The world’s population will peak at 9 billion over the next 70 years before beginning a decline into the 22nd century, researchers predict in a new study.

Population currently stands at 6.1 billion, and the study projects that most of the new growth will continue to occur in developing countries. It also predicts some demographic changes. For example, the authors say, the number of people aged 60 or older will more than quadruple by 2100.