Howard Ehrman has seen his fair share of gruesome sights in his 56 years as a physician. But he’ll never forget working at Cook County Hospital 30 years ago when a heat wave sweeping the country settled over northeast Illinois.
“That was the worst experience of our lives, all of us who were doctors, because we literally could step out the door … and we could see these trucks going by, and we knew what they were: refrigerator trucks filled with bodies going down the street on Harrison to the Cook County medical examiner,” he said.
Between July 12 and 15, 1995, thousands of Chicagoans sought care at area hospitals. Not all of them made it home.
“We had lots of people who came into the emergency room who were too far gone to save,” said Ehrman, who worked at the hospital, now known as Stroger Hospital, for 17 years.
Only many days after the start of the heat wave would the magnitude of the tragedy begin to sink in, as newspaper articles and nightly news reports tallied hundreds of deaths across Chicago.
Ultimately, 739 people died, mostly elderly residents, people of color and those who lived alone and had no one to check in on them. The toll was catastrophic, making it the deadliest weather event in Illinois history and redefining the city’s emergency response and disaster preparedness.
As climate change increases the frequency and length of this kind of lingering, humid heat in the region, many scientists and health care workers are wrestling with the question: Could another extreme heat crisis arise in Chicago?
“If we take the exact same meteorological event we had in 1995 and plop it down in today’s society, I don’t think we’d have 700 premature deaths,” said Daniel Horton, a professor at Northwestern University and co-lead of a working group that is developing a heat vulnerability index for Chicago. “Because AC is much more prevalent … and people are much more aware of the danger of heat.”
Since 1995, messaging around the dangers of extreme heat has improved in Chicago, and air conditioning has become more common. But today, there are still numerous challenges to ensuring the public is protected during extreme weather. Among these:
- Only about 30% of single-family homes in Chicago have central air conditioning, compared with 76% of homes nationwide, according to an analysis of Cook County data by Elevate, a nonprofit that studies energy efficiency.
- For those who do have air conditioning, rising cooling costs can present a major obstacle.
- The potential exists for more power outages, either from strain on the electric grid or increasingly severe storms that could knock out power.
- The city has a large network of cooling centers, but service gaps remain overnight, on weekends and during holidays.
- The abundance of buildings and asphalt traps high temperatures, amplifying the effects of heat by more than 8 degrees for 1.7 million of its 2.7 million people. The concentration of green spaces in white, wealthy neighborhoods means residents in poorer areas have little relief.
- Heat deaths remain hard to track, obscuring the extent of the danger posed by heat. Advocates and experts say guidelines are inconsistent for medical officials determining whether heat is listed as a cause of death, a contributing factor or even at all.
An assistant health commissioner for the city of Chicago under Mayor Harold Washington and later an assistant professor at the University of Illinois Chicago until 2022, Ehrman has in recent years taken on an activist role with groups like the Little Village Environmental Justice Organization. In 2020, he co-founded the People’s Response Network, a group that is pushing to expand the city’s health network and social services.
While preparedness for heat waves has improved since 1995, the way Chicago counts heat deaths is “subjective,” Ehrman said. He wants the city to gather and release data from hospitals about whether the mortality rate rises during heat waves, rather than publicizing only those deaths that have heat listed as a factor.
“If Mr. Smith dies at home or on the way to Cook County Hospital or at the hospital, and he’s got four or five major underlying conditions, there will almost never be a doctor who will put heat on the death certificate,’’ Ehrman said. “So that’s the huge problem. Heat-related deaths (are) a massive undercount.”
Silent killer
Experts often refer to extreme heat as a silent killer: It sneaks up on people, and its symptoms can be subtle. And that subtle but very real danger was on full display in July 1995.
“What happened — in terms of fatalities, especially — was kind of a slow evolution, a slow disaster,” said Mike Bardou, a warning coordination meteorologist at the National Weather Service office in Chicago. “The effects of heat on the body are cumulative. It’s not necessarily an immediate thing.”
On July 12, after days of continuous rain, a musty heat spread across the Chicago region and temperatures soared with a record-high heat index of about 126 degrees. It had climbed, and stayed, well past the level required to trigger the city’s emergency heat plan. Instead of raising the alarm, city leaders waited three days before warning residents.
Mark Razter, a 28-year-old meteorologist less than a year into his job at the National Weather Service, was driving home from a weather conference in St. Louis that day. Nothing seemed unusual except that it was uncomfortably warm.
“Obviously, we knew it was hot,” said Ratzer, the only meteorologist currently working at the weather service who was also there 30 years ago. “But I don’t think anybody, going into it, had an appreciation for quite the severity that it was going to be.”
