12.3 billion people by 2100: UN report

In its forecast for world population trends in the 21st century, a recently released UN study predicts that the main contributors of growth will be the sub-Saharan African countries. Above, a crowd descends on the beach at Durban, South Africa, on New Year's Day 2014. - Reuters

Already the most populous era in human history, the 21st century will be literally crawling with people.

Contrary to some earlier projections, the world’s population will soar through the end of the 21st century thanks largely to sub-Saharan Africa’s higher-than-expected birth rates, according to the United Nations and other population experts.