Can 11 billion people survive on this planet?

By 2100, there could be an extra four billion people roaming the planet – making it difficult to discern whether Earth will have enough resources to support the birth of practically another planet-worth of people. (Earth hit four billion in 1974).

That’s 11 billion people total, according to a new study by the University of Washington and the United Nations. The running estimate for total world population was that it would hover at 9 billion and then level off or decline, but the new UW study shows we are in for many more neighbors than that.

Where they’ll be 

Most of the growth will be in Africa, according to the UW study, where there is an 80 percent chance that the population will quadruple from around one billion to between 3.5 and 5.1 billion by the end of the century.

Asia, which has a population of 4.4 billion, will peak to about five billion in 2050, then decline. By 2030, India’s population is projected to surpass China’s, becoming the most populous country in the world. Populations in North America, Europe, and Latin America and the Caribbean will each stay below one billion.

“A rapidly rising population could exacerbate challenges in the availability of natural resources and put considerable pressure on public health systems, particularly in poorer countries, making it harder to respond to infectious disease epidemics,” said Adrian Raftery, UW professor of statistics and sociology and corresponding author.

More people means more natural resources being used. According to the UN, as a result of overuse, growth and climate change, about two-thirds of the world’s populations will be considered “water-stressed regions” by 2025.

Behind the number

The findings, gathered by the UN and UW researchers, incorporate Bayesian statistics, which combine all available information to generate better predictions and provide a more accurate account than other studies.  It also incorporates data from the most recent UN population data.

According to the study, world population projections are based on life expectancy and fertility rates. If either changes, the projections shift.

Africa has some of the highest fertility rates in the world, making it difficult to accurately predict whether the infertility rate will decrease over the next century.

The UN and UW researchers used statistical methods based on combined government data and expert forecasters to estimate mortality and fertility rates, as well as international migration.

“An alternative way to [predict fertility rates] would be to project forward education rates, and then use these projections as a basis for projecting fertility.  The problem with this is that we don’t know future education rates, and forecasts of these are subject to error.”

Silver linings 

However, there is a “silver lining,” said Raftery. If Africa can reduce their high fertility rates faster, there will be more resources available for investment in infrastructure, education, and health and environmental protection, he adds.

“There is no consensus among experts about how many people the earth could sustain, but estimates range up to well above the UN extreme upper bound of 13 billion in 2100,” Raftery said.

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