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On a scorching May 2020 day that topped out at 95 degrees, Austin resident José Mario Calles reported to his landscaping job.
A lawsuit later filed by Calles’ family recounted what happened next: The 51-year-old, who financially supported his wife and kids in El Salvador, fainted. He was rushed to the hospital and spent two nights being treated for a heart condition and diabetes, both known to make people more vulnerable to heat.
The lawsuit claims that his employer did not report the incident to the Occupational Health and Safety Administration or to its worker’s compensation insurance carrier as required by law. The father of six returned to work without the necessary medical clearance, according to the lawsuit, hefting 40-pound bags of mulch. Twelve days after his initial collapse, he suffered a heart attack at a job site and didn’t wake up.
The Travis County Medical Examiner found the cause of death was myocarditis, an inflammation of the heart muscle. The autopsy did not mention heat.
Last year was the hottest year on record for the state. And the heat was particularly deadly: State records report that 365 people died directly from heat, the most heat-caused deaths on record. The count rises to 562 when including deaths where heat was a contributing cause.
Climate change is causing hotter days and nights, which put extra stress on the human body. The problem is likely to only get worse.
Yet deaths related to heat are almost certainly undercounted in Texas and nationwide, according to experts. Accounting for heat’s role in a death is notoriously difficult because of the subjectivity and complexity of the process. For example, doctors or local officials who fill out records listing the cause of death might not consider the weather on the day a person died or if a person routinely worked in the heat.
“The health impacts (of heat) are a little bit more subtle,” said Sameed Khatana, assistant professor of medicine at the University of Pennsylvania and a cardiologist. “They can be delayed. And trying to tease apart whether a death or an adverse health effect occurred due to the temperature is quite challenging.”
During a recent visit to Austin, Douglas Parker, assistant secretary of labor for occupational safety and health, called heat “the most dangerous weather phenomenon that workers face.”
Failing to accurately count how many people are dying from heat-related causes leaves officials unable to grasp the scope of the problem and work more directly to fix it, said Andrew Dessler, professor of atmospheric sciences at Texas A&M University.
“A lot of the argument over climate change is: Why should we care if temperature goes up a degree?” Dessler said. “And this is one of the reasons why we should care.”
Community organizers, scientists and academics say the lack of public information and understanding about heat deaths makes it hard to mount an effective local response to what they consider a public health crisis.
“How do you tackle a problem if you don't know the size of the problem, if you don't understand the breadth and the depth of the problem?” said Gregory Wellenius, an environmental epidemiologist and professor on environmental health at Boston University.
A data analysis by The Texas Tribune found that Texas likely failed to account for many heat-related deaths between 2013 and 2019. During those years, the state recorded 777 heat-related deaths. The Tribune’s estimate — calculated by comparing how many people died on abnormally hot days with how many people would have been expected to die during more average weather — found that 998 deaths were associated with heat during that period in the 41 most populous of Texas’ 254 counties.
Texas counties with medical examiners take varying approaches for how they document heat-related deaths. For example, Dallas County reports all deaths in which heat was suspected to be the cause of death or a contributing factor. In Nueces County, which includes Corpus Christi, an official said they don’t track heat-related deaths at all.
“Deaths are investigated differently depending on where people die. We don't really have a federal death investigation system, every state runs a different death investigation system. And so the whole thing is pretty fragmented," said Gregory L. Hess, a chief medical examiner at Pima County in Arizona, which includes Tucson.
That means cases like Calles’ can fall through the cracks because heat wasn’t cited by the medical examiner as a possible contributor to his death. It’s not clear whether the medical examiner considered heat as a factor. In Travis County, only deaths that are directly caused by heat are recorded as heat-related.
John Escamilla, a McAllen attorney who sued Calles’ employer on behalf of the family and specializes in workplace accidents and injuries, said more people are coming to him seeking legal help for cases involving workers who have suffered heat-related injuries. The landscaping company BrightView, which purchased the company where Calles worked, declined to comment.
“I don't think employers consciously put their workers at risk. I think they're ignorant or they don't really care,” Escamilla said. “But these summers are getting more and more intense for longer periods of time.”
A silent killer that’s difficult to diagnose
For some deaths, the role heat played is clear: In June 2023, a 68-year-old man was found dead on the couch in his Fort Worth home. A death investigator found that the air conditioning was broken and the temperature inside the house was 91 degrees.
The same month, a 28-year-old man was found having "seizure-like activity" in a Fort Worth strip mall parking lot. His core body temperature was measured at 108 degrees at the hospital. His muscles broke down, his brain swelled and there was evidence of liver failure, according to an autopsy.
On Aug. 25, 2023, a 48-year-old woman was admitted to a suburban Houston hospital with a body temperature of 108.1 degrees. She’d sat outside for an hour, according to an autopsy.
