Earth’s population may start to fall from 2040. Does it matter?

William Reville: As populations age and are not replenished, societies could be strained

The conventional projection by the UN is that world population, currently 7.7 billion, will increase to 11.2 billion in 2100, then stabilise before slowly declining. However, current trends cast much doubt on this picture. Fertility rates are in dramatic decline worldwide and world population may peak below nine billion by 2050 and then decline.

In order for a human population to maintain its numbers, each woman must bear, on average, 2.1 children. If the birth rate exceeds 2.1, population numbers increase; if it is less than 2.1, population numbers decline. Birth rates below 2.1 have been common now since 1970. Ireland had a birth rate of 1.92 in 2016 but inward migration is contributing to population growth.

The UN World Fertility Patterns 2015 Report details birth rates (children per woman) for the major world regions – Africa 4.7, Asia 2.2, Europe 1.6, Latin America/Caribbean 2.2, North America 1.9, Oceania 2.4. The overall world fertility rate is 2.5. So world population numbers continue to grow.

World population trends were reviewed recently by Darrell Bricker and John Ibbitson in the Observer on January 27th. The authors seriously questioned the UN projection that world population numbers would continue to increase until 2100, quoting several well-respected demographers. Jorgen Randers, a Norwegian academic who decades ago warned of a potential global catastrophe caused by overpopulation, has changed his mind.


"The world population will never reach nine billion people," he now believes, "It will peak at eight billion in 2040 and then decline." Similarly, Prof Wolfgang Lutz and his fellow demographers at Vienna's International Institute for Applied Systems Analysis predict the human population will stabilise by mid-century and then start to go down.

European decline

The populations of many countries shrink every year. For example, Japan's dropped 450,000 in 2018. Many of the fastest-shrinking populations are in eastern Europe. The following countries are examples where populations are in decline (fertility rates in brackets, but population decline is often increased by emigration) – Bulgaria (1.58), Greece (1.3), Hungary (1.39), Italy (1.49), Poland (1.29), Portugal (1.24), Russia (1.75), Japan (1.48) and South Korea (1.26).

Declining fertility rates, combined with increasing life expectancy, generate societies enriched in older people and depleted in younger people. This strains society’s ability to generate the wealth and taxes necessary to fund the welfare state and healthcare for the elderly.

India, with a fertility rate of 2.1, will soon overtake China as the world's most populous nation

There are several reasons why birth rates have plummeted in the developed world. For example, full-time careers are now the norm for women. I come from a family of five children and my mother worked full time in the home. Both my wife and I have always worked careers and we have two children. People also tend to have fewer children now because of better healthcare – every child born is expected to survive. And, of course, contraception is universally available nowadays.

Declining birth rates are no longer confined to the western world. Birth-rate decline in large countries of the developing world is dramatic. China has a fertility rate of 1.5 and is the world's most populous country. India, with a fertility rate of 2.1, will soon overtake China as the world's most populous nation. Brazil, the fifth most populous country, has a fertility rate of 1.8.


Why are fertility rates declining so dramatically in the developing world? The Observer article identifies urbanisation as one important driver. In 2007, for the first time ever, the majority of the global population lived in cities. Sixty-six per cent of the global population will live in cities within 30 years.

When women move from rural to city life, many things change that reduce birth rates. In the countryside a child can help by working on the land, but in a city a child is an economic liability. Also, cultural pressures to have more children recede in cities while access to media, schools and contraception increase.

Africa has the highest fertility rates in the world, accounting for most of the world’s population growth. Unfortunately, Africa is also the world region presently worst-equipped to cater for burgeoning population numbers. But, birth rates are starting to fall, urbanisation is afoot and Africa already has a plentiful supply of young people, an essential resource to work a modern economy. Africa could well become an emerging China as this century progresses.

William Reville is an emeritus professor of biochemistry at UCC