US researchers reveal that up to 87 million people migrate every five years.
Over a five-year period, about one in 80 people around the world migrate to another country, researchers have revealed, in a study that shows more than a quarter of that movement is down to people returning to their country of birth.
Global migration is difficult to measure, with data often lacking for developing countries and inaccurate for others.
But a pair of researchers in the US say they have come up with a model that provides the most reliable “big picture” view of human migration yet. Crucially, they say, it takes into account the “churn” of people moving into and out of countries, something previous global estimates had not included.
“Policies that are set based on a quota of a number of people who enter the country miss out on the fact that you should also be expecting a lot of the existing migrant population to be leaving the country,” said Dr Jonathan Azose, a co-author of the study from the University of Washington.
The study, published in the journal PNAS, reveals a model for estimating migration around the world between 1990 and 2015, broken down into five-year chunks. The team say they were able to show the model worked by comparing its results with high-quality migration data from Europe.
A key problem with the previous leading global migration estimates, says Azose, is that the approach looked at overall changes in the net number of immigrants in a country over time, without taking into account that many individuals left and others arrived, resulting in underestimates of movement, something the new model tackles.
It suggests that between 67 million and 87 million people, including refugees, migrated for each five-year chunk – far higher than previous global estimates of 34m-46 m migrations – and corresponding to 1.13%-1.29% of the global population.
The team note that while absolute numbers of people migrating appear to have risen, there has been little change in the proportion of the world’s population who are on the move. That said, key origins and destinations change over time: for example,movement of Syrians in Saudi Arabia to Turkey between 2010 and 2015 were a leading contributor to “transit” migrations, while migration of Syrians from Syria to Turkey and Lebanon were among the largest emigration movements in that period.
The new study suggests that while migration to a new country makes up the biggest proportion of human movement, return migration – in which individuals return to their country of birth – accounted for between 26% and 31% of migration in each five-year period.
However, the team admit the new model has limitations, including the fact that different countries require individuals to stay there for different lengths of time to be registered as a migrant, and figures for the total number of migrants in each country might not be accurate to start with, meaning possible errors in the data used.
But the team say their work could help researchers delve deeper into what causes people to migrate and help them build predictive models for this.
Dr Nando Sigona, an expert in international migration and forced displacement at the University of Birmingham, who was not involved in the research, welcomed the study.
“Estimating migration flows is extremely difficult. Data are limited and incomplete, especially in less economically developed countries. This contributes to a perception in the west that all migration flows are directed towards the global north,” he said.
While the new model had limitations, he added, it offered a more rounded view of global migration, including showing movements between countries in the south and highlighting the large proportion of return journeys. “Finally,” he said, “it shows a world which is more dynamic and on the move than previously thought.”