Heat kills people when the body cannot cool itself and a person doesn’t take action soon enough to cool their body. In hot weather, the body redistributes warm blood to the skin to protect internal organs. Sweat evaporates, cooling the skin and lowering the temperature of the blood beneath.
But if it’s too hot, a person is exerting themselves physically or remains in the heat too long, the body can heat up faster than it’s able to handle. The heart races as it goes on overdrive to circulate blood throughout the body. Blood pressure drops.
If the person doesn’t drink water and escape from the heat, the next phase is heat exhaustion, marked by weakness, profuse sweating, headaches or dizziness. Without adequate treatment, the situation can progress to heat stroke, when body temperature can spike to 103 degrees or more and vital organs like kidneys, heart and brain become starved for oxygen — a potentially deadly situation.
“People often are unaware that heat is starting to cause [health] problems, and, by the time they're aware of it, it can be too late,” said Kristie Ebi, a professor and expert on heat’s health risks at the University of Washington Center for Health and the Global Environment.
[How to stay safe in the Texas heat]
But often, figuring out the role heat played is more difficult. Experts refer to heat as a silent killer because the harm it causes isn’t necessarily clear or sudden.
Teasing out whether heat contributed to a death becomes subjective. Experts who fill out death forms — including physicians, medical examiners and local justices of the peace, who all have varying levels of training — have different thresholds for when they feel they have enough information to list heat as a direct or contributing factor to a death.
It also takes time and effort to track down information about the circumstances that preceded someone’s death to look for clues that may point to heat as a contributor. Was the person suffering in a hot home? Living under an overpass? Playing tennis in the heat?
“It also depends on peoples’ need for a level of precision,” said Scott Sheridan, a geography professor at Kent State University in Ohio who obtained a Ph.D. in climatology. “And that's where I think heat tends to be one of the most difficult to convey. … We all think about the runner that collapses in the heat, or some very obvious case, but the vast majority of cases just aren't that obvious.”
And even with an autopsy, the picture might still be murky, said Bob Anderson, a branch chief in the division of vital statistics at the U.S. Centers for Disease Control and Prevention, which assigns codes to the state’s death data so it can be analyzed.
Say an elderly person with heart disease who gardens frequently is found dead outside — did heat play a role?
“So it can vary according to the quality of the death investigation that's done, and how much information is gleaned,” Anderson said. “But even the best death investigation won't always tell you whether heat played a role or not.”
In Arizona, medical examiners hunt for heat deaths
Experts say the model for how to more thoroughly investigate and count heat deaths is Maricopa County, Arizona, in the Sonoran Desert, which is home to around 4.6 million people, including in Phoenix, and regularly reaches temperatures of 110 in the summer. The county medical examiner’s office has been working since 2006 to catch every death that could have been related to heat, Chief Medical Examiner Jeff Johnston said.
Their reviews are thorough: When pathologists receive a case, they do an autopsy and they consider medical history, information from the place the person died and recent events to determine if heat contributed to the death, Johnston said.
“The devil’s in the details really with these,” Johnston said.
Johnston knows his office isn’t catching every case — that would require investigating every single death, even when heat isn’t suspected, which is cost-prohibitive. But he argues they have one of the most robust systems in the country for detecting heat-related deaths. In 2018, they even coined a category for them: environmental heat exposures.
Assistant Medical Director for the Maricopa County Department of Public Health Nick Staab said local officials use this data to inform their strategies for how to help Maricopa County residents stay cool.
Maricopa County used the data to support doubling the county’s network of cooling centers operated by local groups and cities to more than 100 and extending the hours at some of them to include weekends. Arizona 2-1-1 coordinates free transportation to the centers.
They’ve also partnered with community health workers, or promotoras, to supply information on how to beat the heat and find cooling centers in English and Spanish.
Officials map where deaths occur and gather demographic and behavioral data to understand who is dying and why they were at risk.
“We strongly believe in public health that all of these deaths are preventable,” Staab said, adding, “We’re trying to tell this story. We’re trying to define extreme heat as a public health emergency so that we can get additional funding, additional resources to bring to our high risk population.”
In Texas, most of the biggest urban areas have medical examiners to investigate deaths. But those offices don’t investigate every death: Texas law requires an investigation in circumstances such as a suspected suicide or homicide, or when a person dies within 24 hours of being admitted to a hospital.
Dr. Jessica Dwyer, a medical examiner for Dallas County, said tracking heat-related deaths is inherently complex because no single method fits all cases. A death involving drug ingestion on a hot day might be classified differently depending on the medical examiner’s judgment. Dwyer said this variability stems from differences in training, office protocols, and personal experience.
“Standardizing it becomes a little difficult because not every case is the same," Dwyer said.
Some people are left more vulnerable to the heat than others. This includes older residents, children, and people with chronic diseases. People experiencing homelessness and migrants trying to cross vast stretches of brushland on foot also contend with the dangers of heat more than people who spend much of their time indoors.
