Ambient temperature and the occurrence of collective violence: the "long, hot summer" revisited.

Archival data pertaining to 102 instances of serious collective violence were examined in order to study the relationship between ambient temperature and the occurrence of such events. Results indicated that the frequency of collective violence and ambient temperature were curvilinearly related. Specifically, ambient temperature was directly associated with the frequency of collective violence through the mid-80s (degrees Fahrenheit). Beyond this point, however, further increments in temperature were associated with a decreasing incidence of such events. Additional findings indicated that ambient temperature increased significantly during the 7 days preceding the outbreak of collective violence, remained stable during its occurrence, but then decreased significantly in the 3 days following its termination. Possible implications of these findings, as well as their relationship to the results of previous laboratory studies, are discussed.