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Tuesday, July 27, 2010

Climate Change South of the Border

Feng et al. recently released this paper in PNAS on climate change, crop yields in Mexico, and migration. Although quite timely, the study unfortunately stops short of discussing the larger equity implications of the work. The idea that increased migration pressure could result as a consequence of climate change could add a new dimension to the immigration debate. What responsibilities do developed nations have to environmental migrants given historical responsibilities for greenhouse gas emissions and climate change?


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 ofemigration 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 additional2%of the population
toemigrate.Wethen 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.

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