On the outskirts of El Paso, 12 people died from heat during the summer of 2023 while trying to immigrate through the blazing Chihuahuan Desert. Many more died in neighboring Sunland Park, New Mexico.
“Every summer, we've really tried to shoot for zero deaths,” said Graciela Ortiz, who coordinates the Extreme Weather Task Force in El Paso. “I am going to tell you, though, we blew the record out of the water last year. I was shocked.”
In Dallas last year, Rose Jones, a public health professional, said she was shocked to hear stories from friends who worked in an emergency room about homeless patients arriving with third-degree burns from falling asleep on the pavement. It unsettled her so much that she decided to quit her job with an urban forestry group to start a consulting practice focused on protecting people from extreme heat. She knew people such as undocumented workers and prisoners would suffer first.
“These are all marginalized groups so in general it’s not going to get a lot of attention. People will just go into their air conditioned homes,” Jones said.
In San Antonio, Lotus Rios saw the heat’s danger grow. The 45-year-old community leader, indigenous activist and mother of two runs a small food pantry where needy neighbors can eat for free. Over the years, life has become more difficult as the city’s tree cover gave way to more concrete, and summer temperatures grew warmer.
“People used to be able to survive with a box fan in the window, that’s not the case anymore,” Rios said. “Fans are not helpful when it’s 104.”
She sees a lot of suffering in her line of work. But nothing was as hard to bear as the story of Albert Garcia.
Garcia lost both legs to frostbite while living outside when Winter Storm Uri plunged Texas into subfreezing weather for a week in February 2021. Later, Rios and others helped secure shelter for Garcia. But he suffered incontinence and felt abused by shelter workers. A year later, he was back under an Interstate 35 overpass.
Garcia used drugs. He liked to preach from the Bible and make jokes. He often made Rios laugh.
In August 2023, after more than 50 consecutive days of triple-digit weather, Garcia died beneath the overpass where he slept. The local news website Deceleration told his story in a series of articles.
When journalist Greg Harman, founder of Deceleration, went to the site of Garcia’s death, several days later, he measured the temperature at 114 degrees.
Garcia’s autopsy report, obtained by Deceleration, said he died of a drug overdose. He had heroin in his system. But it also noted his last known use was on the morning of Aug. 11, nearly a day before his death — and overdose deaths typically happen soon after someone uses drugs.
“He was somebody,” Rios said. “He didn’t have to die the way he did.”
Last week, Harman and 500 other signatories filed a petition to the San Antonio City Council, asking it to produce a count of heat fatalities in the area.
On Monday, after repeated correspondence with the Tribune, the public information officer for Bexar County provided a count of hyperthermia fatalities. It showed 12 deaths in 2023, five times the annual average for the 10 prior years (not counting heat-related mass casualty events in 2017 and 2022 when dozens of migrants died locked in hot tractor-trailers).
Disclosure: Texas A&M University has been a financial supporter of The Texas Tribune, a nonprofit, nonpartisan news organization that is funded in part by donations from members, foundations and corporate sponsors. Financial supporters play no role in the Tribune's journalism. Find a complete list of them here.
OUR METHODOLOGY
We conducted our analysis of excess deaths largely following a similar analysis published by the Los Angeles Times in 2021, with guidance from Ariel Karlinsky, an economist and statistician at Hebrew University. The methods were reviewed by other experts, including an epidemiologist and a climate scientist.
We built a model that predicted how many people would be expected to die under normal circumstances and used it to estimate the number of excess deaths on summer days where abnormally high heat indexes were recorded. For this analysis, we looked at the 41 most populous counties in Texas, which covers about 85% of the state’s population. We found 998 excess deaths on abnormally hot days between 2013 and 2019. We excluded 2020, 2021 and 2022 from this analysis because of a high number of excess deaths caused by the COVID-19 pandemic. The 2023 mortality data was not yet available at the time of this analysis.
This analysis helped us calculate the number of deaths attributable to heat, but also has its limitations. First, the mortality data we used includes deaths by any cause, except mass shooting deaths. We subtracted those after seeing unusual spikes in deaths in counties on days when a mass shooting happened. But it is difficult to control for every factor, which could result in overcounts in our estimates. Additionally, the model only accounts for deaths on the days where the heat index was abnormally high — even though in some cases heat victims die days or weeks after heat exposure. This would contribute to undercounts in our estimates.
To calculate abnormally hot days, we looked at maximum heat indexes recorded on each day in every county from 1981-2010. We classified days as abnormally hot if the heat index was in the top 10% for that day at that location during the 30-year span.
Because the number of excess heat deaths is relatively small compared to overall deaths, the estimates come with a wide margin of error, Karlinsky said.
Mortality data was obtained from the Texas Department of State Health Services. The heat-related official counts were current as of July 16. The meteorological data is from CDC's Heat & Health Tracker. Read our more detailed methodology here.
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Correction, : A previous version of this story included an incorrect location for attorney John Escamilla’s practice. It is in McAllen.
