The world population in 2050 will be decided by three billion women. If every second woman decides to have three rather than two children, the population will be 27 billion. The best guess is that, on average, women will have 2.1 children, the `fertility rate', and the population, will increase from 6 billion now to 10.8 billion. If, however, every second woman decides to have only one child instead of two, the world population will sink to 3.6 billion. Tiny changes in people's motivation result in huge changes to numbers, so there is a case for being sceptical about predictions. Many assumptions are made about people's motivation in deciding to have, or not to have, children, and obviously many forms of pressure and health aspects play their part. Education and health, for example, can be the most effective vehicles for reducing the growth of population. But demographers are also under pressure from politicians who like to hear that economic growth will restrain population, and from corporations who can use the scare of rising numbers to justify risky experiments with chemicals and genes.
Stable societies in the past, to some extent, had an understanding of `carrying capacity' -- the ability of their environment to sustain the desired quality of life over a long period. For example, the early colonisers of America had significantly larger families than their close relatives in crowded Europe. But improved agriculture and the technical aid programmes of the 20th century released families particularly in the South from this bondage and they felt confident in having more children, hence the population explosion. We face the paradox that the expectation of food security increased population but the number of hungry people is now greater than at any time in world history.
Human population increased very gradually over thousands of years. Then, following the industrial revolution, the rate of growth suddenly increased, particularly since 1950. But since the 1970s there has been a gradual reduction in the rate of growth in most parts of the world. The usual way of predicting numbers is to guess at fertility rates and assume that, since they have always increased in the past, they will continue to increase, though the recent slow-down will lead to a ceiling figure in due course.
But demographers also use the technique of fitting a mathematical equation to past trends. This has been done and shows a startlingly different outcome. The graph levels off in 20 years' time and then drops rapidly to pre-industrial levels. Demographers who favour the mathematical method point out that it is based on fact whereas the official approach is based purely on conjecture. The reducing populations of Italy, Japan and Russia may be the beginning of this trend. The burden of proof is therefore on those who predict continuing growth.
The mathematical approach presents a serious warning because it has affinity with current developments. Our plentiful supply of cheap energy is declining; low-lying cities may be flooded and agriculture threatened due to climate-change; ice-age aquifers are being exhausted; the `natural capital' of the world is reducing; past diseases return and new ones appear; ethnic conflict is increasing -- all point to a higher mortality rate. These tendencies, together with an ageing population and falling confidence in western culture, could provide feedback that reduces parents' perception of their future prospects, thus reducing the fertility rate. A reduced fertility rate and increased mortality could be the mechanism by which the mathematical prediction is confirmed.
So the surge of population during the last century may be a temporary phenomenon brought on by access to the cheap energy on which almost all our technology depends. In due course the human population may return to a level that is within the carrying capacity of the world.
Excerpted from The Little Earth Book by James Bruges, published by Alastair Sawday. To order a copy or for further details visit www.littleearth.co.uk