The study projects:

The number of under-fives will fall from 681 million in 2017 to 401 million in 2100.

The number of over 80-year-olds will soar from 141 million in 2017 to 866 million in 2100.

Prof Murray adds: “It will create enormous social change. It makes me worried because I have an eight-year-old daughter and I wonder what the world will be like.”

Who pays tax in a massively aged world? Who pays for healthcare for the elderly? Who looks after the elderly? Will people still be able to retire from work?

“We need a soft landing,” argues Prof Murray.