Global trade and the resilience of food supply to extreme weather exposure

Climate change is increasing the risk of extreme weather events, potentially threatening crop yields and global food security. A key benefit of international trade is risk sharing, because global aggregate production is more stable than that of individual countries which may be adversely affected by extremes. However, countries vary in the degree to which they source commodities from trading partners, potentially exposing supply chains to shocks induced by extreme weather. Global patterns of extreme weather exposure in crop supply chains are poorly understood. Here we test the hypothesis that diverse sourcing of crops from multiple trading partners is associated with reduced exposure to extreme weather, using a detailed trade matrix and the Emergency Event Database (EM-DAT). EM-DAT drought and extreme heat events are significant predictors of negative yield shocks for many crops. We find that countries with high source diversity have low to moderate extreme exposure as predicted by theory, but that there is wide variation in the degree of exposure in countries reliant on domestic crop production. Self-sufficient countries therefore have among the highest and lowest levels of extreme exposure, while diverse importers tend to have intermediate levels of exposure. Global aggregate production and export volatility are stable or declining for most crops, suggesting that source diversification and increasing international trade could promote resilience to both climatic and non-climatic supply shocks. However, governmental impositions of export restrictions in response to perceived food security threats, including extreme weather, can trigger price rises and shortages in importers. Hence the impacts of extreme events can be exacerbated by policies designed to protect domestic food security.