To start the New Year, let’s have a look at the difficulty of predicting global population growth deep into the 21st century. This is important to remember when we consider what policies should be adopted based upon population predictions for decades away.  In short, trying to figure out what population a country or the world will have and which countries will grow and which will shrink is a tricky business. And this is not surprising when we consider the intensely personal nature of a couple’s decision to have a child and the myriad of factors that go into that decision: financial, religious, chance.  And of course that is just thinking about children that are planned by their parents.  Thus, we must be careful when we think and talk about population predictions and the policies crafted to deal with these predictions. (Particularly when those policies involve enforced sterilisation or abortion – as we see in China.)

With that in mind, researchers at the Worldwatch Institute have looked at some recent demographic projections for the 21st century. As Senior Fellow Robert Engelman and Research Assistant Yeneneh Terefe write, the United Nations Population Division and the International Institute for Applied Systems Analysis (IIASA) have agreed on how the world’s population has grown until now.  However, the two now disagree as to how the population will grow in the future.

“U.N. demographers rely on a methodology that applies past behavior and expert opinion about the future to assign quantified probabilities to various population outcomes. Defying a widespread media and public perception that a stationary world population of 9 billion in 2050 is a near certainty, the U.N. analysts report that the most likely long-term future is for continued growth into the 22nd century.

Demographers associated with IIASA, based in Laxenburg, Austria, however, differ with this analysis. They foresee world population peaking around 2070 at 9.4 billion people and then gradually shrinking to 8.9 billion by the century’s end.”

The reason why the two institutions disagree is due to the assumptions that they make.  In short, the UN relies heavily on recent surveys that show that the average number of children that women are having in their lifetime is not falling in countries that earlier projections had assumed that they would. In contrast:

“The IIASA demographers…focus largely on educational trends. In every region of the world, including Africa, the proportion of young people enrolled in school has generally been rising, and these rates are likely to continue to rise, the analysts argue. Because even moderately high levels of educational attainment are associated with reductions in fertility, fertility even in high-fertility countries is likely to fall more than current fertility trends on their own suggest, the demographers reason.”

But this shows that predictions of continued global demographic growth are not certain. The worry that our population is going to continue to grow (particularly in Africa) is not “settled” – not even in the way that the climate change science is “settled”.

For a bit more of an outlandish prediction (hopefully!) is that by two Australian environmental scientists, Corey J. A. Bradshaw and Barry W. Brook, who added scenarios in which humanity experiences some global catastrophe.  In their most extreme scenario, 6 billion people die in the early 2040s, in which case human population would decline to about 5 billion by 2100. Let us hope it does not come to that! Anyway, as we continue to write blogs about the world’s population trends in 2015 (and you continue to read them – please!) we must take all future predictions with a grain of salt. Predictions are just that: predictions. Nothing is certain and we can only make educated guesses.

Marcus Roberts is a Senior Researcher at the Maxim Institute in Auckland, New Zealand, and was co-editor of the former MercatorNet blog, Demography is Destiny. Marcus has a background in the law, both...