Population, Environment, and Development

Population

The world's population was half a billion in 1650 and reached 1 billion in 1804. By 1927, the population had doubled to 2 billion, and it reached 3 billion in 1959. In 2009, there were 6.8 billion people on the planet, and the world's population is projected to reach 9 billion by 2050. This rapid increase in human population can be attributed primarily to a dramatic decrease in the death rate, to technological advances, and to migration. The average life expectancy of people in developed countries has increased from 47 to 77 yrs. in the past century, while the average life expectancy in [Page 2241]developing countries has increased from 30 to 55 yrs. Advancements in technology, especially in agriculture due to the Green Revolution (the 1960s), have resulted in greater food availability. The advent of hybrid seeds with a range of environmental tolerance and the use of fertilizers have increased the production of crops, while food distribution methods improved both regionally and globally to satisfy demand. Improved sanitation (i.e., drinking water, waste management) and vaccinations for diseases (e.g., measles and smallpox) have also significantly contributed to the increase in the size of the world's population and in life expectancies. The migration of people to new regions of the world and increases in urban populations have resulted in cities with extremely high population densities over the past 200 yrs., especially in Asia. Indeed, currently, over 50% of the world's population lives in cities.

The world's population and growth rates are not evenly distributed around the globe. Until 1900, most of the world population resided in temperate regions. However, there has been a dramatic increase in the world's population in tropical regions and a significant increase in urban populations in the past 100 yrs. Geographically, Asia comprises 60% of the world's population, Africa 14%, Europe 11%, North America 8%, and South America 6% (Figure 1).

The six most populated countries in 2009 were China with 1.3 billion people, India with 1.2 billion people, the United States with 307 million people, Indonesia with 240 million people, Brazil with 199 million people, and Pakistan with 176 million people.

Models by the World Bank, the United Nations Population Division, and the Population Reference Bureau project population growth to reach a minimum of 9 billion people on the planet by 2100 if couples continue to have children at the current rate. The reason why the world's population is projected to exceed 9 billion to 10 billion people is the momentum built into very young age profiles. For example, half of the population in sub-Saharan Africa or Mexico is below 18 yrs. of age. Couples would have to have only one child for the next 30 yrs. to stabilize at the current levels. This pattern holds true even for countries such as China, which has had a one-child policy since the 1970s (though only enforced in urban areas), which has resulted in couples having families that are less than replacement size. However, China adds 514,000 new people every month because of the momentum built into the age profile, and it is projected to add another 100 million people by 2050.

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