Uncomfortable heat may interfere with policing and justice

If you feel irritable when it's too hot, you're not the only one. Decades of studies have found links between heat, aggression, and irritability, which, in turn, have been shown to increase criminal activity. Yet despite the relationship between heat and law breaking, little research has linked hot weather with decisions made by those who respond to criminal activity.

Writing in PNAS Nexus, a Stanford University team explores whether high temperatures may affect the decision-making of police officers, prosecutors, and judges. They find that hot weather seems to be linked to changes in decision-making of those in some criminal justice roles — with potential ramifications for those who are subject to it.

To understand the relationship between heat and law enforcement, the team used a dataset covering more than 10 million arrests in Texas between 2010 and 2017, including information on subsequent prosecutions and trials. Along with demographic details, the data also noted specific dates associated with arrests, charges, and rulings by judges, allowing events to be tracked against daily temperature data.

The information used by the team differed based on the role someone had within the criminal justice system. For police officers, data was gathered on how many arrests occurred compared to how many crimes were reported, in an attempt to capture whether police are more effortful and forceful on hot days. They also looked at the outcomes of cases for defendants arrested on hot days to understand whether or not officers are more likely to arrest people on subsequently non-prosecutable grounds during hot weather spells.

Next, the team focused on prosecutors — those who make decisions on whether there's enough evidence to pursue a case, or if charges should be changed or dropped. Again, two behaviours were measured: whether prosecutors are more or less likely to drop cases and whether additional charges are added on hot days.

Finally, judges. Here, the team explored whether or not cases were more or less likely to be dismissed on hotter days and recorded information about punishments issued by the court, including length of sentencing or probation, or the amount of fines issued.

Police made fewer arrests per reported crime on hot days, though arrests did increase overall when the weather was hotter. A larger proportion of these hot-day arrests ultimately resulted in dismissals compared to cooler days, with the difference between dismissal and conviction rates starting at temperatures above 26°C, and growing as temperatures increases.

This remained the case regardless of whether crimes were violent or non-violent; hot days had no specific impact on conviction or dismissal rates for assault, sexual assault or domestic violence. The authors suggest, therefore, that heat "may be having a deleterious effect on police decision-making." The exact mechanisms of this remain to be explored.

There was no evidence that prosecutors released defendants or dropped charges more or less on hot days than cooler days, however; there was some evidence that they were more likely to add more charges on hot days, but this result was only weakly significant. The team argues that this may be to do with the "diffuse decision-making process" in prosecutor offices; hot weather on one particular day, therefore, may be less likely to impact a decision.

Judges, however, consistently made less favourable decisions on hotter days. Unlike prosecutors, judges are making decisions alone, often on a single day, potentially increasing the likelihood of heat having an impact. Similarly, defendants received more severe punishments on hot days, with sentence length increasing by 6.5% on days with a temperature above 32°C. Fines also increased by around 4% when decisions were made on hotter days.

In a world where climate change and extreme weather events are increasingly relevant to our behaviour, and indeed how we function as wider societies, understanding the influence of heat on decision-making in justice contexts is vital. Future research efforts in this area may seek to better understand how to mitigate these effects, what other factors may be at play, and ensure that law enforcement — and decision-making more widely — is not influenced by uncomfortable temperatures.

Read the paper in full:

Behrer, A. P., & Bolotnyy, V. (2024). Heat and law enforcement. PNAS Nexus, 3(5). https://doi.org/10.1093/pnasnexus/pgad425