The population of the world, long expected to stabilize just above 9 billion in the middle of the century, will instead keep growing and may hit 10.1 billion by the year 2100, the United Nations projected in a report released Tuesday.

Growth in Africa remains so high that the population there could more than triple in this century, rising from today’s one billion to 3.6 billion, the report said — a sobering forecast for a continent already struggling to provide food and water for its people.

The new report comes just ahead of a demographic milestone, with the world population expected to pass 7 billion in late October, only a dozen years after it surpassed 6 billion. Demographers called the new projections a reminder that a problem that helped define global politics in the 20th century, the population explosion, is far from solved in the 21st.

“Every billion more people makes life more difficult for everybody — it’s as simple as that,” said John Bongaarts, a demographer at the Population Council, a research group in New York. “Is it the end of the world? No. Can we feed 10 billion people? Probably. But we obviously would be better off with a smaller population.”