Extreme weather events and military conflict over seven centuries in ancient Korea.

We explore the causal connection between weather and war by constructing and analyzing a dataset featuring extreme weather events and military conflicts involving a set of stable political entities that existed side by side over several centuries, namely, the three ancient kingdoms of the Korean Peninsula between 18 Before the Common Era and 660 Common Era. Conflicts are classified as desperate if a state experiencing the shock invades a neighbor and opportunistic if a state experiencing the shock is invaded by a neighbor. We find that weather-induced conflict was significant, but largely opportunistic rather than desperate. That is, states experiencing an adverse shock were more likely to be invaded, but not more likely to initiate attack. We also provide evidence that the channel through which weather shocks gave rise to opportunistic invasions was food insecurity, which weakened the power of states to repel attack. Since climate change is projected to give rise to an increased frequency of extreme weather events, these historical findings have contemporary relevance.

Air pollution, respiratory illness and behavioral adaptation: Evidence from South Korea.

Air pollution is closely associated with the development of respiratory illness. Behavioral adaptations of people to air pollution may influence its impact, yet this has not been investigated in the literature. Our hypothesis is that people experience and learn the underlying air quality to decide their adaptation, and they have a stronger incentive to behaviorally adapt to the air quality as it deteriorates. We tested our hypothesis on a sample of approximately 25,700 individuals from South Korea from 2002 to 2013 that contained information on daily doctor's visits due to respiratory disease. We matched individuals to the mean of the past seven-day concentration of the particulate matter of size between 2.5 and 10 micrometers (PM10) in their county of residence. We examined whether people living in counties with greater air pollution suffer less from respiratory disease when the concentration increases. For the analysis, we separated counties into quintiles based on their mean seven-day PM10, and regressed the binary indicator of a daily doctor's visit with a resulting diagnosis of respiratory disease on the seven-day PM10 concentration of the county of residence interacted with the quintile dummies. The key findings are that a 1-standard-deviation increase in the seven-day PM10 concentration in the two lowest quintiles is associated with an increase of 0.054 percentage points in the likelihood of a doctor's visit with a resulting diagnosis of respiratory disease, which is about 40% larger than the effect in higher quintiles, and the size of 1-standard-deviation gradually increases from 0.037 percentage points in the third quintile to 0.040 percentage points in the fifth quintile. The smaller increase in the likelihood of respiratory disease in more polluted locations can be explained by the behavioral adaptation to the environment, but the effectiveness of the adaptation seems limited among the highly polluted locations.