When experts warn of the consequences of global climate change, they usually cite impacts on natural systems. They tell us that ice caps will melt, sea levels will rise, extreme weather will become more common, droughts will increase in frequency, oceans will become more acidic and so on.
In recent years, we have also come to discuss the broader, indirect effects of climate change on our societies, economies and political systems. National security, for instance, will face a variety of new challenges as temperatures rise. Experts anticipate increased conflict over scarce resources, competition for access to new maritime passageways, more flooding and, in response to these and other crises, increased migration.
In a recent study published in the Proceedings of the National Academy of Sciences (PNAS), experts analyzed the effect of climate change on immigration from Mexico to the United States. Researchers chose to study Mexico because of the abundance of data on Mexican migration patterns, primarily based on factors such as labor demand shocks, demographic changes, U.S. immigration policy and the effects of trade agreements on agriculture. The paper concluded that as temperatures rise and crop yields shrink, many Mexicans will become climate refugees – individuals forced to find labor and establish livelihoods elsewhere.
The PNAS paper arrives while the federal government is challenging Arizona lawmakers, who have introduced a controversial state-level immigration policy. The report adds climate as a new element to the ongoing debate.
According to the study, every 10 percent reduction in crop yield will force an extra two percent of Mexicans between the ages of 15 and 65 to migrate to the United States. As a result, a total of 1.4 to 6.7 million Mexicans will immigrate north by 2080 (assuming global mean temperatures increase by 1°C to 3°C). The report follows recent findings from the U.S. National Research Council, which showed that just one degree Celsius in warming could decrease yields by five to 15 percent. In Mexico’s case, rising temperatures are expected to devastate key crops like corn.
Experts have studied environmental migration for some time, anticipating that increasing numbers of people will be displaced as regions become less productive. The World Bank has explained, “[D]uring periods of chronic environmental degradation…the most common responses by individuals and communities is to intensify labour migration patterns.” As the PNAS authors note,
“Changes in crop yields that result from climate change occur over broad geographical areas (unlike sea level rise, which directly affects only coastal regions), and are likely to lead to long-term population shifts (more so than episodic flooding, for instance, the effects of which tend to be transitory).”
The authors were fully cognizant of inherent uncertainties in their work, stating that the exact effect of carbon dioxide and temperature on crop yields is difficult to predict. They added that other factors besides decreased crop yields – such as climate-related changes in the amount of land that can be cultivated – are expected to affect migration patterns.
Of course factors beyond the natural and physical system will also play a role. “I wouldn’t take these numbers to the bank,” warned University of Guelph professor Barry Smit. He described certain “heroic assumptions” in the study, like the idea that economic and political situations will remain unchanged in coming years. Others have noted that declining fertility rates will reduce the pool of Mexicans forced to migrate.
Bradford Plumer at The New Republic summarized the complexities of studying the effects of climate change: “The social consequences of global warming are always the hardest things to predict. Immigration rates are never driven by physics alone, but depend on plenty of other factors… And it’s always difficult to tie specific social trends to climate change.”
Plumer’s message stresses an intrinsic difficulty in communicating and evaluating the impact of future climate changes. Climate change must be understood as a threat multiplier – a “catalyst for conflict”. While rising temperatures will lead to new problems and crises, they will also magnify and exacerbate existing ones. In a 2007 report titled National Security and the Threat of Climate Change, military leaders and experts asserted that climate change will intensify instability in the world’s most volatile regions. The report showed that rising temperatures will “result in multiple chronic conditions, occurring globally within the same time frame,” while traditional security threats involve “a single entity acting in specific ways and points in time.”
In the PNAS paper on immigration, authors echoed this sentiment:
“[U]nmanaged and unexpected climate-related migration could exacerbate a range of problems, including deterioration of ecosystems, slowing of regional economic development, disruption of human and political rights, and increased international conflicts and border fortification.”
Michael Oppenheimer, professor of geosciences and international affairs at Princeton University, who led the research team, added that climate change will not be “the single biggest factor driving immigration, but it could become among the largest.”
Although the study focused only on Mexican immigration, its implications are global. Climate change will dramatically reduce crop yields in regions such as Africa, India, Bangladesh, Latin America and Australia, and migration may become very likely.
While difficulty abounds in studying the social and political effects of climate change, the takeaway message is clear. Some of the most delicate problems we face today will only intensify as climate change introduces new, complex challenges. As evidenced by recent research, there is little doubt that pressure to migrate will increase as temperatures rise, affecting precipitation patterns and crop yields. While this indirect consequence of climate change can be managed with adaptation policies and programs, it could become just as grave as sea level rise or ocean acidification in the absence of social planning.