Throughout most of human history, the world's population has grown gradually. It took thousands of years for the global population to reach one billion people (around 1800). Then, in a little more than a century, the population jumped to two billion (by 1960), and to three billion by 1980. In just twenty years—between 1980 and 2000—the world's human population doubled from three billion to six billion people.
Billboard promoting birth control, China, 1984. (UPI/Corbis-Bettmann. Reproduced by permission.)
The human population explosion during the past century was the result of several factors. Fertility rates remained high, while medical and agricultural advances such as antibiotics, immunizations, clean water, and improved food availability reduced mortality rates—especially among infants and children.
It is difficult to predict how rapidly the human population will continue to increase, due to the many factors that affect population growth. Another important question that scholars ask is "How many people can the earth support?" While the human population grows, the earth's size and resources remain the same. Technology can increase the amount of food that can be produced on a piece of land, but it cannot increase the amount of land and water on the planet. Many people regard population growth as the single most serious global issue, because population size is closely linked to environmental and human health conditions.
Environmental problems are aggravated by population explosions. More people means more resources and energy are consumed and more pollution is created and more waste is sent to landfills. More land is needed to grow crops and build houses. More trees are cut down for new homes. More cars are built, more fossil fuels are used, and more gases are released into the environment. More natural wilderness areas or beautiful landscapes are destroyed to provide resources and cropland. In short, population growth makes other environmental problems harder to solve.
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