[T]he persecution and expelling of Jewish people by pre-modern European states is linked to agrarian variations. Based on historical weather data, evidence suggests that during the 15th and 16th centuries, colder temperatures made it significantly more likely that a Jewish community would be expelled. … [A] Jewish individual from the 15th or 16th century, who lived to 50 years old, faced roughly an 18% chance of being expelled during their lifetime. This risk was almost twice as great during a cold year. (source)
Apparently, persecution of Jewish groups follows from the economic hardship that in turn follows from colder temperatures during the growing seasons (that is, April to September). Agrarian economies were more vulnerable to weather shocks, and these shocks produced negative economic outcomes which then led to the scapegoating of minorities. Cities with poorer quality soil also saw an increased chance in the occurrence of expulsions of Jewish groups.
Interesting, but I doubt it has much relevance for the problems of today.
More posts in this series are here.