A new study by Robert Warren Anderson, Noel Johnson and Mark Koyama suggests that, historically, economic shocks were more strongly associated with outbreaks of violence directed against Jews than scholars had previously thought. The authors collected data for 1,366 anti-Semitic events involving forced emigration or murderous pogroms in 936 European cities between 1100 and 1800. This was then compared with historical temperature data from a variety of sources, including tree rings, Arctic ice cores and contemporary descriptions of the weather.
Cold spells hit medieval agriculture hard: a one-degree Celsius fall in temperatures reduced the growing season by up to four weeks. Lower yields caused widespread economic pain: up to 57% of people relied on farming for work in medieval England, for instance. The authors find that a fall in average temperatures of only a third of a degree increased the probability of a pogrom or expulsion by 50% over the next five years. They argue that violence against Jews was not simply caused by religiously-motivated anti-Semitism: “The Jews were convenient scapegoats for social and economic ills.”
The authors find that economic shocks had greater effects where soils were less suited to farming or where governments were weaker, and so less able to stop violence.Via Marginal Revolution citing the Economist. The closed access paper is here.
While the data above is specific to anti-semitic pogroms in Europe, there are fairly strong indications in the archaeological record (for example, from Southern Colorado during prehistoric droughts there), that this is a universal and global phenomena.