Background
The authors write that "despite many claims by high-ranking policymakers and some scientists that climate change breeds violent conflict, the existing empirical literature has so far not been able to identify a systematic, causal relationship of this kind" - see, for example, Bruckner and Ciccone (2007, 2010), Buhaug (2010), Ciccone (2011), Theisen et al. (2011/12) and Bergholt and Lujala (2012) - which failure, in their words, "may either reflect de facto absence of such a relationship, or it may be the consequence of theoretical and methodological limitations of existing work."

What was done
In a study designed to explore these two possibilities, Koubi et al. "examine the causal pathway linking climatic conditions to economic growth and to armed conflict," as well as the degree to which this pathway is contingent upon the political systems of the potential conflict participants, using data "from all countries of the world in the period 1980-2004."

What was learned
The four Swiss researchers say their results suggest that "climate variability, measured as deviations in temperature and precipitation from their past, long-run levels (a 30-year moving average), does not affect violent intrastate conflict through economic growth," which finding, as they continue, "is important because the causal pathway leading from climate variability via (deteriorating) economic growth to conflict is a key part of most theoretical models of the climate-conflict nexus." They note, however, that they find "some, albeit weak, support for the hypothesis that non-democratic [i.e., "autocratic"] countries are more likely to experience civil conflict when economic conditions deteriorate," but they add that even this extremely weak connection "is fragile with regard to model specification."

What it means
In light of Koubi et al.'s significant negative findings, as well as the similar findings of many of the researchers they cite, it would appear that we should be leery of the claims of "high-ranking policymakers" that "climate change breeds violent conflict," for such has yet to be conclusively demonstrated to be the usual result.

References
Bergholt, D. and Lujala, P. 2012. Climate-related natural disasters, economic growth, and armed civil conflict. Journal of Peace Research 49: 147-162.

Bruckner, M. and Ciccone, A. 2010. International commodity prices, growth, and civil war in sub-Saharan Africa. Economic Journal 120: 519-534.

Bruckner, M. and Ciccone, A. 2007. Growth, democracy, and civil war. Social Science Research Network (http://ssrn.com/abstract=1028221).

Buhaug, H. 2010. Climate not to blame for African civil wars. Proceedings of the National Academy of Sciences USA 106: 20,670-20,674.

Ciccone, A. 2011. Economic shocks and civil conflict: A comment. American Economic Review: Applied Economics 3: 215-227.

Theisen, O.M., Holtermann, H. and Buhaug, H. 2011/12. Climate wars? Assessing the claim that drought breeds conflict. International Security 36: 79-106.