Carl Mortished: A shrinking population is the greatest threat to Earth

The good news — for sofa surfers, at least — is that Sir David Attenborough is fronting a new television documentary series. The less good news is that the new programmes, broadcast by Netflix, are unlikely truly to tackle the issue he really cares about: human fertility and the threat posed to our planet by rising human population.

That’s a missed opportunity because demographics is becoming the most exciting as well as troubling social science. It’s not just about why we need to protect wilderness from farming and urbanisation, so eloquently argued by Attenborough. It is about the global economy and how it may go in ever more surprising directions as regional human populations both expand and shrink.

Attenborough is a patron of Population Matters, a charity that campaigns for government efforts to arrest population growth. It was formerly the Optimum Population Trust and it acquired some notoriety for suggesting that a sustainable human population was about half its present level and arguing for curbs on child benefit. The charity is less strident today but its message is unchanged: we are too many.

But what if our numbers are shrinking? What if the main problem facing us will not be hordes of starving millions but a shortage of workers? In the developed world, human fertility is going negative. Women are giving birth to fewer babies than are necessary to replace the population — a rate of 2.05 per female. In the UK last year we were down to 1.7 births per female and, according to the Global Burden of Diseases study, published in The Lancet, fertility in 91 out of 195 countries was below replacement level. Average fertility in western Europe is 1.6 per female, in Canada and the US, it is 1.8. Central Europeans are down to 1.4 and the Japanese have almost given up; they are down to 1.3 births per female.

It’s all down to higher levels of female education, the decline of authoritarian religion and easy access to contraception. The affordability of mass entertainment gives people something else to do in the evening, such as watching wildlife programmes on telly. So you can guess which regions still experience higher birth rates: north Africa and the Middle East and sub-Saharan Africa. Fertility soars in areas of conflict: Afghanistan, 6.0 births per woman; Democratic Republic of the Congo, 5.1; Iraq, 3.8; Palestine, 3.5; Yemen, 4.5.

Yet there is hope because birth rates can change fast. Those who recall the panic about soaring populations in South Asia might be astonished to know that the birth rates are now static or even negative — Bangladesh 2.0 births per female and 2.1 in India.

China’s fertility rate is now 1.5 and many economists reckon the country has reached the Lewis turning point — when the supply of surplus rural labour reaches zero and creates rapid wage inflation. Chinese industry, which once relied on the vast unemployed hinterland to feed the assembly lines in Shanghai and Shenzhen, is now in a mad scramble to acquire skills in robotics and artificial intelligence.

The human population of Brazil, custodian of the Amazonian rain forest, can be expected to shrink in coming decades — its fertility rate is 1.8. That should be good news for those, like Attenborough, who worry about human incursion into its biological treasures. However, we should not see a rapid global shift from labour surplus to shortage as entirely benign. It may create economic turmoil, soaring wage inflation and, of course, the problem of even higher rates of human migration from regions of labour surplus to countries with a labour shortage.

If you want to know why Angela Merkel opened the door to a million migrants from Syria, Iraq and Turkey, you don’t need to ponder the German chancellor’s Lutheran heritage or Germany’s war guilt. Look no further than Germany’s birth rate, down to 1.4 per female. With an ever smaller body of young hands joining the workforce every year, the powerhouse of the European economy cannot sustain itself without a supply of immigrant labour and neither can the UK.

Training the long-term unemployed won’t do it. Employers want fit, bright and enthusiastic staff and if they are kept out by government diktat or a Trumpian wall, the choice may be an inflationary bust or the rapid replacement of labour by machine. The population crisis isn’t over, it’s just changing.