There is strong evidence that deteriorating environments caused by climate change are driving millions of people to resort to mass migration in their search for a better life, both within countries and across borders.

As temperatures rise these migrations will only increase, particularly in Latin America and India, which is predicted to overtake China as the country with the largest population by 2025.

An analysis of environment and migration, published in Nature Climate Change, of 30 studies of individual countries across the world shows that there is no one single factor that drives migration.

But most research has found that environmental hazards have a major influence. Rising temperature levels, changes in rainfall and single sudden events like hurricanes are all triggers.

Policies for improvement

The analysis, by the International Institute for Applied Systems Analysis (IIASA) in Austria and research partners across Europe, was undertaken to try to inform policy makers about how to avert mass human migration.

It points out that two of the most high-profile mass migration episodes in recent times – the Syrian refugee crisis in 2015 and the "migrant caravan" from Central America to the United States in 2018 – have been partly attributed to severe droughts in the countries concerned.

While some studies conclude that environmental factors were not the main driver of migration, most thought it was one of the primary causes. The analysis says governments should expect significantly higher migration flows in the future.

Perhaps surprisingly, given the publicity surrounding the issue, migrations were not centred on poor people trying to enter rich nations in Europe or North America. Instead, most movements were from the countryside to urban areas in the same country, particularly in agriculturally dependent countries, or from one middle-income country to another.

People with particularly low incomes normally stayed where they were, despite environmental pressures, because they had no way of financing a move, while richer people had the means to adapt to new circumstances and so they also stayed put.

"Environmental factors can drive migration, but the size of the effects depends on the particular economic and socio-political conditions in the countries," explains the lead author Roman Hoffmann, from Germany’s Potsdam Institute for Climate Impact Research (PIK).

"In both low and high income countries, environmental impacts on migration are weaker – presumably because either people are too poor to leave and therefore essentially become trapped or, in wealthy countries, they have enough financial means to absorb the consequences. It is mainly in middle-income regions and those with a dependency on agriculture that we see strong effects."

IIASA predicts future higher levels of environmental migration for countries in Central America, the Caribbean, Brazil and Argentina. In Africa it is the Sahel region south of the Sahara that is already drying out, and East Africa that has the highest potential for people migrating because of climate change.

Eyes on India

Perhaps the most disturbing prediction is that India, with 1.3 billion people and soon to be the most populous country in the world, is likely to see large migrations. The heat and floods in the country are already killing hundreds of people a year, and many millions who are still dependent on subsistence agriculture are struggling with changing climate conditions.

"Our research suggests that populations in Latin America and the Caribbean, several countries in sub-Saharan Africa – especially in the Sahel region and East Africa – as well as western, southern and south-east Asia, are particularly at risk," says co-author Anna Dimitrova from the Vienna Institute of Demography of the Austrian Academy of Sciences.

While the report is aimed at preparing governments for migrations that will inevitably happen in the future, with difficult consequences for both the migrants and the host country, the research suggests the best way of averting the coming crisis is to tackle climate change and reduce further rises in temperatures.

"The best way to protect those affected is to stabilise the global climate by rapidly reducing greenhouse gas emissions from burning fossil fuels as well as simultaneously to enhance adaptive capacity, such as through improving human capital," says Jesus Crespo Cuaresma, a researcher with the IIASA World Population Program and professor of economics at the Vienna University of Economics and Business.