A new generation in South Africa (Image: Henk Badenhorst/Getty)

There may not be a let-up after all. The human population is unlikely to stop growing this century as expected, according to new projections. That could add to the pressure on the environment and accelerate climate change.

The research concludes that the population of Africa will grow much faster than expected, overwhelming the slower growth and even declines in other regions. But it is an overly pessimistic conclusion that flies in the face of other analyses, critics argue.

The general consensus is that the rapid growth in the human population will slow over the next few decades and level off well before the end of the century. “Projections up to about 10 years ago projected world population to keep growing to about 9 billion in 2050, and then to level off or decline,” says Adrian Raftery of the University of Washington in Seattle. “But our results suggest this levelling off is unlikely.”


Instead, Raftery and his colleagues have estimated that the world population will soar from the current figure of 7.2 billion to between 9.6 and 12.3 billion by 2100.

Africa boom

“The biggest difference between our results and the older projections is that ours expect a large increase in the population of Africa, from the current 1 billion to more than 4 billion in 2100, with a lower bound of 3.5 billion,” says Raftery.

Fertility rates in Africa have fallen from their peak of 6.5 children per woman, thanks to greater prosperity and better conditions for women. But Raftery says they have levelled off at around 4.6 instead of continuing to drop as expected. The main reasons are better survival from HIV – which often kills mothers and their babies – and lack of available contraception, the researchers say.

For example, in the continent’s most populous country, Nigeria, the United Nations predicts the population will decline. But the stalled decline in fertility means that instead the population could soar from 160 to 914 million by 2100, says Raftery.

His team has also calculated the probabilities that particular population scenarios will materialise, which has not previously been done. They estimate that the likelihood of the global population stabilising by 2100 is only 30 per cent.

Education is key

The new growth predictions are drawing criticism. “Raftery’s projections are too high for Africa, because they don’t include the fact that female education is the key driver of fertility decline,” says Wolfgang Lutz of the International Institute for Applied Systems Analysis in Laxenburg, Austria. For example, in Ghana, women with no education average 5.7 children, while those with junior and secondary education have 3.2 and those with post-secondary education just 1.5.

Lutz has just published his own population analysis, which suggests that more education of women will eventually cause African fertility rates to decline as expected (Population and Development Review, DOI: 10.1111/j.1728-4457.2014.00696.x).

However, Lutz and Raftery agree on how to stem the population surge: “The two policies known to have an effect are increased access to contraception and increased education for women,” says Raftery. Lutz agrees: “These are the key to bringing down fertility rates in Africa, in addition to leading to better health and economic growth.”

For now at least, the threat to the environment of population growth in Africa is not as severe as might be expected, because each will consume few resources compared with people in rich countries.

“In the short to medium term, population growth in Africa will have less impact than the same growth in higher-consumption countries,” says Raftery. But he says Africa’s economy is growing, so consumption there could eventually become a problem, too.

Journal reference: Science, DOI: 10.1126/science.1257469