Abstract: Any act of battlefield violence results from a combination of organizational strategy and a combatant's personal motives. To measure the relative contribution of each, our research design leverages the predictable effect of ambient temperature on human aggression. Using fine-grained data collected by US forces during the Afghanistan and Iraq conflicts, we test whether temperature and violence are linked for attacks that can be initiated by individual combatants, but not for those requiring organizational coordination. To distinguish alternative explanations involving temperature effects on target movements, we examine situations where targets are stationary. We find that when individual combatants have discretion over the initiation of violence, ambient temperature does shape battlefield outcomes. There is no such effect when organizational coordination is necessary. We also find that ambient temperature affects combat-age males’ endorsement of insurgent violence in a survey taken during the conflict in Iraq. Our findings caution against attributing strategic causes to violence and encourage research into how strategic and individual-level motivations interact in conflict.

A number of studies have demonstrated an empirical relationship between higher ambient temperatures and substate violence, which have been extrapolated to make predictions about the security implications of climate change. This literature rests on the untested assumption that the mechanism behind the temperature-conflict link is that disruption of agricultural production provokes local violence. Using a subnational-level dataset, this paper demonstrates that the relationship: (1) obtains globally, (2) exists at the substate level--provinces that experience positive temperature deviations see increased conflict; and (3) occurs even in regions without significant agricultural production. Diminished local farm output resulting from elevated temperatures is unlikely to account for the entire increase in substate violence. The findings encourage future research to identify additional mechanisms, including the possibility that a substantial portion of the variation is brought about by the well-documented direct effects of temperature on individuals' propensity for violence or through macroeconomic mechanisms such as food price shocks.