At Corcoran State Prison in the arid San Joaquin Valley of central California, the average outdoor summer heat index — or how hot it feels to the human body — often exceeds 100 degrees Fahrenheit.

An illustration of Corcoran State prison, showing the prison complex under a large sun during a hot summer day.

In 2024, every single summer day hit a heat index of at least 85 F.

An illustration of a housing unit at Corcoran State prison.

Built in 1988, the prison houses nearly 2,600 men, including Andre Peart, 57, who is serving a 25-years-to-life sentence in the minimum security section.

An illustration of Andre Peart sitting in his cell, looking out the window.

Corcoran State Prison has air-conditioning, but Peart’s experience with the heat and rising temperatures, exacerbated by climate change, illustrate systemic problems with how prisons are built and maintained.

An illustration of Andre Peart sitting in his cell, looking out the window.

“I know we’re here to do our time. We shouldn’t have to worry about having a heat stroke or a heart attack,” Peart said.

A close up illustration of Andre Peart. Sweat is dripping down his face.

Scorching cells

How heat threatens lives in America’s prisons

Prisons prioritize security over comfort. But concrete walls, steel doors, sealed windows, limited ventilation, lack of tree cover and outdated infrastructure converge to create dangerously hot conditions. Nearly 1.2 million people are housed in federal and state prisons across the nation.

Ufuoma Ovienmhada and Michael Krisch, researchers at the University of Arizona and the Brown Institute for Media Innovation at Columbia University, found in a study that 67.3% of 1,614 state and federal prisons had at least one day where the average summer outdoor temperature was over 85 F between 2020 and 2023. Some facilities in California, Arizona and Nevada experienced at least 65 days where temperatures exceeded 85 F.

There’s often little relief within the prison walls. Nearly half of state prisons across 29 states have partial or no air conditioning in housing units, according to an exclusive database created by Reuters using documents obtained through public records requests to all 50 states. The Bureau of Prisons, which oversees all 122 federal prisons, did not respond to Reuters’ request seeking information on how many facilities have air conditioning as of the time of publication.

Prison advocates say the hot conditions amount to unfair treatment and excessive punishment. Current and formerly incarcerated individuals told Reuters in a series of interviews that they dreaded summers. One person said the heat was so oppressive it felt like they were “breathing under water.” Legislative and policy efforts have stalled or failed to address the problem, even as prison populations and temperatures rise.

“A lot of people view incarcerated people as less than and not deserving of humane environmental conditions in the first place,” said Ovienmhada.

Prisons are often built in places that are relatively hot, secluded from areas where people don’t want them, said Bharat Venkat, director of the UCLA Heat Lab, an interdisciplinary research collective that studies thermal inequality. Unlike others exposed to extreme heat, incarcerated people don’t have access to the same modes of cooling – like fully functional air conditioning, unlimited access to water and ice or the ability to wear clothes made of breathable fabrics.

“It’s not about where it’s hotter, it’s really about where those impacts are felt most acutely,” said Venkat.

People of color are disproportionately represented among the U.S. prison population. At the end of 2022, Black people comprised 32% of the federal and state prison population, but only 14.4% of the total U.S. population. Experts attribute these disparities to a variety of factors, including systemic racism in policing practices and policies that disproportionately affect communities of color.

In a June 2025 report, the California Department of Corrections and Rehabilitation said that the cooling infrastructure in its prisons has degraded and become less effective, with climate change further exacerbating the problem. The report acknowledged that the buildings were built at a time when “the comfort level of the incarcerated population was not a consideration or priority.”

“Ensuring that CDCR facilities have adequate infrastructure is critical to the health and safety of the incarcerated population and staff,” said Mary Xjimenez, a spokesperson for CDCR, in an emailed statement. The CDCR said it has $246 million in projects underway to address cooling at five institutions and is working on a statewide plan to address the problem.

For Peart and other incarcerated individuals in California, there’s little respite yet.

“There is no getting away from it,” he said.

Concrete cells

Prisons create their own urban heat island effect, a phenomenon where built-up areas – like cities with little vegetation – have higher temperatures than their surrounding areas.

A 3D digital reconstruction of Peart’s prison cell, measuring roughly 70 square feet and shared with another inmate. The camera moves through the confined space, revealing the concrete walls, a small fan used to combat the oppressive heat, and a vent intended to circulate cool air into the room. The scene concludes by transitioning to a bird’s-eye view of the expansive Corcoran State Prison complex, placing Peart’s cell within the broader context of the facility.

This is a re-creation of Peart's cell. It's an approximately 70 square foot room that he shares with another person. He is surrounded on all sides by thick, concrete slabs that have a high thermal mass, meaning they absorb heat gradually during the day and release it slowly over time.

During the daytime, the exterior-facing wall of Peart’s cell absorbs solar radiation and can reach temperatures up to 15 F hotter than the cell’s air temperature, based on energy modeling done exclusively for Reuters by Engineering 350, a building engineering firm based in San Francisco.

Peart relies on a small fan for relief, purchased from the commissary for $25. A working CDCR incarcerated individual makes between 16 and 74 cents an hour. At the minimum hourly rate, it could take a month of work to buy a fan.

