During the past 50 years, the world’s population has increased dramatically – a trend that is projected to continue. Most future growth will occur in less developed countries, where the population is increasing more than five times as fast as that in developed countries.
The phenomenal growth in world population has occurred despite a marked decline in the growth rate of the world’s population – which fell to 1.2 percent a year in 2000–05, and is expected to drop further to 0.38 percent a year by 2045–50 – because of the large number of women of childbearing age, a phenomenon known as “population momentum.”
Birth rates have fallen and are expected to drop further in less developed countries, whereas in more developed countries, they are expected to remain fairly constant. At the same time, death rates are holding fairly steady.
Male/female sex ratios are typically around 105/100 at very young ages because naturally more boys than girls are born, with sex ratios tending to equalize by adulthood, as more males than females die. However, in some countries, female infanticide, neglect of female newborns, and selective abortion of female fetuses have resulted in male/female ratios of over 108/100 at very young ages.
Declining birth rates, combined with increases in life expectancy, are leading to population aging. The number of people in less developed countries aged 60 or over is expected to exceed the number of 12- to 24-year-olds by 2045, a phenomenon that occurred in more developed countries in the late 1990s.
Increases in the median age – the age at which 50 percent of the population is older and 50 percent is younger – are another way of looking at population aging. The current 13-year difference in median age between developed and developing countries is much larger than it was 60 years ago.
As countries develop, people tend to move from rural to urban areas. The world’s urban population is expected to grow by 1.8 percent a year between 2000 and 2030, almost twice as fast as global population growth. By 2007, the majority of the global population will be urban and the number of urban dwellers will rise from 3 billion in 2005 to 5 billion in 2030.
People are also continuing to move from one country to another, with developed regions gaining 2.6 million immigrants annually during 1990–2000. About half of that flow was to North America. Asia was by far the largest source of migrants (1.5 million a year), followed by Latin America and the Caribbean (0.8 million a year) and Africa (0.3 million a year).
Based on United Nations, World Population Prospects 2004. Prepared by Larry Rosenberg and David Bloom (Harvard University).
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