“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.”
Remarkably, the study also found that the population of specific countries could decrease by up to 50 per cent – included in that category are countries such as Italy, Portugal, South Korea, Spain, Thailand and Japan.
Vollset explained that much of this is to do with increased access to contraception and gender equality.
He said: “There are two key factors: improvements in access to modern contraception and the education of girls and women.
“These factors drive the fertility rate – the average number of children a woman delivers over her lifetime which is the largest determinant of population.
“The global total fertility rate is predicted to steadily decline, from 2.37 in 2017 to 1.66 in 2100, well below the minimum rate (2.1 live births per woman) considered necessary to maintain population numbers.”