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A rice farmer walks through a field near Tegalang in Indonesia. Economic losses tied to weather may be increasing migration.


Global Warming a Significant Driver of Farmer Migration, Study Finds

Climate change will outweigh natural disasters in spurring permanent migration of poor farmers.

A warming world is causing more farmers to permanently relocate, suggests a survey released on Monday that focused on migration in Indonesia.

Among Indonesian farmers, warmer temperatures are a more important motivation for migration than are volcanoes, earthquakes, and other natural disasters common in the island nation, according to a study published Monday in the Proceedings of the National Academy of Sciences. (Related: "Volcanoes Cover Indonesian Cities With Ash.")

As islands shrink, deserts grow, and monsoon patterns shift, global warming is expected to trigger migrations worldwide. The new study tracked 7,185 Indonesian households over four years and found that economic losses tied to weather seem to increase migration.

"Of all the environmental factors, temperature had the most significant effect on migration," according to the study, led by Princeton University's Pratikshya Bohra-Mishra. Increased rainfall, also related to global warming, played a role in stimulating migration as well.

Overall, the team found that temperatures above 77 degrees Fahrenheit (25 degrees Celsius) marked a "turning point" at which migration to cooler places began to increase. The rate roughly doubled with each 1.8 degree Fahrenheit (1 degree Celsius) temperature increase above that mark.

Indonesia is the planet's fourth most populous nation, and most of its people work on farms. Migration triggered by floods, earthquakes, and volcanoes was minor or negligible among the households.

Over this century, Indonesia is projected to see a temperature increase of 3.6 to 4.5 degrees Fahrenheit (2 to 2.5 degrees Celsius), according to climate models. In some Indonesian provinces, this will drive as much as 5 percent of the local population to migrate, while in others, temperatures will not reach a turning point and migration won't be affected, the study finds.

The results point to the need to look at climate impacts on the local level, the researchers conclude, including in the U.S. corn belt, which is projected to see heavy losses in farms and farmers as the climate warms.

In California, meanwhile, a long-running drought has farmers worried about the future of that water-dependent state.

"Crops will change ... We are the leading agricultural zone in North America," said historian Kevin Starr of the University of Southern California, author of California: A History. "You will see a lot of localized solutions converge if the drought lasts long enough."

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Susan Goldberg contributed reporting to this story.