For every 10 percent of lost crop yields, 2 percent more Mexicans will leave and most will try to come to the United States, Michael Oppenheimer of Princeton University in New Jersey and colleagues predicted.
The study touches on two extremely sensitive U.S. political issues — immigration and climate change.
“It has been well established that farmers do tend to want to migrate when they are not doing so well,” Oppenheimer said in a telephone interview.
Oppenheimer’s team looked at Mexican census data from 1995 to 2005, along with statistics on crop production and climate data. “We lined up the climate changes, the crop production changes ... with the census data, which allowed us to infer the emigration rate,” he said.
“Climate change is expected to cause mass human migration, including immigration across international borders,” Oppenheimer and his team wrote in the Proceedings of the National Academy of Sciences.
By the year 2080, they projected, between 1.4 million and 6.7 million Mexican adults will emigrate as a result of reduced farm productivity.
“Although the results cannot be mechanically extrapolated to other areas and time periods, our findings are significant from a global perspective given that many regions, especially developing countries, are expected to experience significant declines in agricultural yields as a result of projected warming,” they wrote.
“Indeed it looks like the climate change could be an important factor in future migration,” said Oppenheimer, a member of the Intergovernmental Panel on Climate Change. “It underscores the need to grapple with greenhouse gases.”
Oppenheimer stressed that the study did not address the cause of the variation in climate that affected Mexican crops. He also said it did not look at whether the migrants moved to the United States legally.
On Thursday, a tough new immigration law takes effect in Arizona, which borders Mexico. It requires law enforcement officials to check the immigration status of anyone they suspect may be in the United States illegally, but it is being challenged in court by the White House.
Of the 11 million illegal immigrants believed to be living in the United States, about 6.7 million are from Mexico.
Data show the world is getting warmer and many studies show human activity is contributing to the trend. Warmer weather can hurt crops by creating droughts, stronger storms and flooding.
The Earth Institute at Columbia University in New York says that 2000-2009 was the warmest decade on record. Earth’s climate has warmed 0.8 degree C (1.5 degrees F) on average since modern records have been kept, and June was the warmest ever recorded.
“We chose Mexico for our study because it is one of the biggest migrant-source countries, because there exists state-level data on emigration, and because it has undergone diverse degrees of climate variability across regions,” Oppenheimer’s team wrote.
“Yet, to our knowledge, no study has directly associated a component of the increase in emigration with changes in climate, despite numerous reports and anecdotes of Mexican farmers fleeing to the United States because they no longer could maintain their previous way of life because of climate-driven crop failures.”
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