Will climate change increase or decrease suicide rates? The differing effects of geographical, seasonal, and irregular variation in temperature on suicide incidence

Abstract

The effect of environmental temperature on suicide risk is an important issue given the increase in global temperatures expected over the following century. Previous research has produced conflicting findings: Studies concerned with temporal variation in temperature and suicide have tended to find a positive relationship, while those concerned with geographical variation in temperature and suicide have tended to find a negative relationship. In this study, we aimed firstly to estimate the relationship between suicide incidence and three components of variation in temperature: Irregular, seasonal, and geographical. Secondly, we aimed to critically examine what this information can (and cannot) tell us about the likely effects of anthropogenic climate change on suicide rates. Suicide data from New Zealand for the period 1988 to 2007 were collated according to date of death and district and compared with temperature data from the same period. Using generalized linear mixed models, we found that irregular variation in temperature was positively related to suicide incidence, with about 1.8 % more suicides for every 1 °C increase in temperature. On the other hand, seasonal variation in temperature had virtually no linear relationship with suicide incidence, and when controlling for demographic differences, geographical variation in temperature was negatively related to suicide incidence. We conclude that differences in both the sign and the direction of the effects of different forms of variation in temperature mean that it is very difficult to predict how climate change will affect risk of suicide.