A few weeks ago several researchers from UC Berkley, including the impressive development economist Ted Miguel, published a study connecting a rise in temperature with the incidence and onset of civil war in Sub-Saharan Africa. You can find the paper here.
Last week the Times, the BBC, many other news outlets, dozens of blogs and climate change activists have been reporting the link and touting the paper’s claim that climate change will lead to a “54% increase in armed conflict incidence by 2030.”
I looked over the paper behind the result, and found that, while the study is interesting and well thought out, there are several reasons that the conclusions should be taken with a grain of salt.
1. The link between temperature and civil war is not rock solid.
Brad DeLong, quoting Richard Freeman, once mentioned three good rules of thumb for judging econometric results:
- It had better be there in the ordinary-least-squares regression.
- It had better still be there in the econometrically-sophisticated high-tech instrument procedures.
- It had better still be there for small technical tweaks to the econometrically-sophisticated procedures.
Of course, real analysis is more complex than this, but the rules are still a good starting point. We don’t actually see the basic OLS regression which is OK by today’s standards, but it would still be handy to see. For their main specifications, only one of the three models the authors present has statistical significance at the 5% level.
The choice of the 5% level, which roughly corresponds to the probability that the result is being generated by pure chance, as a measure of validity is (while a bit ad-hoc) the standard threshold from where you go “wow, these are interesting results” to “looks neat, shame that nothing’s significant.”
If you churn through the supporting tables (a separate document available here), you’ll find a mix of results, some of them significant at the 5% level, some at the 10% level (which is worse) and many not significant at all.
To make matters worse, the confidence intervals indicate that we’re 95% confident that the effect could be much larger (8%), much, much smaller (.01%), or anywhere in between. This may seem like nitpicking, but the true value of the coefficient (the effect of temperature changes on civil war) has huge implications for their resulting predictions. If it was closer to .01%, then we wouldn’t have quite so much to worry about. The authors use the whole distribution in their projection, but still use the median of their projected increase (which could be as low as 6.2%!).
2. There are a lot of if’s in the projections for 2030.
Projections like these are often made ceteris paribus (holding everything else constant). To their credit, the authors do use both optimistic and pessimistic projections on the growth of income and governance in these countries. However, they fails to account for the future in several ways – because their study fails to find any significant relationship between governance and/or income with civil war (a result I find very hard to accept), rising incomes and governance do very little to offset the probability of civil war in their model.
While we may not be able to make precise statements about exactly how much income it takes to avoid a civil war, I think it’s reasonable to assume that growth and good government do make civil war less likely. Furthermore, I’d expect that growth and good government might make also mitigate the effect of climate change on the probability of civil war (democracies are more likely to respond to weather-related disasters). There must be interaction effects going on, but they aren’t explored in the study.
3. If the projections are true, isn’t the answer still “civil war prevention” rather than “climate change” mitigation?
The paper and many of those citing it suggest that the answer to climate-fueled civil war is working at the country-level to mitigate the effects of rising temperatures. This might be so, but shouldn’t we also consider other ways of buffering countries against the incidence and duration of civil war? Most civil wars happen in an environment of extremely low governance, so how realistic is it to assume we can implement large-scale climate change mitigation in countries that are essentially failed states?
4. The long tail
I should note that I do believe that climate (obviously) plays a role in modern conflict – this isn’t the first study to suggest it. When your crops fail due to unusually warm temperatures, joining that marauding band chaps with AK-47s seem a little more reasonable. I think the study, which is open and honest about its approach, is certainly more reasonable than slapdash NGO reports which haphazardly total numbers from wildly different sources. It is a very interesting and worthwhile study, but I just think we should be hesitant to infer too much from it.
COP-15 is fast-approaching, and advocates are already adding “climate change will lead to a 50% increase in civil wars” to their list of arguments. I think climate change is very scary business, not because we know precisely what will happen, but because there are many known unknowns and unknown unknowns. Even if the expected damage turns out to be quite low, it is the long tail of the distribution that should be especially disquieting. This is what should prompt our efforts to offset the rise in global temperatures, not a barrage of unverifiable statistics.