We are living in a world of unprecedented demographic change. After growing very slowly for most of human history, the world's population more than doubled in the last half century to reach 6 billion in late 1999. And, in late 2011, it will surpass 7 billion. Lower mortality rates, longer life expectancy and large youth populations in countries where fertility remains high all contributed to the rapid population growth of recent decades.
According to the 2010 Revision, the world population is expected to hit 10.1 billion by 2100, reaching 9.3 billion by the middle of this century. Essentially all of the growth will take place in less developed countries and will be predominately among the poorest populations in urban areas.
Between 2011 and 2100, the population of high-fertility countries, which includes most of sub-Saharan Africa, is projected to triple, passing from 1.2 billion to 4.2 billion. During the same period, the population of intermediate-fertility countries, such as the United States, Mexico and India, will increase by just 26 per cent, while that of low-fertility countries, which includes most of Europe, China and Australia, will decline by about 20 per cent.
Ultimately, the populations of high-fertility countries are projected to decline until reaching the replacement rate of 2.1 children per woman by the end of the century. However, these projections assume wider availability of family planning services, and small variations in fertility can produce major differences in the size of populations over the long run.
If high-fertility countries do not achieve the reductions projected, they may well see their overall population increase four- or five-fold by the turn of the century (instead of a three-fold increase). This underscores the importance of expanding access to family planning, especially in the poorest countries where growth rates are fastest.
Clearly, most people want and are having smaller families than in the past. This trend has been greatly helped by the wider availability of high quality, safe and affordable family planning services. Still, many people are having more children than they want to. Some 215 million women who would like to use contraceptives lack access to them.