Just over 200 years ago, there were fewer than a billion humans living on Earth. When I was born in 1960, there were three billion. In 2015, the human population has more than doubled to over seven billion people, and the UN projections expect that there will be ten billion humans on earth sometime towards the end of this century. This is if, optimistically, fertility rates continue to decline as they have done over the last fifty years. It is worth mentioning that this fifty-year decline in fertility rate, which many are keen to point out as a counter-claim to the argument that we have a problem, is actually slowing. It is also worth highlighting that if the current fertility rate were to continue unchanged (which the United Nations defines as the ‘constant fertility variant’), the global population at the end of this century would not be ten billion people, but will be twenty-eight billion.

With this in mind, I should point out that the UN population statistics have been systematically revised upwards over the past decade. The ‘peak’ population under the ‘expected scenario’ in 2100 was under ten billion. It is now over 11 billion according to estimates at the time of writing (Figure 8.1).