The world's population is expected to keep growing throughout the 21st century, and the number of people on this planet could reach a whopping 11 billion by the year 2100; this is about two billion higher than has been previously estimated.
A University of Washington and the United Nations research team reported the most up-to-date numbers for future world populations and described a new method for making these estimates.
"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," corresponding author Adrian Raftery, a UW professor of statistics and of sociology, said. "We found there's a 70 percent probability the world population will not stabilize this century. Population, which had sort of fallen off the world's agenda, remains a very important issue."
The findings are based on the most recent United Nations population data released in July, which was the first UN report to use modern statistics known as Bayesian statistics.
Most of the anticipated growth lies in Africa; in this region the population could quadruple from about one billion to four billion by only the end of the century. Other regions of the world are expected to see less dramatic changes: Asia is now at 4.4 billion people but is expected to peak at five billion in 2050 and start declining; North America, Europe and Latin America and the Caribbean are expected to stay at a population of about one billion each.
"Earlier projections were strictly based on scenarios, so there was no uncertainty," said first author Patrick Gerland, a demographer at the U.N. "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."
The findings are based primarily on future life expectancy and fertility rates, and employs statistical methods to combine government data and expert forecasts.
"This paper brings together the research from the past seven years, and also brings in recent data," Raftery said. "We can answer questions about future population growth using standard principles of statistical inference, which has never really been done before."
A rising population could have significant effects on global issues such as climate change, infectious disease and poverty.