By the time officials declared a state of emergency and the rising number of heat deaths started dominating the news cycle, Ratzer said “the heat wave itself was over.”
Meteorologists at the local weather service office had a more limited approach to public messaging back then than they do now, Ratzer said: “We produce a forecast, and then we let the decision-makers do what they do with that information. We might issue a heat advisory or heat warning.”
He said the threat wasn’t visibly destructive like a tornado.
“Nothing journeying through, tearing down buildings,” he said. “It’s almost like no warning would have prevented some of those things; the whole system needed to change. Which it did.”
After the heat wave, the weather office started working much more closely with the city and including public health guidance in its forecasts.
“That kind of microcosm of change that occurred during the event, around messaging, is something that has very much taken hold — not just in Chicago, but globally, particularly with the advent of human-caused climate change,” Horton said. “We now know that extreme heat is the No. 1 killer, from an environmental health perspective.”
Heat waves kill more people in the United States than all of the other weather-related disasters combined, according to the National Oceanic and Atmospheric Administration.
Thirty years ago, extreme heat was rare in Chicago. In the years since, however, area residents have grown increasingly familiar with stretches of similar, sometimes even higher, temperatures and humidity that rival conditions from the 1995 event.
The heat index — a combination of atmospheric temperatures and relative humidity that determines how the heat really feels to the body — peaked at 124 degrees on the second day of the 1995 heat wave, and remained over 105 the other days. On Aug. 23-24, 2023, Chicago experienced its highest heat index since then, reaching 120 degrees. During another hot stretch a year later, the peak index was the same.
Most recently, during a three-day heat wave beginning the weekend of June 21, the heat index peaked at over 100 degrees.
-
Ava Montenegro, 9, plays in a splash pad in Chicago’s Humboldt Park, June 25, 2025. (Chris Sweda/Chicago Tribune)
1 of 54
Ava Montenegro, 9, plays in a splash pad in Chicago’s Humboldt Park, June 25, 2025. (Chris Sweda/Chicago Tribune)
Heat can also be particularly dangerous if it lingers. People die from extreme heat, Horton said, not necessarily because of acute exposure in the middle of the day, but because humid heat persists through the night, limiting the body’s ability to recover, rest and recuperate.
Summer nights have become warmer under climate change. In Chicago, while overall summer average temperatures have warmed by 1.7 degrees between 1970 and 2024, average overnight lows have increased by 2.5 degrees in that same period.
“It’s this long-term exposure to high heat and humidity, and no bodily breaks, that makes people really suffer and ultimately die because of it,” Horton said.
The vulnerability index that Horton’s team is developing aims to identify residents and communities who are particularly vulnerable to heat. It also seeks to help in the design of solutions to reduce residents’ risk, and to inform the city’s policy decisions and resource allocation to improve emergency response and preparedness.
To determine which Chicago residents are at the highest risk during heat waves, team members are studying factors that can worsen or alleviate someone’s experience of extreme heat. For instance, underlying health conditions like cardiovascular disease, diabetes or respiratory illness are linked to higher susceptibility to hotter weather. They are also asking: Who in the city has access to air conditioning? Can they afford to run it?
Lack of uniform definition
In July 1995, officials ruled 485 deaths as heat-related.
But health experts and climate scientists say the number is over 700, because death certificates underestimate the real number of people killed by heat and hinder a proportionate response.
According to a study of the Chicago event published in the American Journal of Public Health, “the heat wave appears to have contributed to 254 more deaths than were attributed by the Cook County Medical Examiner’s Office.”
“This is a problem throughout — I would say a global problem — that heat is not listed as a contributor,” Horton said. “It is incredibly rare for heat to be listed as the cause of death.”
In an August 1995 report, the Centers for Disease Control and Prevention said “a lack of a uniform definition for heat-related death across the U.S. results in substantial variation in the criteria used to certify such deaths.”
During a typical year, the Illinois Department of Public Health confirms an average of 15 heat-related deaths across the state, according to Graham Briggs, division chief of emerging health issues at the agency.
“That varies a little bit year to year, but we think that that’s a large underrepresentation,” he said. “There’s a lot of complexity, trying to understand how heat (drives) things like renal failure and cardiovascular disease and other stressors on the body.”
Heat is considered the primary cause of death when there are no other reasonable explanations, and when a person’s body temperature is 105 degrees or more when they die. However, if the temperature is not measured at or close to the time of death and the body has cooled down, it can be difficult to classify it as a heat death.
