Linkages among climate change, crop yields and Mexico–US cross-border migration

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

Climate Change, Agriculture and Migration: A Survey

“…In the second stage, the predicted crop yields are used to explain outmigration from Mexican States towards the US. The authors argue that this method allows one to identify the relationship between crop yields and migration without explicitly controlling for other confounding factors [96]. This statement is correct if weather variables are a true source of exogenous variation in crop yields or, to put it differently, if they represent valid instruments.…”

“…First, the authors of this paper have shown that, due to the neglect of time fixed effects in [96], many common factors potentially confounding the true effect, such as the NAFTA, the Peso crisis, etc., are not controlled for in the proposed specification. Second, and more importantly, by replicating the results obtained in [96], they have shown that, when time effects are controlled for, the statistical evidence of a causal relationship between weather-driven yield shocks and emigration disappears, which casts doubts on the fact that a truly causal effect may have been picked up.…”

“…The first contribution, to be found in [96], focuses on the emigration from Mexico to the US in the 1995-2000 and 2000-2005 periods. The authors identify the causal effect exploiting a 2SLS approach and using weather variables as instruments for crop yields in a panel data context with state fixed effects.…”

“…In principle, the approach used by [96] is econometrically valid for estimating the causal effect of crop yields on outmigration. However, some important qualifications have been made by [97].…”

“…Macro-studies can be distinguished between those based on gravity-like (bilateral) migration equations, as in [10,80], and those exploiting panel data econometrics, as in [54,96].…”