Texas was among the hottest places on Earth this month as a heat wave brought misery from Mexico to Florida. While residents across the region struggled to stay cool, the extreme heat took a particularly severe toll on those who could least protect themselves, particularly incarcerated people.

According to the Texas Tribune, at least nine people in Texas prisons died as temperatures in the state reached triple digits. These deaths illustrate the unique dangers incarcerated people face when extreme weather hits, dangers that will only grow as heat waves, droughts and hurricanes become more frequent due to climate change.

The exact impact the heat had on incarcerated people in Texas this month, let alone the death toll, is unclear because the state prison system hasn’t classified a death as heat-related in more than a decade. But a 2022 study found that between 2001 and 2019, roughly 13% of deaths in Texas prisons during warm months could be attributed to extreme heat. That estimate is 30 times higher than the number of heat-related deaths in the general U.S. population.