Extreme weather is contributing to undocumented migration and turn-backs between Mexico and the United States, suggesting more immigrants may risk their lives crossing the border as climate change fuels droughts, storms and other hardships, according to a new study.

People in agricultural areas of Mexico were more likely to cross the border illegally after droughts and were less likely to return to their original communities when extreme weather continued, according to research this week in the journal Proceedings of the National Academy of Sciences.

Across the globe, climate change – caused by the burning of fossil fuels such as coal and natural gas – is exacerbating extreme weather. Droughts are longer and drier, the heat is deadlier and storms are rapidly intensifying and dumping record rainfall.

In Mexico, a country of nearly 130 million people, the drought has dried up reservoirs, created severe water shortages and drastically reduced corn production, threatening livelihoods.

The researchers said Mexico is a notable country for studying the links between migration, return and weather stressors. The average annual temperature is projected to rise as much as 5.4 degrees Fahrenheit by 2060, and extreme weather is likely to economically devastate rural communities dependent on rainfed agriculture. The US and Mexico also have the largest international migration flow in the world.

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Scientists predict that migration will increase as the planet gets hotter. Over the next 30 years, 143 million people worldwide will be uprooted by rising seas, drought, extreme temperatures and other climate catastrophes, according to a report by the UN Intergovernmental Panel on Climate Change.

The new migration research comes as Republican Donald Trump was re-elected to the US presidency this week. Trump has called climate change a “hoax” and promised mass deportations of an estimated 11 million people in the US illegally.

The researchers said their findings highlight how extreme weather drives migration.

Filiz Garip, study researcher and professor of sociology and international affairs at Princeton University, said advanced nations have contributed much more to climate change than developing countries that bear the brunt.

Migration “is not a decision that people make lightly … and yet they are forced to make it more and they are forced to stay longer in the United States” as a result of extreme weather conditions, Garip said.

The researchers analyzed daily weather data along with survey responses from 48,313 people between 1992 and 2018, focusing on about 3,700 people who crossed the border without documents for the first time.

They analyzed 84 farming communities in Mexico where corn cultivation depended on the weather. They correlated a person’s decision to migrate and then return with abnormal changes in temperature and precipitation in their home communities during the corn-growing season from May to August.

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The study found that communities experiencing drought had higher migration rates compared to communities with normal rainfall. And people were less likely to return to Mexico from the US when their communities were unusually dry or wet. This was true for recent arrivals from the US and for people who had been there longer.

People who were better off financially were also more likely to migrate. So were people in communities with established migration histories, where friends, neighbors or family members who had previously migrated could provide information and help.

These social and economic factors influencing migration are well understood, but Garip said the study’s findings underscore the inequities of climate adaptation. With extreme weather events, not everyone is affected or reacts in the same way, she said, “and typical social and economic advantages or disadvantages also shape how people experience these events.”

For Kerilyn Schewel, co-director of Duke University’s Program on Climate, Resilience and Mobility, economic factors highlight that some of the most vulnerable people are not those displaced by climate extremes, but rather “trapped or under-resourced.” necessary to move”. .”

Schewel, who was not involved in the study, said that analyzing regions with migration histories could help predict where migrants will come from and who is more likely to migrate due to climate shocks. In “places where people are already leaving, where there is a high prevalence of migration, … that’s where we can expect more people to leave in the future,” she said.

The survey data used from the Mexican Migration Project makes this study unique, according to Hélène Benveniste, a professor in Stanford University’s Department of Environmental Social Sciences. Migration data on its scale, which is community-specific, is “rarely available,” she said in an email. So is information about a person’s complete migration journey, including their return.

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The finding that return migration decisions were delayed by weather stress in home communities is “important and novel,” said Benveniste, who studies climate-related human migration and was not involved in the study. “Few datasets allow an analysis of this question.”

But increased surveillance and enforcement along the U.S.-Mexico border makes returning home — and moving back and forth — more difficult, said Michael Méndez, assistant professor of environmental policy and planning at the University of California, Irvine. And once undocumented migrants are in the U.S., they often live in dilapidated housing, lack health care or work in industries like construction or agriculture that make them vulnerable to other climate impacts, he said. Méndez was not involved in the study.

As climate change threatens social, political and economic stability around the world, experts said the study underscores the need for global collaboration around migration and climate resilience.

“So much of our focus has kind of been on the border and securing the border,” Duke’s Schewel said. “But we need much more attention not only to why people leave, but also to the demand for immigrant workers in the US.”