Debbie Willson holds a photograph of her son, Adam Willson, who died in June 2024. Debbie is certain his death was influenced by heat, but his death certificate does not mention it. These omissions are common across the country and lead to an underestimation of the impact of heat, according to research by NPR and Boston University. Ryan Kellman/NPR hide title toggle title Ryan Kellman/NPR An NPR investigation finds that heat kills thousands of Americans every year. But official records radically underestimate the number of victims. In this series, we bring you stories that reveal why this happens and what can be done. Heat is killing thousands more Americans each year than official data suggests, and the U.S. health care system is struggling to document its often silent role. Debbie Willson is well aware of how a death can go unnoticed. Debbie and her son, Adam Willson, lived in a sun-scorched neighborhood in Tucson, Arizona. Both were born with a genetic disorder called DiGeorge syndrome, which caused heart problems. Adam also had cerebral palsy and some developmental delays, so Debbie cared for him full-time, even after he became an adult. Despite those challenges, Adam was thriving by the time he reached his 20s, Debbie says. He was obsessed with movies, especially horror ones. “Freddy, Jason, Michael, Chucky, all those horrors,” he says, laughing: He loved them. “I tolerated them.” He worked at a local movie theater and showed him a horror script he had written in his free time. He was looking for film programs to apply to. DiGeorge syndrome also made both Adam and Debbie very sensitive to heat. Too much heat exposure could cause seizures and strain their already stressed hearts. On really hot days, even going outside would be too much for the two of them, Debbie says, so they would retreat to their house and hope the swamp cooler would keep them comfortable. Debbie Willson cared full-time for her son, Adam, until her death. Both Debbie and Adam were born with DiGeorge syndrome, which made them sensitive to heat. But in southern Arizona the heat is omnipresent. Ryan Kellman/NPR hide caption toggle caption Ryan Kellman/NPR But in southern Arizona, the heat is inescapable. This is especially true as climate change raises temperatures. Between the 1950s and 1970s, Tucson could expect less than one day of temperatures above 110 degrees each year. In this decade, that average had skyrocketed to nine days per year and reached 18 in a single year. The city’s annual number of extremely hot days (days whose highs are greater than 95% of temperatures from 1991 to 2020) has increased by almost an entire month since 1970. June 2024 was no different: hot. Almost every day that month was over 100 degrees, with 14 days at 105 or higher. Halfway through the month, the swamp cooler broke down. But, as always, money was tight and Debbie couldn’t afford to fix it. The house was heated and stayed warm. Debbie was anxious, especially when Adam started having problems with his heart. He immediately made an appointment with his doctor. The morning of that date, Debbie came into Adam’s room to wake him up. But his body was cold and limp. Adam had died overnight. He was 27 years old. How Heat Deaths Are Undercounted Adam Willson’s death is likely one of thousands of heat-related deaths that go uncounted in the U.S. each year. Federal records show that, on average, about 1,700 people died from heat-related causes each year in the U.S. between 2018 and 2025. But new research from NPR and Boston University finds that the number is likely about 9,000, or five times higher, and even that number may underestimate the deadly impact of heat. There are several reasons why those deaths don’t show up in state or national death counts, says Quinn Adams, an epidemiologist at Boston University and lead researcher on the NPR-BU investigation. Heat is rarely the only cause of death, and often aggravates existing health conditions. Because heat does not leave an obvious mark, its role in a person’s death is often not included on the death certificate, even when it is a key contributing factor. “We know that during extreme heat events, many people die because they have preexisting conditions,” Adams says. “The heat is working to worsen these other conditions and cause people to die faster than they otherwise would.” Like many cities in the United States, Tucson, Arizona, is experiencing more extreme heat due to human-caused climate change. The city used to expect less than one day of temperatures above 110 degrees each year. Now, the average is nine. In 2024, it broke a record of 112 days at over 100 degrees. Ryan Kellman/NPR hide title toggle title Ryan Kellman/NPR “You Have to Ask the Question” Debbie is sure the heat played a role in Adam’s death. She says this was also believed by the emergency response team that arrived at her house that terrible morning. Adam had been sweating in the overheated house for days, stressing his heart. But his death certificate only says “Unknown Natural