Published online 26 July 2010 | Nature | doi:10.1038/news.2010.375

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Mexican 'climate migrants' predicted to flood US

A tenth of Mexico's population could surge north to escape climate-triggered crop failures, study claims.

Mexican maize farmerIf climate change worsens drought in Mexico, crops could fail and people be forced to migrate, says a new study.Bao Feifei/Xinhua/Photoshot

A wave of up to 6.7 million migrants from Mexico could head to the United States to escape the ravages of climate change on crops, say the authors of a new study. The findings are claimed to be the first to thoroughly quantify how shifts in global climate might affect human migration from one region to another.

The study's authors, from Princeton University in New Jersey, say the United States should prepare for the arrival of up to 10% of Mexico's adult population over the next 70 years as a result of falling agricultural productivity due to climate change.

According to the Pew Hispanic Centre in Washington D.C., there were 12.7 million Mexican immigrants in the United States in 2008.

But the study has also provoked ire from immigrant-rights advocates, who say the findings could be used to advance anti-immigration causes. In the United States, Mexican immigration is a contentious issue, and tough new immigration laws in Arizona, which borders Mexico, have sparked national debate in recent months.

The latest study is likely to fan the flames, as it warns of exacerbated environmental, economic and social problems that unmanaged and unexpected climate-related migration could bring to both the United States and Mexico.

"It would behoove them as scientists to shift their focus," says Lorenzo Cano, associate director of the Center for Mexican American Studies at the University of Houston in Texas, who is an activist for immigrants' rights. "[This is] research that will contribute to the xenophobia that is already running amok in our country today."

Down on the farm

Publishing in Proceedings of the National Academy of Sciences,1 environmental scientist Michael Oppenheimer and economist colleagues set out to develop a model that quantitatively predicts the potential size of the problem of mass human migration spurred by climate change. The team focused on cross-border migration from Mexico to the United States as an example.

Applying standard statistical techniques common in economics, they used Mexican state census data to infer the flow of emigration. They then correlated this with data on how changes in climate had affected maize (corn) and wheat productivity in different Mexican states during the same time. In this way, they estimated the sensitivity of Mexican emigration to alterations in crop yields due to climate change.

The resulting figure — that a 10% reduction in crop yields leads to an additional 2% of the population emigrating — was then applied to what might happen under the scenario proposed for 2080 by the Intergovernmental Panel on Climate Change (IPCC), in which levels of atmospheric carbon dioxide have stabilized at 555 parts per million, and global temperatures are 1–3 °C above recent temperatures.

Keeping other variables constant, the authors modelled the results for a series of different levels of agricultural adaptation that Mexican farmers might undertake to mitigate the effects of climate change.

In the worst-case scenario of no adaptation, crop yields dropped by 48%; in the best-case scenario, with major adaptations, crop yields fell by 10%. The authors estimate that this would spur the emigration to the United States of between 1.4 million and 6.7 million adult Mexicans (or 2–10% of Mexico's current adult population).

"This is obviously just the opening gun [for the model]," says Oppenheimer. "We want people to be looking at other border regions to build up a global picture."

He said the team had thought hard about how their results might be used before undertaking the work. They decided that it was better to provide the information, which would be "of interest" to policy-makers, and to do their best to ensure that it was not used for the wrong purpose.

Baseline facts

"We certainly don't want these results to be misused as another hammer against immigrants," Oppenheimer says, adding that the team is not making value judgements or specific policy recommendations, but simply trying to determine the "baseline facts" so that policy-makers can decide what to do.

But others disagree, saying that it is wrong to make Mexican immigration to the United States the focus of the climate-change problem and that the study lacks context.

"Mexican migration is part of the solution to many of the current [US] labour market demands," says Cano. "The scientific community should explain this within the context of any studies focusing on the impact of climate change."

Bob Dane, a spokesman for the Federation for American Immigration Reform, an anti-immigration group, says the group did not consider that "bad news" was "good news" for its cause, but that the study highlights a serious problem. "This could be yet another area that Mexico neglects," he adds.

Others identify assumptions in the study that could mean the predicted size of the immigration flow is too large.

Neil Adger, an expert on climate-change adaptation at the University of East Anglia in Norwich, UK, who is evaluating human migration issues for the next IPCC report, says the study does not consider the possibility that crop yields in the United States could also be drastically reduced by climate change. "This would reduce the demand for labour and dampen the flows suggested," he says.

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Douglas Massey, a sociologist at Princeton, says that he thinks some of the migration attributed by the study to environmental change could actually be the result of structural changes in the Mexican economy. "Over the same period of the study [1995–2005], Mexico's economy underwent a wrenching change as agricultural subsidies were ended, price supports eliminated, and communal lands privatized," he says.

And both researchers caution that the Mexico-US example is unique. The two countries see one of the largest cross-border flows of people anywhere, and generalizing the results to any exodus of people from other developing countries would be problematic.

Oppenheimer says he now intends to look at climate-induced displacement, or internal migration, in the United States, and will possibly tackle US immigration to Canada in the future. 

  • References

    1. Feng, S., Krueger, A. B. & Oppenheimer, M. Proc. Natl Acad. Sci. USA doi:10.1073/pnas.1002632107 (2010).

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  • #61163

    I think if the world’s population were built at Brooklyn density, it would occupy about 70% of the state of Texas. At Manhattan densities, you could fit the whole world into Virginia and North Carolina, leaving the rest of the world empty to grow crops.

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