Interpersonal violence associated with hot weather
Authors: Rahini Mahendran, Rongbin Xu, Shanshan Li, Yuming Guo
Journal: The Lancet Planetary Health (2021)

The anthropogenic climate change has numerous adverse health effects, such as heat-related morbidity and mortality, respiratory diseases from wildfire smoke, rise of prevailing and novel vector-borne and water-borne infectious diseases following a drought or flood, and death or injury due to storms or flooding.1Watts N Amann M Arnell N et al.The 2020 report of The Lancet Countdown on health and climate change: responding to converging crises.Lancet. 2021; 397: 129-170Summary Full Text Full Text PDF PubMed Scopus (316) Google Scholar, 2Haines A Ebi K The imperative for climate action to protect health.N Engl J Med. 2019; 38: 263-273Crossref Scopus (277) Google Scholar However, the potential effect of high temperature on increased interpersonal violence, in the context of climate change, has received much less attention. A growing body of research suggests that rising temperature increases some violent crimes, such as intentional homicides,3Xu R Xiong X Abramson MJ Li S Guo Y Ambient temperature and intentional homicide: a multi-city case-crossover study in the US.Environ Int. 2020; 143105992Crossref PubMed Scopus (10) Google Scholar sex offences,4Xu R Xiong X Abramson MJ Li S Guo Y Association between ambient temperature and sex offense: a case-crossover study in seven large US cities, 2007–2017.Sustain Cities Soc. 2021; 69102828Crossref Scopus (1) Google Scholar and assaults.5Kubo R Ueda K Seposo X Honda A Takona H Association between ambient temperature and intentional injuries: a case-crossover analysis using ambient records in Japan.Sci Total Environ. 2021; 774145511Crossref PubMed Scopus (4) Google Scholar In a retrospective study in seven US cities, every 5°C rise in daily mean temperature between 2007 and 2017 was associated with a 4·5% increase in sex offences in the following 0–8 days.4Xu R Xiong X Abramson MJ Li S Guo Y Association between ambient temperature and sex offense: a case-crossover study in seven large US cities, 2007–2017.Sustain Cities Soc. 2021; 69102828Crossref Scopus (1) Google Scholar A nationwide analysis in Japan between 2012 and 2015 found that ambulance transports due to assault increased linearly with the rise in daily temperatures.5Kubo R Ueda K Seposo X Honda A Takona H Association between ambient temperature and intentional injuries: a case-crossover analysis using ambient records in Japan.Sci Total Environ. 2021; 774145511Crossref PubMed Scopus (4) Google Scholar Violent incidents also showed a seasonal distribution by which most crimes happened in the summer or hot seasons than in winter.3Xu R Xiong X Abramson MJ Li S Guo Y Ambient temperature and intentional homicide: a multi-city case-crossover study in the US.Environ Int. 2020; 143105992Crossref PubMed Scopus (10) Google Scholar, 6Hipp JR Bauer DJ Curran PJ Bollen KA Crimes of opportunity or crimes of emotion? Testing two explanations of seasonal change in crime.Soc Forces. 2004; 82: 1333-1372Crossref Scopus (117) Google Scholar Hence, interpersonal violence in hot weather is likely to continue and increase in the future with increasing temperature due to climate change. In a 2014 paper, Matthew Ranson found that there could be an additional 22 000 murders, 1·2 million aggravated assaults, and 2·3 million simple assaults because of climate change in the USA by the end of this century as compared with 2010.7Ranson M Crime, weather and climate change.J Environ Econ Manag. 2014; 67: 274-302Crossref Scopus (154) Google Scholar There are two main theories that can help explain a positive association between ambient temperature and violent crime. The first theory, known as biological theory or temperature-aggression theory, explains that hot weather induces interpersonal violence by increasing discomfort, frustration, impulsivity, and aggression.6Hipp JR Bauer DJ Curran PJ Bollen KA Crimes of opportunity or crimes of emotion? Testing two explanations of seasonal change in crime.Soc Forces. 