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Johannesburg - South Africa has one of the highest homicide rates on record at an estimated 36 per 100000 individuals, roughly six times the global average.

The country is also experiencing climate warming at a faster rate than the global average. And this, say the authors of a new study, “heightens the importance of understanding potential relationships between temperature and adverse health and social outcomes such as homicide”.

The team from the US, SA and Italy aimed to investigate the short-term association between daily ambient temperature and homicide in SA, using daily temperature data and a national mortality data-set from Statistics SA that included all recorded deaths from 1997 to 2013.

“Our findings indicate evidence of a positive association between short-term increases in ambient temperature and the odds of death by homicide,” they write in Short-Term Association Between Ambient Temperature and Homicide in South Africa: A Case-Crossover Study.

There were 246229 cases across all districts in SA over the full study period, including both definite (68356) and probable (177873) homicides, “which equates to a mean of ~40 per day. Maximum daily temperature ranged from 0.5°C to 47.8°C.”

The authors found a 1°C increase in same-day maximum temperature was associated with a 1.5% increase in definite homicides and a 1.2% increase in total (definite + probable) homicides.

The authors reported that a hotter day makes a homicide more likely on that day, as well as on the next day.

“This temperature-health relationship may be of particular concern in the context of climate change,” they write in the study, which was published in the journal Environmental Health, on December 16.

“The ability to include meteorological variables as a predictor of criminal activity and violent behaviour could prove valuable in resource allocation for crime-prevention efforts.”

Traditionally criminology research has investigated socio-demographic predictors of crime, such as sex, race, age and socio-economic status.

“However, evidence suggests that short-term fluctuations in crime often vary more than long-term trends, which socio-demographic factors cannot explain.”

This has redirected researchers to explore how environmental factors, such as meteorological variables, influence criminal behaviour.

“Several theories have been proposed to explain possible mechanisms underlying these relationships, including that temperature may influence behaviour, for example by changing the probability of convergence between a likely offender and suitable target, or by altering patterns of alcohol consumption.

“Biological theories suggest weather changes or extremes may act as a stressor that facilitates aggression.”

Previous studies indicate that “violent crime” as a broad category (often including murder, assault, burglary, domestic violence and/or rape) may be positively associated with ambient temperature “but evidence on the relationship between temperature and homicide specifically is more limited”, they write.

“Overall, our findings align with the existing literature investigating temperature and broad categories of violent crime.

“For example, a recent study in the US investigated 301 counties across 34 states, and reported a significant and approximately linear positive association between violent crime and daily temperature.”

The authors cite two local studies conducted in Tshwane on weather/climate and violent crime.

“One reported a 50% increase in violent crime on hot days compared to very cold days, while the other found that less affluent neighbourhoods had higher rates of assault in the summer than more affluent neighbourhoods but similar rates during the winter.”

A recent paper (see sidebar) on the links between heat and homicide reviewed 16 studies, noting that nine reported a significant positive association whereas the others reported positive but non-significant associations.

“The paper also raised concerns about the relationship between climate change and violence in South Africa specifically.”

For the present study, daily temperature data was drawn from the National Oceanographic and Atmospheric Association of the US and the Agricultural Research Council.

Reported deaths include information on the date of death, cause of death according to the 10th revision of the International Classification of Disease and the location of death at the level of district municipality, of which there are 52 in SA.

“As violent deaths are known to be under/misreported in South Africa, we define two categories of cases. The first includes cases where the immediate or underlying cause of death was recorded as a homicide. We refer to this category as ‘definite’ homicides.

“The second includes violent deaths recorded as accidental or of undetermined intent that we consider likely to be homicides based on prior literature exploring this issue we refer to this group as ‘probable’ homicides.

“The two groups together comprise the ‘total’ homicides.”

The temperature-homicide relationship may be of particular concern in the context of climate change, especially in the absence of short-term adaptation, the authors write.

“Identification of areas and populations at risk for higher levels of violence due to short-term changes in temperature, combined with a more thorough understanding of the pathways by which these changes influence behaviour, could prove beneficial to policy measures such as those employed during heatwaves.

“This ability to include meteorological variables as a predictor of criminal activity and violent behaviour could prove valuable in resource allocation for violence prevention efforts and preparedness for first responders and healthcare providers.”

