According to the United Nations (UN), the 31st of October 2011 is the day the world’s population officially reaches seven billion. However, it is not possible to absolutely calculate at which point in time the seven billionth person will be born. The US Census Bureau does not estimate the population reaching seven billion until February 2012, so the 31st of October is more symbolic. However, sometime in the very near future the world’s population will reach this milestone.
The first billion was reached sometime in the late 1700s–1800s and approximately 130 years later the population of the world doubled to two billion. However from the 1950’s onwards we have seen a rapid growth in population. According to the UN report “State of World Population
The rapid growth of the world population started in 1950, with reductions in mortality in the less developed regions, resulting in an estimated population of 6.1 billion in the year 2000, nearly two-and-a-half times the population in 1950. With the declines in fertility in most of the world, the global growth rate of population has been decreasing since its peak of 2.0 per cent in 1965-1970.
The UN predicts that the population of the world will reach 9.3 billion by the middle of this century and 10.1 billion within 90 years.
Population growth is slowing (as seen in the graph above) due in part to lower fertility rates, however this has been partially offset by improvements in health which has in turn increased life expectancy. For example, infant mortality has dropped from about 133 deaths per 1000 births (1950s) to 46 per 1000 (2005-2010). However the number of children a woman is expected to have in her reproductive years (fertility rate) has dropped by more than half, from 6.0 to 2.5. According to the UN, in the more developed countries, the average fertility rate is about 1.7 births—below the replacement rate of 2.1 births—compared to developing countries where the rate is about 4.2. Therefore, population will continue to grow in those developing nations, but slow in countries where the replacement rate is not being met. The result is that each year around 80 million people are added to the world’s population.
The most populous countries in the world are China (1.35 billion) and India (1.24 billion). However the fertility rate for China is 1.6 compared to 2.5 in India and according to the “State of the World Population” report,
...by 2025 India will have 1.46 billion people and will have overtaken China with 1.39 billion. China’s population will then, based on a medium variant, decline to about 1.3 billion by 2050. India will continue to grow to about 1.7 billion by 2060 before beginning to decline.
The table below lists the top ten most populous nations as estimated by the UN in 2011, these countries contain 58.6 per cent of the world’s population. Australia is ranked 55th and, with a fertility rate of 1.9 which is below replacement rate, our population will only increase via immigration.
Of the seven billion people, 43 per cent are under the age of 25 and 13 per cent are over the age of 60 (893 million people). The UN predicts that those aged over 60 will increase to 2.4 billion by the middle of this century.
United Nations, The state of World Population, 2011