Climate change and conflict in Africa 

 A paper  just published in PNAS  finds that armed conflict in Africa in recent decades has been more likely in hotter years, and projects that warming in the next twenty years will result in roughly 54% more conflicts and almost 400,000 more battle deaths. This is an important paper and it probably will attract significant attention from the media and policymakers. I think it's a good paper too -- seems fairly solid in the empirics, nice presentation, and admirably forthright about the limitations of the study. I'll explain a bit about what the paper does and what questions it leaves.  

 To establish the historical connection between temperature and conflict in Africa, the authors conduct a panel regression with country-level fixed effects, meaning that they are examining whether conflict is more likely in a given country in unusually hot years. Their main model also includes country time trends, so it seems that they are not merely capturing the fact that the 1990s had more conflict than the 1980s due to the end of the Cold War and also happened to be hotter due to the overall warming trend. In a supplement that I was not able to access, they show that  the correlation between temperature and conflict is robust to a number of other specifications. So the pattern of more conflict in especially-hot years seems fairly robust. (Arguments to the contrary very welcome.) They then link this model up to a climate model to produce predictions of conflict in the next twenty years, under the assumption that the relationship between temperature and conflict will remain the same in the future. 

 Given that hot years saw more conflict in the 1980s and 1990s, should we expect a hotter Africa to have more conflict in the future? To some extent this depends on why hot years saw more conflict in the past. The authors note that hotter temps can depress agricultural productivity by evaporating more water and speeding up crop development, and they view this as the most likely channel by which hot temperatures lead to more conflict. They also note that hot weather has been shown in other settings to increase violent crime and make people less productive, and they admit that they can't rule out these channels in favor of the agricultural productivity story. If it's a matter of agricultural productivity, then adjusting farming techniques or improving social safety nets could avoid some of the projected conflict; if the main issue is that especially hot weather makes people rash and violent then there may not be much to do other than reverse the global process (and possibly provide air conditioning to potential insurgents). Overall the "policy implication" from the paper seems to be that changes that should happen anyway seem more urgent.  

 To be more confident about the paper's projection I'd like to see more detail about the mechanism -- even just anecdotal evidence. I'd also like to hear about whether politics in Africa seems to have changed in any way that would make a model of weather and conflict from the 1980s and 1990s less applicable now and in the future.