This week the United Nations produced a new forecast for the global population. The Department of Economic and Social Affairs issued the last one in 2019. COVID had delayed the normal 2 year cycle. The media duly featured the highlights of the new report and the UN commentary. What they did not do was to compare the two forecasts to understand the differences.
Any forecast of population relies on assumptions about three underlying factors. The first two are the number of people dying and the number of babies being born. The third is migration. When forecasting a global population, migration is not an issue!! Mortality tends to be the more predictable of the two. Increasing longevity can push back death and complicate the forecasts. Despite this the mortality trends are pretty stable. Forecasts of births is much more complex. Fertility, or the number of children a female has in their life time, is falling all over the world. The margin for error is higher
There are different ways to do a forecast. The UN forecast is an extrapolation of trend lines. The Washington University forecast, by comparison, is based on building more complex models. Their fertility is forecast based on two variables. They use "the education of women" and "the availability of contraception in any given geography". Beginning in 2017 the UN constrained its fertility forecast. They believe that the long run fertility will be around 1.7 births per female. This will be consistent across countries. Below the replacement level of 2.1 children per female some countries have shown such a stabilization of fertility. For other countries the downward trend has continued. Taiwan currently has the lowest fertility at 1.1 children per female. That assumption was carried over in to the 2019 and 2022 forecasts.
Without looking at forecasts we can look at the changes in the underlying data. The global population has increased from 7.7Bn in 2019 to 8.0Bn predicted for 15 November 2022. Life expectancy in 2019 was 72.8 years. There is a huge variation across countries with poorer countries having higher mortality. The biggest cause is still the high mortality amongst children and their mothers. In 2019 9% of the worlds population was over 65. This had risen to nearly 10% by 2022. The period is very short for any changes in mortality and longevity to be visible.
In 2019 27 countries were facing a “population decline of greater than 1%”.” Close to fifty percent of the world’s population lived in a country were the birth rate is below replacement level”. The global average fertility was 2.5 having fallen from 3.2 births in 1990. By 2022 the global fertility had fallen to 2.3. This may not seem much but it is close to a ten percent change in three years. By 2022 " Two thirds of the worlds population now lives in countries with a population below replacement level" . This is a huge increase in only three years.
At first sight the global forecasts have not change much. The best estimates are that” the global population will be 8.5BN in 2030, 9.7Bn in 2050 and 10.4BN in 2100”. This growth rate was the lowest since 1950. It is forecast to be less than 1%, These forecasts are almost identical to those 2019 for those dates. For example the 2019 forecast for the turn of the century was 10.9bn. 0.5Bn is a lot but we are forecasting out seventy years.
What the report does not highlight is the major difference in the assumptions of the shape of that growth. The UN now forecasts that the population will peak some time in the mid 2080’s and will then plateau. In 2019 it had considered such a scenario. It had only given a 27% chance to the population peaking this century. It had a higher probability of it happening in the first half of the next century. They have cut the time to “peak population” in half.
The population of 61 countries is now forecast to be declining by more than 1% by 2050. Countries such as Bulgaria, Latvia, Lithuania , Serbia and The Ukraine are expect to suffer a population decline of more than 20% .
The Greying of the World
Those populations are ageing as well. The proportion of over 65’s in the global population is forecast to reach 12% in 2030, and 16% by 2050. That hides huge variations. Europe and North America will have over 26.9% of their population in that age group. In Eastern and South-Eastern Asia (predominantly China, Japan and Korea) over a quarter of the population will be over 65. Australia and New Zealand will be at the same level.
The UN Forecasts are essential benchmarks. They are used to assess the Strategic Development Goals. They are also the basis of fund allocations. The 2022 Forecast contains some significant changes. “Peak Population” will be a symbolic moment. To bring it fifty years closer is a major shift. To do so whilst maintained an assumption of a long term fertility level that is around 1.7 is even more symbolic. The current forecasts assume an increase in fertility in two regions. The first is Europe and the USA which is forecast to increase from 1.5 today to 1.6 by 2050. The UN forecasts that fertility will rise from 1.5 to 1.6 in Eastern and South-Eastern Asia.
The UN argues that such increases are consistent with gender equality. They cite surveys that people are having less children than they desire. Conversely they also list the many constraints on bigger families. These include childcare, higher education and ageing parents. They point out the biological limits to pregnancy. Their proposal is that these constraints “need addressing”.
To remove the long term “target” would be to change the forecast significantly . The newest forecast came from the Institute of Health Metrics and Evaluation at the University of Washington. Their best estimate forecast shows global population peaking twenty years earlier. By the mid- 2060’s they forecast a peak and then a decline not a plateau. World population by the turn of the century would be back to today’s levels. The difference is in their fertility forecasts particularly those below replacement level. They redid the UN forecasts. They extrapolated all countries to allow them to continue following their trend line decline in fertility. The result was close to their own forecast.
The jury is out, but this is an important competition. Global warming, food and water strategy all depend on a global population forecast.