The causes of population change
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Population change is driven by four factors: births, deaths, immigration and emigration.
The first two determine the natural population change each year, namely the number of births minus the number of deaths. The second two determine net migration, which is the number of people moving into a population minus the number moving out to live elsewhere. The overall change in the size of a population is then the natural change plus net migration.
The chart shows population change in the UK in each year from 1922 to 2010. Natural change and net migration in each year are represented by lines, while the resulting overall population change is represented by bars. During this period, the UK population grew from 44m to 62m, with annual average growth of around 200,000 a year.
For much of the 20th century, population growth was driven largely by natural change. Where net migration had an effect it was often to reduce the growth caused by natural change through net emigration.
There were two periods when growth caused by natural change fell considerably: the first during the 1930s and the second during the 1970s. In the 1930s, this fall was offset to some extent by a period of net immigration. In the 1970s net migration remained negative, so population growth slowed to a halt and even briefly reversed.
Since the middle of the 1990s net migration has shown a consistent upward trend, and net immigration reached record levels in 2010. Natural change has also increased, and the UK’s fertility rate is now at its highest for almost 40 years.
Between 2010 and 2035 the UK population is projected to grow by around 11m, reaching 73m in 2035. Around 68% of this projected growth is expected to be due to net migration, either directly, through new migrants entering the population, or indirectly, through the birth of their children.
The chart shows annual population growth in the UK and what was driving it. From 1922-1963 net migration is estimated as the difference between total change and natural change.