Therefore, it is not necessary to explicitly control for many other social and economic factors that also affect emigration.
Statistical identification comes from the considerable climate variability within Mexican states that occurred in the two 5-y periods under study: 1995 to 20 to 2005.
Furthermore, the possible impacts of climate change on the agriculture sector have been estimated worldwide and are relatively well understood (23–25).
Specifically, we study Mexico for the decade of 1995 to 2005, during which time a substantial increase in out-migration to the United States occurred.
For that reason, this study uses an approach that isolates the climate effect—which may have only been secondary—from other drivers of historical migration to provide a basis for the estimation of future international immigration flows.
Several aspects of climate change may drive changes in migration (20).
Studies have examined numerous factors underlying the so called “great Mexican emigration” (26–31), including negative labor demand shocks, labor supply shocks resulting from demographic changes, US immigration policy changes, migrant networks, and importation of cheap corn and other agricultural products following the North American Free Trade Agreement (NAFTA) (32).
We chose Mexico for our study because it is one of the biggest migrant-source countries, because there exists state-level data on emigration, and because it has undergone diverse degrees of climate variability across regions.
Despite qualitative assertions and some local case studies (7, 8, 15, 16) (, part 1), climate-driven migration has not received sufficient attention in the immigration literature.
Existing studies of immigration typically emphasize the roles of geographic proximity, relative economic opportunities for potential migrants, social and cultural networks, and political stability as causative factors.
Among all potential “climate refugees” or “environmental migrants,” those crossing international borders are likely to be of particular concern for both developing (in many cases, migrant-sending) and developed (i.e., migrant-receiving) countries.
Although migration is a normal part of the development process (10, 11), and can be an important risk management strategy for households (12, 13), unmanaged 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 (14).