As an overheated nation edges into autumn and the hope for cooler temperatures, researchers and clinicians are taking stock of what has been the hottest summer on record and the toll it’s taking on public health.

How bad was it? The National Oceanic and Atmospheric Administration reports that the average temperature in June-August 2026 in the contiguous US was 75.6 °F, the highest average since the government began keeping records 132 years ago, breaking the record set in 1936 by 0.4 °F. Daytime maximum temperatures averaged 88.6 °F across the contiguous US, also a record.

“It sure feels like it’s getting hotter. July and August have been a pretty rough couple of months,” said Jeffery Metzger, MD, MBA, chief of emergency services at Texas-based Parkland Health in Dallas.

So far in 2026, the Texas health system has recorded 96 emergency room (ER) arrivals with heat-related complaints, including 46 in August alone. Parkland Health recorded 64 such arrivals in all of 2025.

“When you look at our numbers, we always see an increase in heat exposure during this time of year, and this year does look like it’s probably worse than the past few years,” Metzger said.

The Heat Is On

The Environmental Protection Agency projects that the US will warm faster than other parts of the world in the years ahead, having already risen about 60% more than the global average since 1970. Extreme heat days — with temperatures hitting 95 °F or higher — and multiday heat waves are expected to become more frequent, to cover more geography, and to last longer.

Moneesh Bhow, MD, an emergency physician at Banner Estrella Medical Center in Phoenix, said his department’s diagnoses for heat-related illnesses are on the rise, in part, because of a growing awareness by staff of the threat.

Phoenix this year recorded its second-hottest summer. By late August, The Big Saguaro had already booked 100 days of temperatures that either reached or surpassed 100 °F. That included 39 days above 110 °F and 9 days above 115 °F.

“We’ve put a lot more focus and attention on heat-related illnesses, Bhow said. “We have a triage process that is based upon the symptoms that they present. It could be just vomiting and diarrhea and you may think that it’s just a simple case of viral gastrocarditis.

“But especially when it’s hot out, we dig a little bit deeper to see if it could it be heat related. We’re asking what work they do, what environment they live in. Certain medications may precipitate it as well. We definitely dig a little bit deeper into it, especially in this time of the season.”

The Silent Killer

Rising temperatures have prompted a re-evaluation of the effects heat is taking on public health. As recently as 2018, the CDC estimates on heat-related mortality were remarkably under-counted, averaging only about 700 deaths per year. 

Quinn Adams, PhD, a climate epidemiologist with Boston University’s Center for Climate Control and Health said, her models suggest that since 2018 the US has averaged about 9000 heat-related deaths each year, and that still could be an under-count.

Low-balling the death toll “is not all that surprising to me because of the way that our death classification system works,” said Adams, who recently teamed with NPR in a 2-year study to assess heat-related mortality.

“If somebody goes into the ER with a heart attack and ends up dying, the underlying cause might have been of heat,” she said. “But in the ER, you don’t see that side of it. The classification is heart attack.”

“These are things that slip through the cracks all the time because you can’t readily attribute this to heat if you don’t do a thorough death investigation,” she said. “Without explicit evidence, they’re not going to make that call based on a hunch. ‘Oh, it was maybe hot outside today.’”

“That makes it quite tricky. That’s why they call heat the silent killer.”

A Difficult Diagnosis

Metzger said determining heat’s role in ER visits is problematic, given the care venue’s fast pace, high volumes, limited access to medical histories, and patients’ often inability to communicate.

“There’s no good way to say definitively why someone is coming in with altered mental status or with low blood pressure, and what role the heat played on it,” he said.

“If someone is outside at some block party and they’re drinking and they come in altered and their body temperature is elevated, we don’t know how much of that is electrolyte stuff. We don’t know how much of that is just the heat itself,” he said. “We don’t know how much of that is the alcohol. There’s no really good way to tease out which one of those is the major factor.”

Bhow agreed.

“From an emergency department point of view, you’re dealing with information just at that moment,” he said. “If somebody is critically ill, they can’t relate a history to you. You may not be able to get that background history to know they were working outside, it was 110 degrees, and then they passed out. What we’re seeing is that EKG at that moment and it looks like a heart event.”

Even postmortem reviews may not uncover heat’s role in a patient’s death, Bhow said.

“The hard part is that there is no standardized test to say, ‘Hey, this patient was 105 degrees 20 minutes or an hour ago.’ There’s no way to identify that,” he said. “I don’t even know if you moved it out and went to a medical examiner’s office that they would be able to determine that. It’s really more based upon clinical and context clues.”

Body Bags, Misters, and Kiddie Pools

When physicians determine that heat is playing a role in a medical emergency, the immediate treatment is pretty clear: Cool down the patient, stat!

Fortunately, fast-acting, efficient, and inexpensive options are readily at hand. For years, emergency physicians and emergency medical technicians have zipped overheated patients into body bags packed with ice.

“A body bag sounds morbid, but you’re able to contain the ice as it melts,” Bhow said. “It makes for a cleaner environment and it allows them to cool down faster.”

At Parkland Health, Metzger said another simple treatment uses evaporative cooling where “you mist the patient and have a fan blowing on them,” he said, a process likened to cooling stations found at hot-weather public venues such as sporting events and concerts.

“And then there are some aftermarket options,” he said. “We just trialed a body-shaped, sort of kiddie pool that cycles cool water through it. Then we have endovascular techniques, where we can put a catheter inside a vein, and it pumps cool water through a catheter and cools the body from the inside out.”

Have A Plan

Heat-related illnesses are nothing new for hot spots such as Dallas and Phoenix. For ERs in the Sun Belt, identifying and treating overheated patients is routine.

“We experience this all the time, so we don’t have a three-ring binder on a shelf that we pull out when this happens. This is just what we do down here,” Metzger said.

For parts of the nation that don’t contend with a lot of extreme heat, Metzger advises “the biggest thing is having a plan.”

It doesn’t have to be particularly complex, “like using a body bag and knowing how you’re going to need buckets of ice,” he said. “Think ahead and make sure that you’ll know what to do when you see these patients come through the door.”

The experts cited in this article had no relevant disclosures.