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The article "Climate change and the Syrian civil war revisited" by Selby et al., 2017 (henceforth S2017) challenges research exploring the links between anthropogenic climate change, water scarcity and drought, impacts on agricultural production and economic stability, and the initial 2011 unrest in Syria. More broadly, the authors contest any causal link between climate and conflict. This is an important, evolving area of study and we encourage improved, expanded, and updated analysis of these connections. In their criticism, the authors of S2017 single out three papers (Werrell, Femia, & Sternberg, 2015; Gleick, 2014; and Kelley, Mohtadi, Cane, Seager, & Kushnir, 2015; here after K2015). Here we comment directly on our own work in K2015, though the others are equally unscathed by S2017's criticisms. We do so by refuting S2017's claims regarding the role of climate change, summarizing the sizeable evidence of the long-term drying trend in the region, and bolstering the link between the drought, migration and subsequent unrest by providing further supporting evidence. Our response contends overall that S2017 fail to make their case. K2015 (as well as Gleick, 2014; Werrell et al., 2015) claim climate as one of many contributing factors to the unrest. Nothing in S2017 refutes this, and none of their supportable arguments even offer reason for doubting this view. While K2015 can and did make a quantitative estimate of the impact of anthropogenic effects on the drought, we cannot quantify the impact of climate or any other factor, separately, on the conflict.

Significance: There is evidence that the 2007−2010 drought contributed to the conflict in Syria. It was the worst drought in the instrumental record, causing widespread crop failure and a mass migration of farming families to urban centers. Century-long observed trends in precipitation, temperature, and sea-level pressure, supported by climate model results, strongly suggest that anthropogenic forcing has increased the probability of severe and persistent droughts in this region, and made the occurrence of a 3-year drought as severe as that of 2007−2010 2 to 3 times more likely than by natural variability alone. We conclude that human influences on the climate system are implicated in the current Syrian conflict. Abstract: Before the Syrian uprising that began in 2011, the greater Fertile Crescent experienced the most severe drought in the instrumental record. For Syria, a country marked by poor governance and unsustainable agricultural and environmental policies, the drought had a catalytic effect, contributing to political unrest. We show that the recent decrease in Syrian precipitation is a combination of natural variability and a long-term drying trend, and the unusual severity of the observed drought is here shown to be highly unlikely without this trend. Precipitation changes in Syria are linked to rising mean sea-level pressure in the Eastern Mediterranean, which also shows a long-term trend. There has been also a long-term warming trend in the Eastern Mediterranean, adding to the drawdown of soil moisture. No natural cause is apparent for these trends, whereas the observed drying and warming are consistent with model studies of the response to increases in greenhouse gases. Furthermore, model studies show an increasingly drier and hotter future mean climate for the Eastern Mediterranean. Analyses of observations and model simulations indicate that a drought of the severity and duration of the recent Syrian drought, which is implicated in the current conflict, has become more than twice as likely as a consequence of human interference in the climate system.