While fans help circulate air around a room, they do not decrease the overall temperature.

Peart's housing unit has a small vent above the toilet that brings in air from evaporative coolers but he says the air is not always cool.

When outdoor temperatures drop at night and individuals are locked in their cells, daytime heat stored in the walls radiates into the living spaces. Temperature logs from last summer at Corcoran show the average nighttime cell temperature was 80 F.

A 2023 report by Ella Baker Center, a non-profit advocacy group, found that 87% of surveyed incarcerated people in California state prisons noted the recreation yard they use most frequently has no shade covering. Studies have shown that shaded locations can drop temperatures by 20–45 F.

A 3D digital reconstruction of Peart’s prison cell, measuring roughly 70 square feet and shared with another inmate. The camera moves through the confined space, revealing the concrete walls, a small fan used to combat the oppressive heat, and a vent intended to circulate cool air into the room. The scene concludes by transitioning to a bird’s-eye view of the expansive Corcoran State Prison complex, placing Peart’s cell within the broader context of the facility.

Heat’s toll on prison life

Even when a prison has a cooling mechanism, its effectiveness can depend on the age and type of system, as well as maintenance.

“I would roll up my mattress just to lay on the cold steel of the bunk bed to get a little relief from some of those times when the AC would break down,” said Vanessa Rojas, who was formerly incarcerated at Federal Correctional Institution, a federal prison in Tallahassee, Florida.

The Bureau of Prisons, which oversees FCI Tallahassee, confirmed air conditioning outages in several locations of the prison during the time Rojas was incarcerated. A spokesperson said that inmates may be relocated if the air conditioning cannot be repaired quickly and it provides commercial fans for some relief.

At Arizona State Prison Complex in Yuma county, dust and dirt would often clog up the air vents, making it difficult for cool air to blow through, said John Fabricius, executive director of Praxis Initiative, a non-profit organization working on criminal justice reform. Fabricius was formerly incarcerated for 15 years across various Arizona prisons.

The Arizona Department of Corrections, Rehabilitation and Reentry told Reuters that since Ryan Thornell was appointed director in January 2023, by then-incoming Democratic Governor Katie Hobbs, the department has launched a program to address the problem of heat in prisons, and three of the five housing units at Yuma were now equipped with modern air conditioning.

In prisons where there is no air conditioning, indoor temperatures can be “at or even above the reported outdoor air temperature,” Ovienmhada said.

Studies have shown rising temperatures and multi-day heat waves, defined as days where the temperature is above the 90th percentile, contribute to an increase in mortality in prisons. Brown University epidemiologist Julianne Skarha estimated in 2023 that a 10 degree increase in summer temperature was associated with a 5.2% increase in prison deaths and suicides increased nearly 23% in the three days following an extreme heat day.

Certain medications – like the beta blockers Peart takes to treat atrial fibrillation, a heart condition that causes irregular heartbeats – make people more vulnerable to the adverse health effects of extreme temperatures by affecting how they regulate their body temperature.

“I get lightheaded and shaky and cannot work out on days when the temperature is high,” he said.

CDCR told Reuters that during extreme heat situations, facilities “may also provide additional access to cooling stations in air-conditioned areas, such as clinics and mental health spaces, as well as increased access to water stations, fans, portable cooling units and ice.”

Maria Goellner, senior director of state policy at Families Against Mandatory Minimums, a nonpartisan nonprofit that advocates for criminal justice reform, said the U.S. prison population is aging, with medical needs requiring medication that makes them more susceptible to high temperatures.

“Prison is a place where your conditions of confinement directly impact your medical state,” she said.

Between 1999 and 2016, the number of incarcerated adults aged 55 and over increased by 280%, compared to a 3% increase in those aged under 55, according to a 2018 report by Pew Charitable Trusts.

A need for cooling

The number of summer days each state prison surpassed a heat index of 85 F – often used as the upper limit to define comfort by some correctional facilities – is marked as a day that requires air conditioning.

A square histogram showing the number of days each state prison recorded a heat index above 85 degrees Fahrenheit. Each square represents a prison. While some require air conditioning for only one or two summer months, 266 prisons experienced heat above 85 degrees Fahrenheit for all 92 summer days, indicating a need for AC.

Heating, ventilation and air conditioning systems, commonly referred to as HVAC units, are typically designed using historical climate normals, which can create limitations on how much they can cool the interior. As global temperatures continue to rise due to climate change, the demand for cooling in buildings increases.

“Prisons were built at a very different time in our environment and even small increases means significantly higher frequency and severity of these dangerous heat events,” Krisch said.

Soaring numbers

Research shows the likelihood of disorders linked with prolonged exposure to heat begins when the heat index rises above 80 F.

Records of indoor temperatures indicate that levels can exceed 100 F, even in buildings that have HVAC systems. California State Prison-Los Angeles County, documented a day last July where temperatures soared to 104 F.

Monitoring the heat

One of the approximately 20,000 pages of temperature logs Reuters received and processed from the California Department of Corrections and Rehabilitation.

