The relationship between temperature and assault in New Zealand

A number of previous studies have reported a positive relationship between ambient temperature and the incidence of violent crimes such as assault. This has led some authors to suggest that anthropogenic climate change may result in an increase in violent crime rates. In this study, we report an investigation of the relationship between temperature and assault incidence in New Zealand. Both police data listing recorded assaults as well as data from the Ministry of Health listing hospitalisations due to assault were examined. Geographical, seasonal, and irregular daily variation in temperature were all positively related to the incidence of assault, although only the effect of irregular variation in temperature was robust to controls for plausible confounds. The estimated effect of irregular daily variation in temperature was approximately 1.5 % extra recorded assaults for each 1 °C increase in temperature. It remains difficult, however, to make accurate predictions about future assault rates in a warming world. For example, humans may react to sustained changes in climate in ways that differ markedly from their reaction to short-term variation in temperature. Climate change may also affect rates of violence via mechanisms other than those that currently drive the relationship between temperature and violence. Furthermore, assault rates may continue to change in response to factors unrelated to climate change, such as those responsible for the long-term historical decline in human violence.