Stein Emil Vollset, the study’s lead author and Professor of Global Health at the Institute for Health Metrics and Evaluation (IHME), elaborated on the findings.

“The last time that global population declined was in the mid 14th century, due to the Black Plague,” he told IFLScience. “If our forecast is correct, it will be the first time population decline is driven by fertility decline, as opposed to events such as a pandemic or famine.”

Some countries, however, are forecasted to see an increase in population.