In the St. Louis region, heat has killed at least one person this year. In Omaha, Nebraska, a child died last month after being left in a hot car. Outside of Chicago, a person died in a hot prison in June.
Heat is the deadliest climate-driven disaster in the U.S. according to the National Weather Service, killing more people last year than hurricanes, tornadoes and floods combined. But experts say official estimates of deaths due to hot temperatures are likely low.
“This is a country-wide and even a worldwide phenomenon of the undercounting of heat deaths,” said Daniel Vecellio, an assistant professor at the University of Nebraska at Omaha who studies the impact of climate on human health.
Extreme heat can cause a multitude of life-threatening health effects. Some are explicitly related to high temperatures and have it in their name, like heat stroke, said Dr. Alok Sengupta, an emergency medicine physician and the chief medical officer at Mercy Hospital St. Louis.
“Your body has mechanisms to cool itself, but once it overwhelms that process, it actually then kind of turns into a cycle that you aren't able to sweat and so then you can't cool yourself,” Sengupta said. “And then it raises body temperatures to the point where you get neurologic symptoms, such as things like headache, dizziness, weakness.”
But in other cases, heat exacerbates an underlying condition. For example, if someone has an existing heart issue, heat exposure can trigger a potentially deadly heart attack. These instances may not show up in official counts of heat deaths, Sengupta said.
“If heat illness or heat exhaustion or heat stroke isn't listed as a cause, you're not going to know that that was a contributing factor,” Sengupta said. “So it's definitely under-reported.”
Data discrepancies
Even official data tracking heat deaths can reveal reporting gaps. The National Weather Service reported 207 heat fatalities in 2023, while the U.S. Centers for Disease Control and Prevention says approximately 1,220 people die from heat every year.
The NWS also reports state-specific numbers. In 2023, the agency does not list any heat deaths from Missouri, but the Missouri Department of Health and Senior Services said 34 people died from heat-related illness that year. A spokesperson for Missouri’s DHSS said it may not be possible to compare numbers between agencies because of “differences in case ascertainment and classification.”
Health officials don’t always have the resources or time to investigate if heat contributed to a death, which leads to undercounts, Vecellio said.
“There are some places that just don't have the capacity in their public health departments or in their coroner’s offices to be able to do so,” Vecellio said.
In the absence of direct references to heat on death certificates, Vecellio said health officials can also look at excess deaths compared to average numbers to see if there were more deaths than normal during a heat wave.
But there are places that are doing a better job tracking the deaths. Vecellio pointed to innovations in some parts of Arizona, which have become national models for counting heat with methods like recording temperature data at the location someone died. All of that is important because more information about how deaths happen could prevent similar deaths in the future, Vecellio said.
More heat
As officials struggle to get a clear picture of heat deaths, climate change is bringing more potentially deadly weather, said Trent Ford, Illinois’ State Climatologist. Heat is one of the Midwestern weather hazards that is most closely tied to climate change, he said.
“What we've seen across the Midwest, including in Illinois, is an increase in the frequency of extreme heat since the turn of the 20th century,” Ford said.
The Midwest is experiencing its own flavor of extreme heat, Ford said. The average high temperature in Illinois hasn’t changed much in the last 100 years. Instead, overnight temperatures in the Midwest are warming, which doesn’t give homes and humans a chance to cool down. The region is also experiencing an increase in dangerous humidity, which disrupts the primary way humans cool themselves: sweat.
“That sweat just kind of sits there on your skin, and it can't be evaporated in the air as easily because there's already so much water vapor in the air above you,” Vecellio said.
Despite the worsening heat, Vecellio said scientists are still trying to determine if there is a direct link between climate change and an increase of heat deaths. That’s in part because as climate change brings more dangerous heat, people are also putting more adaptation measures in place. More people are installing air conditioning, several states have adopted worker protections, and there’s an increasing awareness of the dangers of heat, Vecellio said.
The best way to guard against heat-induced health effects is to limit time outside on hot days, Sengupta said. If that’s not possible, Sengupta suggests monitoring for symptoms like heavy sweating, goosebumps with heat and eventually dizziness, fatigue or nausea. If that starts happening, he said to get out of the heat, drink fluids and electrolytes, and seek medical help if it gets worse.
This story was produced in partnership with Harvest Public Media, a collaboration of public media newsrooms in the Midwest. It reports on food systems, agriculture and rural issues.
