Extreme heat is killing people in prisons across the United States, according to  a new study published in the academic journal PLOS ONE. The research provides some of the first epidemiological evidence of the link between the climate crisis and prison mortality in the nation with the highest incarceration rate in the world.

The study examined deaths in both state-run and privately run prisons during the hot summer months of June, July and August between 2001 and 2019. Researchers found that a 10-degree temperature increase above the average correlated with a 5.2 percent increase in deaths — or a 6.7 percent increase among prisoners with heart disease.

To Julie Skarha, the study’s lead author, who recently finished her doctorate in epidemiology at Brown University, “The biggest surprise was that the highest increase of mortality was in the Northeast,” she told Grist. The study found that a two-day heat wave meant a mortality increase of 21 percent in the Northeast, compared to 0.8 percent in the Midwest, 1.3 percent in the South, and 8.6 percent in the West.

Also startling was the link between heat and suicide in prisons nationally. In the three days following an extreme heat day, the researchers noted a 22.8 percent increase in suicides.

To the researchers as well as advocates for people who are incarcerated, the findings hint at deepened desperation among prisoners in the summer, even in states not known for their heat. To Skarha and others, the data is a call to action for policymakers. “There should be more regulation around what kind of temperatures people are exposed to in these settings,” Skarha said. “If temperature regulation isn’t happening in these settings, then they shouldn’t be operating.”

Read the full article about climate change and prison deaths by Alleen Brown at Grist.