Causes.” That’s not unusual, says Brian Drummond, an emergency room doctor in Tucson. It can be complicated and time-consuming to determine whether heat contributed to death. As in Adam’s case, there are often multiple contributing factors. When there is no single obvious culprit, doctors may mark the cause as unknown. In other cases, doctors may record only the most obvious cause of death, for example, a heart attack. The question is: What caused that heart attack? Medical experts know that heat exposure can stress the heart so much that it can trigger a fatal event. But doctors like Drummond, along with medical examiners and coroners who certify deaths, need conclusive evidence to establish that link, he says. That evidence is often invisible unless explicitly sought. “If I never ask a patient, ‘Were you exposed to extreme heat?’ or ‘Do you have the ability to cool where you live?’, I would never diagnose them with a heat-related illness unless their temperature was 105,” Drummond says. Debbie Willson did everything she could to keep her house cool. He kept the blinds closed and the refrigerator on as much as he could. But the month Adam died, the refrigerator broke down. Debbie’s brother was surprised when he came to visit, she says: “He says, ‘It feels like it’s 130 degrees in here!'” Ryan Kellman/NPR hide caption toggle caption Ryan Kellman/NPR Even for someone like Drummond, who is well-versed in the ways heat can influence medical problems and knowledgeable enough to look for them, it can be difficult to determine exactly whether it played a role in a specific case. Either way, he says, to more accurately track heat deaths, you first “have to ask the question.” “Without it, you will never get to the real answer.” Investigating heat deaths Pima County, Arizona, where Adam lived, has in recent years made it a priority to ask that question and identify whether heat plays a role in the deaths. He has trained death investigators in the medical examiner’s office to uncover the faint clues of heat’s influence on a death. Did a call to an air conditioning technician go unanswered? Was the deceased taking any medication that suppressed his ability to feel heat? Perhaps they had a health condition like diabetes or heart disease that made them vulnerable to dehydration or a heart attack if their body became overworked. Adam Willson loved horror movies. When it was too hot outside, he and his mother would sit on the couch and watch movie after movie to pass the time. Adam had even written a horror script and was looking to apply to film school. Ryan Kellman/NPR hide caption toggle caption Ryan Kellman/NPR These strategies have improved Pima County’s ability to detect heat-related deaths. It’s a place where official records largely matched the findings of NPR-BU’s analysis. However, stories like Adam’s suggest that both may underestimate the problem. In Pima County and across the country, many deaths never make it to the medical examiner’s office. In Arizona, for example, deaths are automatically investigated if they are suspicious or violent, involve diseases of public health concern, or if the person who died did not have a doctor. Adam’s death, like many others, did not fall into any of those categories. Debbie could have called the Pima County medical examiner to request an autopsy, but she didn’t see the point, she says: Adam was dead either way. Instead, he called the primary care doctor who had cared for Adam for years. He certified the death of Adam. That simple process is standard practice in many parts of the country, especially when someone has a known medical condition and, like Adam, is under the care of a doctor. Changing these practices to further investigate the role of heat is not easy, says Drummond, the Tucson doctor. “People are interested in this, but it’s difficult,” he says. “It takes time, money and commitment.” Arizona is well aware of its heat problem. Cities like Tucson and Phoenix are experimenting with ways to help protect their residents. But they are fighting an uphill battle as climate change makes the heat more dangerous. Ryan Kellman/NPR hide caption toggle caption Ryan Kellman/NPR Without changes in such practices — for medical professionals, coroners, medical examiners and all those who collect information about deaths — the true cost of heat will be drastically underestimated, says Adams, an epidemiologist at Boston University. That has consequences. When we don’t know the magnitude of the problem, Adams says, we can’t adequately address it. Debbie Willson wonders if her son would still be alive if there had been services available to help people like her cope with the heat. For Debbie, the loss of Adam is still painfully recent. His son is gone: his brilliance, his sharp humor, the way he brought the whole family together, is gone. The horror script he had written will remain on the shelf forever. “I had my whole life ahead of me,” Debbie says. “He had a lot of things planned for himself.” Edited by Rachel Waldholz and Sadie Babits
