The world’s population may reach 11 billion by 2100 - 2 billion more than previously anticipated - largely due to high birth rates on the African continent, according to a UN-led study. Can natural resources keep pace?

Researchers have long held the view that the number of people on the planet would grow to just 9 billion by 2100, and then stabilize or even decline. The latest analysis, however, indicates global population will increase by 4 billion by century’s end, according to a report published in Science journal.



"The consensus over the past 20 years or so was that world population, which is currently around 7 billion, would go up to 9 billion and level off, or probably decline," said co-author Adrian Raftery, professor of statistics and of sociology at the University of Washington.



"We found there's a 70 percent probability the world population will not stabilize this century," he added.



Much of the reason for the predicted population growth comes from Africa, where the population is expected to quadruple from 1 billion today to 4 billion by 2100.



"There is an 80 percent chance that the population in Africa at the end of the century will be between 3.5 and 5.1 billion people," said the study.



Global population is currently increasing at a rate of about 1.14 percent annually, while the average population change is estimated at about 80 million more people per year. The global population has doubled in 40 years from 1959 (3 billion) to 1999 (6 billion), according to World Population Clock.

It is now estimated that it will take another 43 years to increase by another 50 percent, reaching 9 billion by 2042.



Additionally, by 2030 India's population is expected to surpass China's, to become the most populous nation in the world. Meanwhile, Nigeria's population is predicted to surpass America's population by around mid-century to become the third-most populous country, reaching about 1 billion people in 2100.

Global demand for a growing planet

The analysis, formulated by UN and researchers at the University of Washington, Seattle, is said to provide a more accurate outlook than other studies in that it incorporates Bayesian statistics, which takes into account many different factors to arrive at a conclusion. It also uses data from the most recent UN population data, released in July."Earlier projections were strictly based on scenarios, so there was no uncertainty," said UN demographer Patrick Gerland."This work provides a more statistically driven assessment that allows us to quantify the predictions, and offer a confidence interval that could be useful in planning."

Predictions of 4 billion more people on the planet by 2100 places new emphasis on the issue of natural resources, many of which are already dwindling.



Consider fresh water resources, for example. According to the United Nations, water use has increased by more than twice the rate of population growth in the last century. By 2025, an estimated two-thirds of the world's population will live in "water-stressed regions" as a result of overuse, growth and climate change.



Another crucial natural resource is oil, which keeps the gears of the global economy lubricated. Although experts are divided as to how much oil reserves are still available, even the most optimistic predictions suggest that a decline will begin around 2020.



Writing in the prestigious scientific journal, Philosophical Transactions of the Royal Society (‘The Future of Oil Supply’, 2013), experts predicted “a sustained decline in global conventional production appears probable before 2030 and there is significant risk of this beginning before 2020.”



The growing demands of a growing global population is expected to place enormous pressure on various parts of the world, including in Asia, which is predicted to increase from its current 4.4 billion people to 5 billion in 2050, before it begins to stabilize.



Meanwhile, a more crowded planet will intensify problems such as infectious diseases and poverty. Africa, which is expected to experience the highest population growth by 2100, is presently in the grips of the deadly Ebola virus, which has already killed nearly 2,500 people.



However, such deadly diseases, including HIV, have largely been brought under control by the scientific community, and do not seem capable of offsetting high global birth rates.



So humans are left with a situation in which medical science has given them extended life spans and less likelihood of dying prematurely from deadly diseases, which, at the same time, places pressure on the planet and its finite store of resources.



How long such a contradiction can continue on an increasingly crowded planet remains the big question for scientists.



"Population, which had sort of fallen off the world's agenda, remains a very important issue," said Raftery.