The authors are Abigail Gates, Mitchel Klein and Noah Scovronick of the Department of Environmental Health at Rollins School of Public Health at Emory University in Atlanta in the US; Fiorella Acquaotta of the Department of Earth Sciences at the University of Turin, Italy and Rebecca Garland of the Smart Places Cluster at the CSIR.

Understanding connections between heat and violence crucial as SA warms 

Evidence indicates interpersonal violence may increase in uncomfortably hot temperatures. This is according to a guest editorial in the South African Medical Journal last July.

“Countries like South Africa, which already have high levels of violence and a rapidly warming climate, may be particularly vulnerable to this under-appreciated consequence of climate change,” states the paper, Violence in Hot Weather: Will Climate Change Exacerbate Rates of Violence in South Africa?

The research was led by Associate Professor Matthew Chersich from the Wits Reproductive Health and HIV Institute. “There may be a considerable increase in the number of cases of homicide and other forms of violence per year should the mean temperature rise by 1°C, signalling the potential for an even greater burden of violence, centred on already vulnerable groups.” 

Other consequences of climate change, such as extreme weather events, “eco-migration” and conflict over food and water, “could in themselves raise levels of collective violence and transnational conflict”, the paper finds.

Triggers of violence, such as heat, are set against the backdrop of complex social processes, poor governance and historical circumstances that influence violence, states the paper. 

“Clearly, more detailed assessments are required of the linkages between heat and violence in South Africa, and interactions between these and other factors. Such analyses may have important practical implications for violence-prevention strategies in the country, and indeed globally.” 

While violence in South Africa has been attributed to the unique historical, social and economic characteristics of the country, the potential contribution of physical environmental factors such as heat has largely been ignored. “Understanding connections between heat and violence is increasingly important as we witness the warming of our planet, and anticipate more intense and longer-lasting heatwaves in the coming decades.”  

Meteorological conditions, especially temperature, can profoundly influence a person’s physiology and behaviour, states the paper. “Heat exposure can affect levels of comfort, emotional stability and sense of wellbeing. 

Being in an uncomfortably hot environment foments irritability and aggressive thoughts, and reduces positive emotions such as joy and happiness.” Men appear to be particularly sensitive to the effects of heat on aggression. “Hot weather also alters behaviours, for example, resulting in people tending to congregate outdoors, with increased opportunities for contact crimes and violence. 

“Additionally, alcohol use, a potent trigger for violence, can increase during hot weather, while dehydration, more common on hot days, is associated with mood disturbance, confusion and anger. “It’s therefore plausible that together these physiological and behavioural pathways may increase the likelihood of violence, particularly violence committed with the intention of harming other persons rather than violence where the aim is primarily to gain assets, such as robberies.”

The degree to which heat impacts on violence varies across settings and is contingent on factors such as gun control, gender inequalities, substance abuse and socio-economic vulnerability. 

The paper notes how “surprisingly few studies” have examined the impact of temperature on rates of violence in South Africa, despite a wealth of available data. Chersich and his team of co-authors summarised the established evidence on the association between temperature and murders, and of the 16 targeted studies in the field, nine reported an increase in homicides with a rise in temperature. 

“While the remaining studies did not detect a significant association, they were all in the direction of a positive effect. Effect size ranged widely, from small effects in some studies in the US to an estimated 17% increase in homicides per year in Africa were the temperature to increase by 1°C. 

“Based on the findings of these studies and using a conservative estimate of a 4% to 5% increase in homicides per degree rise in temperature, we estimate that the current number of homicides per year in South Africa (20 336) will increase by between 800 and 1 000 should the temperature in the country rise by 1°C.” Additional modelling work using empirical data is needed to refine this estimate.

The paper says a more detailed understanding of heat-violence pathways could “help identify practical ways of ameliorating the ‘felt effects of heat’ and thus violence in these ‘hotspots’.” Air conditioning and fans could be used in “cooling zones”, operating in selected areas in specific workplaces, schools and prisons at high risk, the research recommends.

Chersich’s co-authors are Fiona Scorgie of the Wits Reproductive Health and HIV Institute; Callum Patrick Swift of the Tallaght University Hospital in Dublin; Ian Edelstein of the Human Sciences Research Council; and Greg Breetzke, Francois Schutte and Caradee Wright of the Department of Geography, Geoinformatics and Meteorology at the University of Pretoria. 

The Saturday Star