Was the drought really responsible? Assessing statistical relationships between climate extremes and cultural transitions

It is commonplace to assert causal relationships between episodes of extreme climate with dramatic cultural shifts. We explore the problem of statistically assessing the correspondence between episodes of extreme climate (such as droughts) and cultural events (such as depopulation) they are purported to explain. In order to do this: 1) We describe a method that permits the objective identification of climate extremes in a way that is independent of their supposed causal outcomes; 2) We discuss how we identify and date cultural transitions of interest; 3) We explore a variety of decision rules for determining whether or not there is a match between a given extreme climate interval and the interval during which a transition began; and 4) We propose an intuitive Monte Carlo approach to statistically assess the observed correspondence between the climate extremes and the cultural transitions. Our application does not indicate statistical support for a linkage between intervals of extreme climate and major transitions in any of the seven cultural traditions in the Southwest US that we examined.