The key question: Does this probabilistic approach increase the accuracy of our long-term perspective on population? The short answer: no. The basic trouble with all long-range population projections is that they are driven by assumptions about birth levels—and there is still no reliable method for predicting fertility levels a generation from now, to say nothing of a century hence. Demographers are even hard-pressed to explain historical fertility patterns.

Half a century ago, in the early 1960s, East Asia's overall fertility level was about 5.5 births per woman; today, according to the U.N. Population Division, it is about 1.6 per woman—70% lower. In scope, scale and speed, nothing like this decline had happened in human history. Bayesian projections would never have regarded that outcome as likely, just as they would have most likely missed the startling 70% drop in fertility in Iran between the early 1980s and early 2000s. The main reason behind the newly reported higher world population projections is unexpected continuing higher fertility in sub-Saharan Africa. The median number of children per woman is 4.6, above the replacement level of 2.1 which would result in population stabilisation.  Since 1970, a global decline in fertility has occurred across most of the world. In the United States, and much of the West, fertility is now actually below replacement level.  So will Africa’s fertility remain high in the future despite trends in the West?  The Wall Street Journal considers the following variables:

In 2000 a third of Africa's women of childbearing age (15-49) had a high-school education or better; researchers at the International Institute for Applied Systems Analysis in Vienna anticipate that by 2050 the figure will be 70%. Also around 2050, the U.N. Population Division projects that life expectancy at birth will average nearly 70 for the sub-Saharan region, up almost a decade and a half from today.

If such changes come to pass—changes that have corresponded with lower birth rates elsewhere in the world—would Africa still remain resistant to fertility decline? Some would reply that cultural tradition and related factors will continue to support high fertility rates, and those voices may ultimately be right. But that same argument was [wrongly] made about the greater Middle East not so long ago. Finally, as always the West forgets that they are the main consumers of the Earth’s resources – not the African people who consume far, far less per person.  So perhaps we should look at our own consumption before we turn to the African people to tell them they shouldn’t have the choice to have 4 children (and research has shown that this is indeed a choice for many African women, rather than a lack of contraception which is so often assumed).  The West is spending more and more on air travel, more powerful cars, multiple household appliances which are replaced rather than fixed, electronic devices that are practically made to break after a couple of years when they will surely be obsolete anyway and touchscreens which require rare earth minerals mined from the earth or the ocean floor. People also waste a huge amount of food. You may like to re-visit Mercatornet’s Top 10 Eco-villians. The bottom line is to remember to look beyond the headlines to the assumptions and biases which lie beneath.