It has been proposed that changes in global climate have been responsible for episodes of widespread violence and even the collapse of civilizations1,2. Yet previous studies have not shown that violence can be attributed to the global climate, only that random weather events might be correlated with conflict in some cases3,4,5,6,7. Here we directly associate planetary-scale climate changes with global patterns of civil conflict by examining the dominant interannual mode of the modern climate8,9,10, the El Niño/Southern Oscillation (ENSO). Historians have argued that ENSO may have driven global patterns of civil conflict in the distant past11,12,13, a hypothesis that we extend to the modern era and test quantitatively. Using data from 1950 to 2004, we show that the probability of new civil conflicts arising throughout the tropics doubles during El Niño years relative to La Niña years. This result, which indicates that ENSO may have had a role in 21% of all civil conflicts since 1950, is the first demonstration that the stability of modern societies relates strongly to the global climate.
S.M.H. was supported by Environmental Protection Agency Science to Achieve Results grant FP-916932 and a postdoctoral fellowship in Applied Econometrics at the National Bureau of Economic Research; K.C.M. was supported by the Paul and Daisy Soros Fellowship for New Americans. We thank W. B. MacLeod, B. Salanié, A. Sobel, J. Sachs, W. Schlenker, E. Miguel, D. Almond, S. Barrett, G. Heal, M. Neidell, J. Mutter, N. Keohane, A. Cassella, J. Currie, W. Kopczuk, C. Pop-Eleches, R. Fisman, S. Naidu, M. Humphreys, D. Lobell, M. Roberts, M. Greenstone, M. Biasutti, G. Wagner, G. McCord, J. Anttila-Hughes, R. Fishman, A. Tompsett, A. Neal, B. R. Chen and seminar participants at Columbia, Massachusetts Institute of Technology, Stanford, University of California Santa Barbara, Environmental Defense Fund, the National Bureau of Economic Research Summer Institute and the American Geophysical Union Fall Meeting for suggestions. We also thank H. Buhaug and M. Burke for sharing replication materials.
This file contains STATA datasets and STATA code to replicate the results of this study. Results can be automatically replicated using STATA software version 11.1 or later.