An image of an indoor temperature log from California Rehabilitation Center. Each indoor temperature log shows the institution and housing unit where the temperature is recorded. The temperature readings are taken eight times each day, every three hours starting at 3:00 a.m. and every time the temperature climbs above 90F (32C), the watch commander is to be notified.

Reuters received indoor temperature logs from California, Pennsylvania, Texas, Utah, and Washington through public records requests. While these logs provide a glimpse into conditions inside prisons and are often the only internal temperature records available to the public, experts say they should be scrutinized.

Corene Kendrick, deputy director of the ACLU National Prison Project, cited data from Arizona dating back to 2017 that she said was clearly inaccurate as it included temperatures in the future. She also said that incarcerated people told the ACLU that corrections officials would measure temperature “right in front of the vent where it was potentially the coolest.”

The Arizona spokesperson said that as part of its reforms, and “in contrast to previous eras,” its staff are now trained to properly record temperatures in housing units, “in the livable areas of cells, not just temperatures at vents.”

Internal temperature logs show hot conditions inside prisons

The average temperatures across all housing units for California prisons that were recorded every three hours by CDCR staff from June through August 2024.

A line chart showing internal temperatures recorded in California prisons from June through August 2024. Each line represents a different prison, with temperature readings taken every three hours by CDCR staff. The temperature ranges from the low 60s to the mid-90s Fahrenheit. Several annotations highlight health-related thresholds:

  • Between 68 degrees Fahrenheit and 76 degrees Fahrenheit: OSHA’s recommended indoor temperature range.
  • At 80 degrees Fahrenheit: Fatigue may occur with prolonged exposure or physical activity.
  • At 90 degrees Fahrenheit: Potential for heat stroke, heat cramps, or heat exhaustion.

Dangerous working conditions

Excessive heat also affects correctional employees. Regulations such as California's OSHA indoor heat guidelines require employers to either cool workplaces that get hotter than 87 F or take other precautions to minimize risk of heat-related illnesses. But there is an exception for correctional officers and other prison employees.

In the current U.S. federal legal landscape, the Federal Labor Standards Act does not apply to incarcerated people. Meanwhile, state employment laws are inconsistent in their classification of incarcerated workers. The 13th Amendment, which abolished slavery in 1865, made a carve-out for people convicted of a crime, allowing for slavery and involuntary servitude within prisons.

Fabricius said that the first job he had after he was incarcerated was on the “afternoon rock crew,” where he sometimes spent six hours working in extreme heat outdoors.

Research shows that violence in prisons increases as temperatures rise. A 2021 study found that daily violent interactions increased by 20% on days with unsafe heat index levels, and the probability of any violence increased 18%.

“Patience runs very thin, it’s a very dangerous environment,” Fabricius said.

No end in sight

Peart may spend the rest of his life in the California prison system, if he doesn’t get parole. He was convicted in 1997 of possession of a firearm, unlawful driving or taking of a vehicle and receiving stolen property. In 30 years, the average summer temperature at Corcoran State Prison is projected to be 3 F hotter due to climate change, according to research from Krisch.

Venkat supports closing down prisons as a long-term solution.

“If you close a couple of prisons, you save billions of dollars. And those billions can be used to make sure that you climate proof the remainder of carceral facilities,” he said.

The majority of prisons in the U.S. are owned and operated by individual states, resulting in a patchwork of policies across the country.

Ovienmhada said requiring modern air-conditioning systems in all prisons across the country sounds like an obvious solution but isn’t likely to happen, given political opposition and practical difficulties. Some facilities are so old that they don’t have the ductwork needed to install modern day air conditioning systems.

However, retrofitting air conditioning units into prisons or upgrading existing ones can be expensive. The CDCR estimates the cost of implementing statewide “effective air cooling mechanisms” at $6 billion. The California legislature approved a two-year program worth $37.6 million for CDCR to develop a future statewide plan to address indoor temperatures in its state prisons. In Arizona, the department said its upgrades to ASPC Yuma were subject to state financing.

“We would like to finish our work implementing HVAC, but we must work within the limited budget means allocated,” the spokesperson said.

As climate change drives temperatures higher, advocates say that outdated infrastructure, limited budgets and political resistance to reform leaves incarcerated individuals vulnerable.

“No one in America was sentenced to die of heatstroke in a prison,” said Goellner from Families Against Mandatory Minimums.

Corcoran State Prison in California, with a view of the prison yard and buildings. Corcoran State Prison in California, with a view of the prison yard and buildings.

Note

Summer temperatures are defined as June through August.

Reuters created a model of Peart's cell and Corcoran State Prison based on measurements provided by Peart, photo and video references of the prison and spatial data from OpenStreetMap.

Methodology

Learn more about Reuters' methodology for collecting public records and analyzing air conditioning and indoor temperature data here. Access the data on GitHub.

Contributing reporters

Gloria Dickie, Soumya Karwa, Prinz Magtulis

Additional development

Sudev Kiyada

Edited by

Kat Stafford, Julia Wolfe, Claudia Parsons