A few weeks ago this site had noted that the world population projections were too low. The UN previously predicted would reach 9.1 billion in 2050, then the peak will occur around 2070 at 9.4 billion.
A large life extension breakthrough in 2020 would add a maximum of about 4 billion people by 2100. This would have less impact on population than the high fertility versus midrange fertility scenario.
The high projection variant, whose fertility is just half a child above that in the medium variant, produces a world population of 10.6 billion in 2050 and 15.8 billion in 2100. The low variant, whose fertility remains half a child below that of the medium, produces a population that reaches 8.1 billion in 2050 and declines towards the second half of this century to reach 6.2 billion in 2100. For long-term trends the medium variant is taken as reference.
The medium-variant projection for 2050 is more certain than for 2100 because people who will be 40 years and older in 2050 are already born. According to the medium variant, it will take 13 years to add the eighth billion, 18 years to add the ninth billion and 40 years to reach the tenth billion. According to the high variant, an additional billion would be added every 10 or 11 years for the rest of this century.
Countries as varied as China, Brazil, the Russian Federation, Japan, Viet Nam, Germany, the Islamic Republic of Iran, Thailand and France, in order of population size, account for 75 per cent of the population living in low-fertility countries. Three-quarters of the population living in the intermediate-fertility countries is located in India, the United States of America, Indonesia, Bangladesh, Mexico and Egypt, in order of population size; and Pakistan, Nigeria, the Philippines, Ethiopia, the Democratic Republic of the Congo, the United Republic of Tanzania, Sudan, Kenya, Uganda, Iraq, Afghanistan, Ghana, Yemen, Mozambique and Madagascar, in order of population size, account for 75 per cent of the population of high-fertility countries.
With medium fertility the US would have 478 million people in 2100 and with high fertility the US would have 705 million in 2100.
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