**This is the first of a few posts on population growth and climate change.**
For the human population to not decline you basically need each woman to, on average, produce more than two babies. In rich countries the figure needed is about 2.1, in poorer countries it’s a lot higher, for the simple reason that children are much less likely to reach reproductive age. In technical terms this is referred to as replacement level fertility, go above and population will increase in the long term, go below it then population will decline in the long term. Of course this only refers to the indigenous population. Population increases due to immigration can offset this.
How much does the average number of children per woman vary by country? The graph below shows average number of children per woman versus population in every country on earth in 2010. (I have logged the population axis because India and China skew it)
Surprisingly, there are 79 countries that average less than 2.1 children per women.
Which countries are these? Below I have plotted a word cloud of all of these countries.
Many of these are developed countries, which have gone through what is called the demographic transition. Exactly why birth rate is so slow is something of a mystery. In blunt Darwinian terms you wouldn’t expect women to lack fecundity when they are wealthy.
There are some surprises here. Iran averages just under 1.7 births per woman. Italian women, it would appear, do not listen too closely to advice of the Vatican. They average just over 1.4 births per woman. China’s one child policy has also put it on the list, with an average of 1.6 births per woman. Who is the lowest? Taiwan with 0.9 children per woman, though they recently boosted this a little bit.
We are also looking at a very heft chunk of humanity. Adding up the populations of all of these countries and we get a total of 3.3 billion. A simple lesson here is that when we are looking at the environmental impact of population growth it is not really a good idea to look simply at the global population. Countries vary massively in how much their population is growing, and by how much their citizens impact on the environment, in particular their carbon emissions.
(All of the data used here are taken from the excellent Gapminder website.
For the statistically inclined,the wordcloud was made using the R package “wordcloud” )