Linkages among climate change, crop yields and Mexico–US cross-border migration
- aWoodrow Wilson School of Public and International Affairs, Princeton University, Princeton, NJ 08544;
- bSchool of Economics, Shanghai University of Finance and Economics, Shanghai 200433, China;
- Departments of cEconomics and
- eGeosciences, Princeton University, Princeton, NJ 08544; and
- dUS Department of Treasury, Washington, DC 20220
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Edited* by Stephen H. Schneider, Stanford University, Stanford, CA, and approved June 24, 2010 (received for review March 3, 2010)

Abstract
Climate change is expected to cause mass human migration, including immigration across international borders. This study quantitatively examines the linkages among variations in climate, agricultural yields, and people's migration responses by using an instrumental variables approach. Our method allows us to identify the relationship between crop yields and migration without explicitly controlling for all other confounding factors. Using state-level data from Mexico, we find a significant effect of climate-driven changes in crop yields on the rate of emigration to the United States. The estimated semielasticity of emigration with respect to crop yields is approximately −0.2, i.e., a 10% reduction in crop yields would lead an additional 2% of the population to emigrate. We then use the estimated semielasticity to explore the potential magnitude of future emigration. Depending on the warming scenarios used and adaptation levels assumed, with other factors held constant, by approximately the year 2080, climate change is estimated to induce 1.4 to 6.7 million adult Mexicans (or 2% to 10% of the current population aged 15–65 y) to emigrate as a result of declines in agricultural productivity alone. 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.
- human migration
- global warming
- environmental migrants
- agricultural productivity
- instrumental variables approach
Footnotes
- 1To whom correspondence should be addressed. E-mail: omichael{at}princeton.edu.
Author contributions: S.F., A.K., and M.O. designed research; S.F., A.K., and M.O. performed research; S.F. analyzed data; and S.F., A.K., and M.O. wrote the paper.
↵*This Direct Submission article had a prearranged editor.
The authors declare no conflict of interest.
This article contains supporting information online at www.pnas.org/lookup/suppl/doi:10.1073/pnas.1002632107/-/DCSupplemental.
Freely available online through the PNAS open access option.
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