Study evaluates the impact of summer heat in US prison environments

As summer temperatures rise, so does our vulnerability to heat-related illness and even death. Typically, people can take steps to reduce their heat exposure by opening a window, cranking up the air conditioning, or simply grabbing a glass of water. But for people who are incarcerated, the freedom to take such steps is often not an option. Prison populations are therefore particularly vulnerable to heat exposure due to the conditions of confinement.

A new study by MIT researchers looks at summer heat exposure in prisons across the United States and identifies features within prison facilities that may further contribute to a population’s vulnerability to summer heat.

The study authors used high-spatial-resolution air temperature data to determine the daily average outdoor temperature for each of 1,614 prisons in the U.S., for every summer between 1990 and 2023. They found that the prisons exposed to the most extreme heat are in the Southwest of the U.S., while prisons with the greatest changes in summer heat, compared to historical records, are in the Pacific Northwest, the Northeast, and parts of the Midwest.

These findings aren’t entirely unique to prisons, as any non-prison facility or community in the same geographic locations would be exposed to similar outdoor temperatures. But the team also looked at features specific to prison facilities that could further increase an incarcerated person’s vulnerability to heat exposure.

They identified nine such facility-level characteristics, such as severely restricted movement, poor staffing, and inadequate mental health care. People living and working in prisons with any of these characteristics may be at increased risk from summer heat.

The team also looked at the demographics of 1,260 prisons in their study and found that the prisons with higher average heat exposure also had higher percentages of non-white and Hispanic populations. The study, to appear today in the magazine GeoHealthprovides policymakers and community leaders with ways to assess and respond to heat risk to prison populations, which they anticipate will only increase with climate change.

“This isn’t a problem because of climate change. It’s going to be a bigger problem because of climate change,” says lead study author Ufuoma Ovienmhada SM ’20, Ph.D. ’24, a graduate of the MIT Media Lab who recently received her doctorate from MIT’s Department of Aeronautics and Astronautics (AeroAstro). “A lot of these prisons aren’t built to be comfortable or humane in the first place. Climate change is just exacerbating the fact that prisons aren’t designed to allow prisoners to moderate their own exposure to environmental risk factors like extreme heat.”

Co-authors of the study include Danielle Wood, an associate professor of media arts and sciences at MIT, and Brent Minchew, an associate professor of geophysics in the Department of Earth, Atmospheric and Planetary Sciences at MIT, as well as Ahmed Diongue ’24, Mia Hines-Shanks of Grinnell College, and Michael Krisch of Columbia University.

Environmental Crossroads

The new study is an extension of work done at the Media Lab, where Wood leads the Space Enabled research group. The group aims to advance social and environmental justice issues through the use of satellite data and other space technologies.

The group’s motivation to research heat exposure in prisons came in 2020 when Ovienmhada, as co-president of MIT’s Black Graduate Student Union, participated in community organizing activities following the killing of George Floyd by Minneapolis police.

“We started doing more organizing on campus around policing and reimagining public safety. Through that lens, I started learning about policing and prisons as interconnected systems, and I started seeing this intersection of prisons and environmental hazards,” says Ovienmhada, who is leading an effort to map the different environmental hazards facing prisons, jails and detention centers. “In terms of environmental hazards, some of the most acute impacts on inmates are extreme heat.”

She, Wood and their colleagues set out to use Earth observation data to characterize the vulnerability of US prison populations, or their risk of negative heat effects.

The team first examined a database maintained by the U.S. Department of Homeland Security, which lists the locations and boundaries of detention centers across the U.S. From the database of more than 6,000 prisons, jails, and detention centers, the researchers selected 1,614 prison-specific facilities, which together incarcerate nearly 1.4 million people and employ about 337,000 staff members.

Next, they looked at Daymet, a detailed weather and climate database that tracks daily temperatures across the United States at a resolution of 1 kilometer. For each of the 1,614 prison sites, they mapped the daily outdoor temperature for every summer between 1990 and 2023, noting that most current state and federal correctional facilities in the U.S. were built before 1990.

The team also obtained U.S. Census data on each facility’s demographic and facility characteristics, such as prison labor activities and confinement conditions. One limitation of the study that the researchers acknowledge is a lack of information on a prison’s climate control.

“There is no comprehensive public resource where you can look up whether a facility has air conditioning,” Ovienmhada notes. “Even in air-conditioned facilities, prisoners may not have regular access to those cooling systems, so our measurements of the outside temperature may not be far off.”

Heat factors

Their analysis found that more than 98 percent of all prisons in the U.S. had an average of at least 10 days in the summer that were hotter than any previous summer, for any given location. Their analysis also revealed that the prisons that were most exposed to heat, and those that experienced the hottest temperatures on average, were primarily located in the U.S. Southwest. The researchers note that the Southwest, with the exception of New Mexico, is one region that does not have universal air conditioning requirements in state-run prisons.

“States run their own prison systems, and there is no uniformity in data collection or policies regarding air conditioning,” Wood said. He noted that while there is some information on cooling systems in some states and individual prisons, the data is generally sparse and too inconsistent to include in the group’s nationwide study.

Although the researchers were unable to include air conditioning data, they did consider other facility-level factors that can exacerbate the effects of outdoor heat. They looked through the scientific literature on heat, health effects, and prison conditions and focused on 17 measurable facility-level variables that contribute to heat-related health problems. These included factors such as overcrowding and understaffing.

“We know that when you’re in a space with a lot of people, it feels warmer, even if there’s air conditioning in that environment,” Ovienmhada said. “Staffing is also a big factor. Facilities that don’t have air conditioning, but are still trying to mitigate heat risk, may rely on staff to distribute ice or water every few hours. If that facility is understaffed or has negligent staffing, that can increase people’s susceptibility to hot days.”

The study found that prisons with any of nine of the 17 variables had statistically significantly higher heat exposures than prisons without those variables. Moreover, if a prison exhibits any of the nine variables, it may exacerbate people’s heat risk through the combination of increased heat exposure and vulnerability. The variables, they say, can help state regulators and activists identify prisons that should be prioritized for heat interventions.

“The prison population is aging, and even if you’re not in a hot state, every state has a responsibility to respond,” Wood points out. “For example, areas in the Northwest, where you would generally expect moderate temperatures, have experienced a number of days of increasing heat risk in recent years. A few days a year can still be dangerous, particularly for a population with reduced ability to regulate their own heat exposure.”

This story is republished courtesy of MIT News (web.mit.edu/newsoffice/), a popular site with news about MIT research, innovation, and education.