Henry Grabar, fellow at The Atlantic Cities, writes on the findings of a team of scientists from two universities in Spain, the Autonomous University of Madrid and CEU-San Pablo University.
According to their model, the 2011 report (summarized here) by the United Nations population division is way off, which means many of the dire projections on resource consumption and carbon emissions may have to be adjusted,
In 2011, the United Nations population division predicted a global population of 10.1 billion by 2100, an increase of nearly 50 percent from the earth's current population of 7 billion. In the U.N. models, only the low-fertility curve showed the possibility for population decline in the 21st century.
If the Spanish model is correct, global population will "peak in 2050 slightly above eight billion, and then fall back to 6.2 billion by the end of the century, the same as the total world population back in 2000."
Why the disparity?
Population projections try to predict the battle between two trends: the drop in the mortality rate and the decline in the birth rate. UN population estimates, national and global, have documented the progress from a high-mortality, high-fertility society to one with low mortality and low fertility [PDF]. Declining fertility has followed declining mortality, meaning that national populations have tended to rise before they stabilize and, eventually, fall.
In essence, key to projections are whether models closely adhere to the low fertility rate or the high fertility rate. The Spanish model takes the former approach while in 2011, the U.N Population Division took the latter.
There is some evidence in support of the UN's low-fertility rate prediction. In 1992, the UN estimated that world population would hit 10 billion by 2050. In more recent predictions, that milestone has been pushed back to the last decade of the 21st century.
The Spanish research was "published in the journal Simulation in February."