Intense heat raises the risk of violence in American prisons

LAST YEAR was a violent one in Mississippi’s prisons. There were 853 inmate-on-inmate assaults, a rise of 29% compared with 2019. Officials argue that much of the violence is gang-related—factions fighting over territory or contraband such as cellphones. Activists point out that punitive policies, shortages of staff and derelict facilities play a role, too. Another, and probably underestimated, factor may be the weather. Mississippi summers usually see average temperatures rise above 80℉ (26.7℃), a threshold at which the likelihood of violence in prisons increases.

That is the finding of a working paper by Anita Mukherjee of the University of Wisconsin-Madison and Nicholas Sanders of Cornell University. The authors matched county-level weather variations across Mississippi with violent incidents reported in the state’s 36 prisons and jails between 2004 and 2010. Using these data, they built a statistical model that controlled for the time of year that the violence took place, the type of institution and other factors. They calculated that on days with average temperatures of 80℉ or higher the chances of violence increased by 20%. The hot weather leads to an average of 44 additional incidents of severe violence—those that result in serious injury or death—each year.

The influence of heat on violent behaviour has been documented before. For example, research has shown that on hot days pitchers in Major League Baseball games are more likely to hit batters (through aggression rather than accident, it is thought). Other studies have found that homicides and violent crime in cities such as Chicago and Los Angeles peak on the hottest days.

But measuring the influence of heat on violent behaviour is not an exact science. The studies have to account for variables that may skew results. A baseball player may find relief from the heat between innings in the team’s climate-controlled clubhouse. Warm weather also encourages people to spend time outdoors, increasing social interactions that could lead to violence. Other variables, such as income and reporting bias, must also be considered.

Prisons offer a controlled setting to study the interplay of heat and violence, according to Ms Mukherjee and Mr Sanders. Mississippi is one of eight American states that do not provide air conditioning throughout “most” of their prison system, according to the Prison Policy Initiative, an advocacy group. Inmates often cannot mitigate heat by retiring to an air-conditioned room or taking a cold shower. Cold water for drinking may not be available on hot days—sometimes ice is intentionally withheld—and dodgy plumbing adds to its scarcity. Prisons built of metal and glass, which conduct and retain the summer heat, raise the temperature further.

Advocates of prison reform argue that housing inmates in facilities without air conditioning violates the Eighth Amendment, which prohibits “cruel and unusual punishments”; in some cases the courts have sided with them. Many inmates suffer from health problems and illnesses, such as hypertension and diabetes, that extreme heat can exacerbate. In Texas the deaths of more than 13 inmates over the past decade due to heat exposure prompted lawsuits, some still pending, against the state.

Worsening heat waves and droughts may augur more violent summers for American prisons. According to the Department of Justice, prison homicides in 2018 (the latest year for which data are available) hit the highest rate since 2001. About 30% of the estimated 2m incarcerated people in America are imprisoned in one of the eight states without universal air conditioning. Most of these states lie in America’s southern heat belt, where summer temperatures easily cross the 80℉ threshold. Ms Mukherjee and Mr Sanders estimate that unmitigated heat could trigger 4,000 additional violent incidents across America’s prison system. These prison fights can lead to additional convictions and extended sentences, as they are tried as separate incidents.

There are some efforts to improve conditions in prisons. Activists and inmates have won lawsuits in several states, where courts ruled that not providing climate-controlled housing for inmates vulnerable to extreme weather violated their rights under the Eighth Amendment. In May the Texas house of representatives voted to require the state to purchase air-conditioning units so that prison temperatures could be maintained between 65℉ and 85℉. The bill capped the cost of doing so at $300m over seven years, but the state’s criminal-justice department claimed it would cost three times that amount. The bill has not had a reading in the senate. For the 80,000 inmates without air conditioning in Texas, it is likely to be another sweltering summer.

Correction (July 27th 2021): an earlier version of this article misstated the units in the right-hand chart.