``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.''
``Discussion
To conclude, we have examined the link between climate-driven productivity changes in the agricultural sector and out-migration with Mexico used as an example. Our results are conservative in at least two respects. First, projected changes in crop yields are considerably larger than those observed in our data. If crop yield affects emigration in a nonlinear fashion, our linear specification would likely underestimate the full impact of climate on crop yields in the future. Second, as we focus on only crop yields, our estimate provides a lower bound for the overall impact of climate change on emigration through agriculture, which could also be affected by changes in the total acreage of land cultivated. Even so, the estimated elasticity of emigration with respect to crop yield changes is statistically significant and large in a practical sense. This suggests that crop yield–induced migration will be a significant issue in many areas of the world that are expected to experience a substantial reduction in yields as a result of climate change, including much of Africa, India, Bangladesh, Latin America, and Australia, among others. Because climate change may induce out-migration through channels not examined in this study, the overall effect may be larger, particularly if atmospheric greenhouse gas concentration levels continue to increase sharply and countries fail to implement aggressive adaptation measures.
Given these projections, certain migrant-receiving countries, including the United States, are expected to face increased migration streams as a result of existing transnational networks with migrant-sending countries that are particularly vulnerable to climate change. However, some aspects of the Mexico/United States emigration situation are also unique, so extrapolation of our quantitative findings to the global level would be inappropriate. Nevertheless, application of our methods to other regions and other climate-related drivers of immigration, and to internal migration, would provide insights into potential future immigration and migration “hot spots,” as well as into the overall magnitude of the looming changes. Additional insights concerning the response of migration sensitivities to trends in climate variables (i.e., whether the semielasticity would decrease or increase in a different climate) may also be gained from study of regions with data sets extending over a longer period. Future research could also use different methods (e.g., ethnography) to complement our statistical approach to deepen our understanding of people’s motives to migrate when faced with climate change.''
``Discussion
To conclude, we have examined the link between climate-driven productivity changes in the agricultural sector and out-migration with Mexico used as an example. Our results are conservative in at least two respects. First, projected changes in crop yields are considerably larger than those observed in our data. If crop yield affects emigration in a nonlinear fashion, our linear specification would likely underestimate the full impact of climate on crop yields in the future. Second, as we focus on only crop yields, our estimate provides a lower bound for the overall impact of climate change on emigration through agriculture, which could also be affected by changes in the total acreage of land cultivated. Even so, the estimated elasticity of emigration with respect to crop yield changes is statistically significant and large in a practical sense. This suggests that crop yield–induced migration will be a significant issue in many areas of the world that are expected to experience a substantial reduction in yields as a result of climate change, including much of Africa, India, Bangladesh, Latin America, and Australia, among others. Because climate change may induce out-migration through channels not examined in this study, the overall effect may be larger, particularly if atmospheric greenhouse gas concentration levels continue to increase sharply and countries fail to implement aggressive adaptation measures.
Given these projections, certain migrant-receiving countries, including the United States, are expected to face increased migration streams as a result of existing transnational networks with migrant-sending countries that are particularly vulnerable to climate change. However, some aspects of the Mexico/United States emigration situation are also unique, so extrapolation of our quantitative findings to the global level would be inappropriate. Nevertheless, application of our methods to other regions and other climate-related drivers of immigration, and to internal migration, would provide insights into potential future immigration and migration “hot spots,” as well as into the overall magnitude of the looming changes. Additional insights concerning the response of migration sensitivities to trends in climate variables (i.e., whether the semielasticity would decrease or increase in a different climate) may also be gained from study of regions with data sets extending over a longer period. Future research could also use different methods (e.g., ethnography) to complement our statistical approach to deepen our understanding of people’s motives to migrate when faced with climate change.''
Taken from PNAS
Two Princeton professors and one Chinese scientist foresee more Mexicans heading North. The document was released ten days ago. I just saw it today.
I believe them; therefore this week's Arizona Law has to be defeated by the Obama Administration, or by the year 2080, Arizonan children, some of them brown, will be asking their parents why were they so wrongheaded?
The boat is sinking people, let us face this rationally.
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