Wednesday, May 8, 2013

Is peace needed in the climate/conflict debate?

Yes, argues Andy Solow in a comment in Nature today.  He bemoans the "fierce battle that has broken out within the research community" over whether there is a link between climate and conflict, highlighting the protracted argument we've been having with Halvard Buhaug and colleagues over whether there is a link between temperature and conflict in Africa (see here, here, and here).  Solow's main point seems to be that these sorts of "reduced form" analyses of climate and conflict reveal little about the true underlying processes that drive conflict, and thus that people running these models ("quants") need to engage with folks that are studying individual conflicts in depth ("quals") to make the analyses meaningful.

Overall his comments are quite reasonable, and if I can speak for my co-authors I think we are sympathetic to many of his arguments.  I have a few main points of disagreement, however.  First, I would not characterize the disagreements between Halvard (and colleagues) and us as a disagreement between "quants" and "quals".  We would certainly put ourselves in the former category and I'm guessing Halvard would too.  The disagreements between us have really been about how to do the quantitative analysis correctly, something over which we continue to disagree and will continue to disagree as long as folks are estimating panel models without fixed effects, or estimating models that include outcome variables as covariates.  But contrary to what Solow suggests, we definitely have been engaging with Halvard and his colleagues.  For instance, at Halvard's generous invitation I participated in a couple sessions on climate and conflict at last month's annual meeting of the International Studies Association, sessions organized by Halvard and colleagues. 

More importantly, though, I think Solow misperceives what estimating reduced form models is all about in this setting, and does not allow that the very reason a "quants" might want to engage with a "quals" is because a reduced form effect has been established.  A typical quant approach would be to start with an initial hunch that conflict and (say) temperature might be related, put together some data, and estimate a regression of conflict on temperature.  If there is a relationship in this "reduced form", then this would motivate more careful study of the underlying cases and mechanism - i.e. an engagement with the quals.  On the other hand, if there is no relationship in the reduced form, there is arguably no reason to take a "deeper look behind the statistics", as Solow puts it.  This is because the reduced form effect is going to encompass all possible ways in which climate will affect conflict (even if it doesn't illuminate them), and a null result in the reduced form would tell you that there is no mechanism linking the two phenomena.  

(Some initial hint at the underlying mechanism can certainly motivate how the reduced form is estimated, and this is something people are already attentive to.  For instance, suppose you think that shortfalls in income are what link climate variables to conflict events; in a setting where income is earned in agriculture, then focusing on climate during growing season months might make sense.  This approach for example is pursued in a nice paper by Harari and La Ferrara, in which they show that drought during the growing season matters a lot more for conflict than drought in the non-growing season.)  

The argument with Halvard and colleagues is about whether there is a reduced form effect.  Because my colleagues and I think that the reduced form relationship between temperature and conflict in Africa has been pretty well established by different research groups working at multiple scales (e.g. here, here, here, here, and here), we are in full agreement with Solow that a closer look at mechanism is now warranted, and that we need to learn a lot from quals about what might be going on.  But if you do not believe this reduced form, then it doesn't make sense to engage with quals on how climate might affect conflict.  

But a reduced form relationship is also much more than just a reason to talk to qualitative folks.  For the sake of argument, let's imagine that no manner of further engagement with quals is ever able to fully isolate the mechanism linking climate to conflict - perhaps there are just too many factors that are both affected by climate and that are potential contributors to conflict.  Does this mean that we learn nothing from the reduced form, or that it should be ignored by policy-makers?  

Probably not, for two reasons.  First, the reduced form effect of climate on conflict, when properly estimated, is estimating the causal effect of climatic fluctuations (typically inter-annual) on conflict outcomes.  This is because year-to-year variation in climate is pretty random and unlikely correlated with other unobserved variables that also affect conflict.  We know climate has "caused" conflict, we just don't know why.  

Second, even if we don't yet understand the mechanism linking the two variables, the fact that warmer temperatures and conflict are linked would appear useful to policymakers interested in whether we should take action to mitigate future climate change.  Clearly, as Solow points out, past responses to year-to-year variation and future response to long-run changes in means are not the same thing.  But given that adaptation to long-run temperature changes appears very slow at best, that sensitivity to extreme heat does not appear to be diminishing, and that past relationships are all we really have to go on, then assuming these relationships might carry into the future does not seem like a crazy place to start.  Moreover, important decisions are often made solely on "reduced form" evidence.  For example, I don't need to know how snake venom kills me to figure that, if I find myself in a room full of poisonous snakes, it might make sense to either invest in snake-proof boots or see if I can find a door.  The "adaptation" strategy here - buying boots - does involve knowing a little something about the mechanism: i.e. snake --> bite --> die;  the "mitigation" strategy - leaving the room - does not.  As a less prosaic example, aspirin was discovered before 1900 and was prescribed for decades before the mechanism underlying its efficacy was understood in the 1960s. Similarly, quinine has been used as a malaria drug since the 1600s although we still do not understand why it works.  So failing to understand a mechanism does not typically keep us from taking meaningful action when we've decided a reduced form effect is real.

Nevertheless, I hope (with Solow) that we can stop arguing about a few of the primary reduced forms in question -- e.g. the link between temperature and conflict in Africa -- and do more to understand what's going on and what to do about it.  Doing so will help inform adaptation investments in particular, and Solow is right that detailed case-study knowledge from the "quals" will be critical in building this understanding.  But moving in this direction involves establishing that there is a reduced form relationship between temperature and conflict, and it is for this reason we are arguing with Halvard and co.  

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