Attributing excess conflict risk in Syria to anthropogenic climate change

Some analyses suggest that drought in Syria during 2007-10 may have contributed to the 2011 onset of its civil war and that anthropogenic climate change had a detectable impact on the severity of that drought. Yet these qualitative statements alone do not allow us to estimate {how much} anthropogenic climate change amplified the risk of civil war in Syria. Climate policy is increasingly relying on global-scale cost-benefit analyses to inform major decisions, and any excess conflict risk imposed on future populations should be considered in this accounting because of its substantial human and economic impact. In order for this excess conflict risk to be accounted for, it must be quantified and its uncertainty characterized. Here we build on multiple recent findings in the literature to construct a best estimate for the excess conflict risk borne by Syria in 2010 that was attributable to anthropogenic climate change. We estimate that the baseline risk of conflict in Syria, which was likely already high, was amplified roughly 3.6% (90% confidence interval: 1.1-7.3%) due to the anthropogenic component of the drought. The effect of climate change was thus discernible but unlikely responsible for the bulk of Syrian conflict risk. Nevertheless, the magnitude of similar excess risk around the globe is expected to grow as climate change progresses, and its human cost could be large because most populations will face positive excess risk. Our approach to quantifying this risk is applicable to these other settings.