The European Union (EU) has seen an unprecedented wave of immigration in 2015 as part of a larger surge in migration across the Mediterranean Sea that began in 2014. Many of the migrants flee war-torn countries such as Syria, Afghanistan, or Iraq, and there is an active debate as to whether a change in climatic conditions has contributed to, and will amplify, such migration flows. The Pentagon calls climate change a “threat multiplier.” We take a step back and investigate the role of weather shocks in global distress-driven migration to the EU in 2000–2014, i.e., preceding the recent crisis. Asylum applications to the EU from the 103 source countries in our sample totaled 1.5 million in 2015, that is, more than 4 times the average in our sample period.
We find a highly significant between logged asylum applications and average temperature over the maize growing area and season for the 103 source countries in our sample. If we average the weather on the basis of population in a grid cell, the temperature variables are no longer significant, which suggests that weather shocks over the agricultural area are the crucial channel. Applications are lowest for average temperatures around 20°C and increase if the weather is too cold or too hot.
We link anomalies in log applications to weather anomalies once common annual shocks are absorbed (e.g., the global financial crisis in 2008). Our specification examines whether hotter-than-normal temperatures will increase or decrease asylum applications from a given source country. Because our dependent variable is in logs, we estimate relative impacts, which is preferable as the number of applications differs greatly among source countries in absolute terms. We allow the effect to vary by the average weather variable: Hotter-than-usual temperatures can reduce asylum applications for cold countries and increase them for hot countries.
There are several likely mechanisms behind the sensitivity of fluctuations in asylum applications to temperature anomalies. First, there is a strong nonlinear relationship between agricultural yields and temperature. Moderate temperatures (i.e., in the lower 20°C range) over the growing season are ideal, with both hot and cold temperatures reducing yields. Second, gross domestic product (GDP) growth rates have been found to be very sensitive to temperature, even on the nonagricultural components of the GDP and even in industrialized countries. For both yields and GDP, being too hot is worse than being too cold. An improvement in agricultural output or GDP will help producers and workers (if they are paid their marginal product, which increases) in those regions, reduce the incentive to join criminal activity, and lead to less conflict. Third, the same sign in the relationship with weather is found for aggressive behavior, which increases with temperatures that have been shown to reduce output. This relationship holds consistently across several spatial and temporal scales. The first two mechanisms are a priori conducive to increased distress-driven migration in the event that weather deviates from the moderate optimum, and all three predict that increases in very warm locations are likely to be associated with higher asylum applications.