birth control may solve the problems occurring in future India, many state that only governments aggressively reducing births may make a difference. The alternative is natural population growth control by mass starvation or disease, or control by crime and war.

Iran – After the Islamic Revolution in 1979 the Iranian population rapidly grew, from 34 million to 63 million in just 20 years. Birth rate per woman rose unbelievably, as everyone was encouraged to increase the Islamic population, and birth control was forbidden. The stimulation of giving birth and raising as many children as possible increased when the war broke out in 1980 and many young soldiers were killed. In the late 1990s the Iranian government became aware of the cost of such rapid population growth, and attempted to limit it by introducing mandatory family planning courses for couples. Birth control was now available, and educational programmes were organized. Currently, the population is still increasing, but only slowly. Birth rates per woman have dropped remarkably.

Nigeria – In 1950 the country had a population size of about 36 million humans. By the year 2000 this number had grown to 125 million. This is a nearly fourfold increase in population size in 50 years. If growth was unlimited by resource application, the population would increase eight more times before 2050. However, food shortages and environmental deterioration prevent such rapid growth.

Russia – The Russian population is currently declining by nearly 1 million people a year. Many different causes of this decline became apparent: demoralization of the population by a collapsing economy caused a decline in birth rates, pollution (see environmental disasters), poor nutrition and poor health care in many cases resulted in infertility, genetic defects or infant mortality, and many men died young because of drinking problems. All these factors together resulted in the lowest number of children per woman in the world.

Thailand – Before the 1970s, the Thai population was growing extremely rapidly. After 1971, a programme for population control was adopted, including a government-supported family planning programme, increases in women’s rights, including working possibilities, better health care and opportunities for birth control, and religious support for family planning. Vasectomies were particularly stimulated, and special clinics were opened everywhere. The number of births per woman fell, and the population stopped growing so rapidly. There is however still a major pollution problem for the government and the people of Thailand to deal with.

United States – In 1900 the United States population counted only 76 million heads, but by 1998 this had grown to 270 million. Birth rates per woman were particularly high after World War II in 1950, and have been steadily declining after that. The United States has the most rapidly expanding population of any developed country. The growth is more than double that of most other developed countries. It is estimated that the population will increase to nearly 340 million heads by 2050, and some environmental agencies even expect it to grow to over 500 million by than. Reasons for the expected population growth include increase in the number of young unmarried mothers, high fertility rates for some ethnic groups, and inadequate sexual education and birth control provision.

Sources

Cunningham W.P., Cunningham M.A., 2004, Principles of environmental science – Inquiry and applications, 2nd edition, McGraw Hill, New York, USA

Meadows D., Randers J., Meadows D., 2004, Limits to growth – the 30-year update, Bath Press, Bath, UK

Miller J.T. Jr., 1999, Living in the environment – Principles, connections and solutions, 11th edition, Brooks/ Cole Publishing Company, California, USA

World human population growth from 10,000 BC to 2019 AD. Data from: The United Nations

Human population growth impacts the Earth system in a variety of ways, including:

Increasing the extraction of resources from the environment. These resources include fossil fuels (oil, gas, and coal), minerals, trees, water, and wildlife, especially in the oceans. The process of removing resources, in turn, often releases pollutants and waste that reduce air and water quality, and harm the health of humans and other species.
Increasing the burning of fossil fuels for energy to generate electricity, and to power transportation (for example, cars and planes) and industrial processes.
Increase in freshwater use for drinking, agriculture, recreation, and industrial processes. Freshwater is extracted from lakes, rivers, the ground, and man-made reservoirs.
Increasing ecological impacts on environments. Forests and other habitats are disturbed or destroyed to construct urban areas including the construction of homes, businesses, and roads to accommodate growing populations. Additionally, as populations increase, more land is used for agricultural activities to grow crops and support livestock. This, in turn, can decrease species populations, geographic ranges, biodiversity, and alter interactions among organisms.
Increasing fishing and hunting, which reduces species populations of the exploited species. Fishing and hunting can also indirectly increase numbers of species that are not fished or hunted if more resources become available for the species that remain in the ecosystem.
Increasing the transport of invasive species, either intentionally or by accident, as people travel and import and export supplies. Urbanization also creates disturbed environments where invasive species often thrive and outcompete native species. For example, many invasive plant species thrive along strips of land next to roads and highways.
The transmission of diseases. Humans living in densely populated areas can rapidly spread diseases within and among populations. Additionally, because transportation has become easier and more frequent, diseases can spread quickly to new regions.

Can you think of additional cause and effect relationships between human population growth and other parts of the Earth system?

Visit the burning of fossil fuels, agricultural activities, and urbanization pages to learn more about how processes and phenomena related to the size and distribution of human populations affect global climate and ecosystems.