2004; 82: 1333-1372Crossref Scopus (117) Google Scholar However, this theory does not explain the increases in violent crime in areas where the temperature has risen from cold to warm,3Xu R Xiong X Abramson MJ Li S Guo Y Ambient temperature and intentional homicide: a multi-city case-crossover study in the US.Environ Int. 2020; 143105992Crossref PubMed Scopus (10) Google Scholar, 4Xu R Xiong X Abramson MJ Li S Guo Y Association between ambient temperature and sex offense: a case-crossover study in seven large US cities, 2007–2017.Sustain Cities Soc. 2021; 69102828Crossref Scopus (1) Google Scholar, 5Kubo R Ueda K Seposo X Honda A Takona H Association between ambient temperature and intentional injuries: a case-crossover analysis using ambient records in Japan.Sci Total Environ. 2021; 774145511Crossref PubMed Scopus (4) Google Scholar as temperature rise in this range is unlikely to cause uncomfortableness. Such settings require the second theory, known as routine activity theory, which suggests that change in ambient temperature can alter people's routine activities (eg, outdoor events and social contacts) and increase interpersonal conflicts or create suitable crime environments.8Cohn EG Weather and Crime.Br J Criminol. 1990; 30: 51-64Crossref Scopus (159) Google Scholar It is also important to consider the role of interrelated demographic, socioeconomic, cognitive, personality, and biological factors that affect the way a person reacts. Studies that have investigated temperature-violence associations to date are only preliminary. There could be other contributing factors to various violent acts that have been not captured and might modify temperature associations. For example, a strong temperature–homicide association was found in US cities with high population-density, young age, low proportion of men and White people, and high income inequality. This finding suggests that the temperature–violence associations could be modified by local socioeconomic and demographic factors. Thus, an association observed in one place is unlikely to apply directly to another setting. Further studies, particularly studies in multiple communities and countries, are warranted to explore potential modifying factors, such as age, sex, ethnicity, socioeconomic status, cultural beliefs, law system, and gun control policy. Qualitative studies, such as interviews with police, hospital staff, offenders, and survivors, would also provide insights into the potential mechanisms. The term interpersonal violence, covers a wide range of behaviours, but studies investigating climate change and violence typically focused on the extreme forms of violent crime, such as assault, sexual offences, and homicide. Interpersonal violence in the forms of sexual and psychological harassments, particularly partner violence, has been neglected. Therefore, more research is needed on other forms of interpersonal violence occuring both outdoors and indoors in the context of a changing climate. The measures that could help to prevent violent crimes related to temperature rise also remain uncertain. One potential suggestion is the use of heat-warning systems to alert law enforcement agencies of the high temperature and potential increase in violence, but this would need to be evaluated in future studies. Public safety awareness programmes, help lines, gun control policies, and controls on alcohol use could be used as levers to reduce violent crimes.9Klostermann KC Fals-Stewart W Intimate partner violence and alcohol use: Exploring the role of drinking in partner violence and its implications for intervention.Aggress Violent Behav. 2006; 11: 587-597Crossref Scopus (166) Google Scholar, 10WHOViolence prevention: the evidence. WHO press, Malta2010Google Scholar Spatial differences in violent incidents are likely to require locally targeted preventive measures, such as police patrolling in the streets during hot days, camera surveillance, and assigning additional security patrols to at-risk areas. The best way to integrate these general crime prevention measures with temperature data and forecasts warrants further investigations. In summary, there is increasing evidence that is suggestive of a relationship between temperature and violence at the population level. Without effective mitigation measures, there could therefore be an increase in interpersonal violence as the temperature continues to increase. Further studies in multiple communities and countries are warranted to investigate the relationships further, evaluate modifying factors, underlying mechanisms, and possible risk mitigation strategies. We declare no competing interests.