A recent Nature article on climate’s impact on conflict has generated controversy in the environmental security community for its bold conclusions about links between the global El Niño/La Niña cycle and the probability of intrastate conflict.

Authors Solomon Hsiang, Kyle Meng, and Mark Cane of Columbia and Princeton Universities called their study, the results of which were published in late August, “the first demonstration that the stability of modern societies relates strongly to the global climate.” However, their methodology and conclusions have faced some criticism and renewed a spirited debate over the links between the environment and conflict.

Though efforts have been made in the past to link conflict and climate, the authors write that their study stands out for several reasons:

• The methodology is statistical (using data from 1950 to 2004), not anecdotal;
• In place of local changes, such as rainfall patterns and extreme weather events, they use a truly global climate change (El Niño/Southern Oscillation) as their benchmark;
• By aggregating countries into collections rather than counting them individually, their “probability of conflict” measurement mitigates potential distortions due to the increase in the number of countries during the time period; and
• The correlation found is not driven exclusively by Africa.

The results, according to Hsiang et al., indicate that the El Niño/Southern Oscillation (ENSO) “may have had a role in 21 percent of all civil conflicts since 1950” and “the probability of new civil conflicts arising throughout the tropics doubles during El Niño years relative to La Niña years.”

The authors suggest that their findings could help us prepare for some conflicts and their associated humanitarian crises, since strong ENSO events are predictable up to two years in advance. But their fairly tame policy recommendations did not sway some critics.

“Horrifically Flawed”: A Strong Critique

In Foreign Policy, Charles Kenny points out some of the study’s limitations: The findings do not apply to anthropogenic climate change or interstate conflict; do not explain the specific mechanisms that link conflict and climate; and should be considered an additive – not primary – explanation for any conflict. Given these caveats, the title of the study is perhaps a bit misleading, but the authors do recognize all these limitations in the text.

Edward Carr, a professor in South Carolina’s Department of Geography and visiting AAAS fellow at USAID, had what may be the strongest critical response. In a post on his blog Open the Echo Chamber, he called the study “horrifically flawed, to the point that I cannot see how its conclusions actually tell us anything about the relationship between El Niño and conflict, let alone climate and conflict.”

Hsiang – the lead author of the study – responded, point by point, to this critique, and Carr replied in kind, giving readers an interesting glimpse at some of today’s central academic arguments around the connections between climate and conflict. The full exchange is worth a read, but here are some of the highlights.

In response to Carr’s criticism that their regression “is populated with massively over-aggregated data such that any causal signal is completely lost in the noise,” Hsiang writes:

It is true that our data is the most aggregated social data that we have ever seen analyzed (it summarizes the conditions for half the world’s population) and often aggregation makes signal detection difficult. However, this only makes the fact that we can extract a signal from the noise that much more remarkable. Despite everything else in the world that’s going on, we can observe a signal from ENSO loud and clear. And not only do we observe a single correlation, but we observe four patterns all of which point towards the idea that ENSO affects conflict.

And in answering Carr’s criticism of the study’s apparent assumption that livelihoods are “somehow optimized for one state or the other” and therefore “the populations affected by these changes were somehow perpetually surprised by the state change,” Hsiang writes:

This is incorrectly conflating two issues. (1) whether individuals are surprised about the *timing* of an El Niño event (2) whether individuals are surprised about what an El Niño climate looks like for them [and how they can optimize their life under those conditions].

We actually would expect that individuals on the ground are familiar with what El Niño conditions look like and what kinds of choices will optimize their livelihoods under some given ENSO conditions (because each state occurs frequently). However, we do not expect that most individuals know a year in advance whether the next year with be an El Niño year or not. For our research design to be valid, all we need is for individuals on the ground to have difficulty anticipating *when* El Niño events occur. The fact that they have observed an El Niño before does not threaten the scientific validity of the research design.

Open Questions

In short, Carr’s concerns seem condensable to two main issues. First, though the authors provide disclaimers in the text, the popular take-away will be that the climate causes conflict – a false environmental determinism that is bolstered by snappy headlines and opportunistic editorializing. Marc Levy wrote a critique of this oversimplification phenomenon after publication of a similarly controversial article by Halvard Buhaug last year, and it does not look like an issue that is likely to go away. Second, Carr remains unconvinced that there are strong links between conflict and climate and wants the authors to better explain them. This too is an open question for the field.

The authors found a statistical correlation between natural, predictable shifts in global climate – the ENSO effect – and incidences of civil conflict, but they are not sure why the correlation exists, offering instead a general theory:

Precipitation, temperature, sunlight, humidity and ecological extremes can adversely influence both agrarian and non-agrarian economics. In addition, ENSO variations affect natural disasters, such as tropical cyclones, and trigger disease outbreaks. All of these have adverse economic effects, such as loss of income or increasing food prices, and it is thought that economic shocks can generate civil conflict through a variety of pathways. Furthermore, altered environmental conditions stress the human psyche, sometimes leading to aggressive behavior. We hypothesize that El Niño can simultaneously lead to any of these adverse economic and psychological effects, increasing the likelihood of conflict.

Articulating the specific roles that the environment plays in local conflict is critical, and Carr is right to point this out, particularly if we want to plan for the effects of climate change. Levy in his post last year wrote:

To say something credible about climate change and conflict, we need to be able to articulate future pathways of economics and politics, because we know these will have a major impact on conflict in addition to climate change. Since we currently lack this ability, we must build it.

I think it’s fair to say that these pathways remain unclear and much work remains to be done to identify the specific links between conflict and climate. Though they don’t provide the answer, Hsiang, Meng, and Cane’s work should help in that effort.