But heat is not often the sole or main reason people die; rather, it tends to be a contributing factor. Older people or those with cardiovascular disease are particularly vulnerable to extreme heat, according to Ponni Arunkumar, the chief medical examiner for Cook County.
“The heat is just a stressor that pushes them over and causes them to die,” she said.
At the county’s medical examiner’s office, labeling a death as heat-related entails a thorough investigation of many factors, including the surroundings: Was the person who died in a place with no air conditioning? Were the windows closed?
“We want to know the circumstances,” Arunkumar said.
Since 2015, when the county’s medical examiner’s office started keeping electronic records, 27 deaths among Chicago residents have been marked as heat-related; three of them died in typically colder months because they were exposed to malfunctioning heating systems. Heat is listed as the primary cause of death in only five cases, including those of three women who died at a Rogers Park senior living facility during a May 2022 heat wave because the heat had been kept on in the building and the air conditioning was broken.
Records also show 15 people have died since 2015 of cardiovascular disease made worse by hot weather. Another four have died of complications from drug and alcohol use, which interfere with body temperature regulation, complicated by exposure to heat.
But even when heat aggravates preexisting health issues, those circumstances might get overlooked by different agencies, Briggs said.
Still, he hopes that experts’ understanding of how many people actually die from heat, whether directly or indirectly, is improving with technological advances and thorough data analysis.
“Every year, we get a little bit better at the way that we report (heat) deaths,” Briggs said.
Climate dependent
While some ComEd customers experienced interruptions in July 1995, there is no record of widespread system failure, according to Mark Baranek, senior vice president of technical services at the company.
To relieve strain on the grid and reduce the possibility of greater outages, however, ComEd did implement some temporary outages, he said in an emailed statement.
George Goss, an expert on grid stability and professor emeritus of electrical and computer engineering from the University of Illinois at Urbana-Champaign, moved to Champaign in 1993. He said he’d be surprised if something similar happened today.
“I think we’re in a different position than we were 30 years ago,” he said, “but I would not deny that there’s a possibility.”
Nowadays, Gross said, electricity is very climate dependent.
“Not only in terms of generation — because now we use solar and wind — but also because (of) that kind of heat,” he said. “And particularly if it’s persistent, then it can cause all kinds of stuff.”
For instance, power lines can sag when the air around them isn’t cool enough. And if they touch each other or a tree, they can short-circuit or start electrical fires.
During periods of extreme heat, the risk of outages can rise. For instance, the grid may become overwhelmed from a large swath of the population running the air conditioning at the same time, or severe weather can knock down electrical infrastructure.
Briggs, from the Illinois Department of Public Health, said if severe weather coincided with a heat wave, it could put people at risk.
“If we did see loss of power in a large area over a sustained period of time — in a vulnerable population like assisted living centers … we could see a number of deaths,” he said. “Hopefully, we’re better prepared if we do see a nightmare situation.”
The Chicago area is not unfamiliar with dangerous combinations of severe weather and heat. In June 2022, a line of thunderstorms swept across the Midwest and part of the South, followed by a heat wave with indices over 100 degrees. Energy operators had to cut off electricity to customers — because supply couldn’t meet the growing energy demand — for 21 hours as a measure to prevent larger-scale blackouts. In northern Illinois, storms left 125,000 ComEd customers without power overnight.
According to climate science nonprofit Climate Central, 80% of all major power outages — affecting at least 50,000 customers or interrupting 300 or more megawatts of service — in the United States reported between 2000 and 2023 occurred due to weather; more than half of those were caused by severe weather, which includes high winds, rain and thunderstorms.
Over that same period of time, Illinois experienced 77 major power outages, of which 69 were weather-related, according to the U.S. Department of Energy. Between 2008 and 2017, most electric outages in the state occurred in July, each affecting an average of 624,486 customers.
Driven by climate change, accumulating humidity in the region has increased the intensity of severe storms and tornadoes. These represent a particular threat to above-ground transmission wires, transformers and utility poles, which transmit and distribute most electricity but are thus exposed and vulnerable to the elements. Where power lines are buried, flooding can also cause issues.
In a letter to the Chicago City Council and Mayor Brandon Johnson last September, the People’s Response Network called on the city to take public ownership of all electricity by ending its contract with ComEd, which they claim has “failed over and over again” to maintain infrastructure in Black and Latino neighborhoods, leading to blackouts even as electricity costs rise.
Each summer, ComEd presents emergency preparedness plans to the city of Chicago and the Illinois Commerce Commission. Preparations for heat waves include reviews of circuit loading, maintenance of generators to deploy, as well as plans for transformer failure and transporting key replacement equipment where needed.
“ComEd is prepared to ensure safe, reliable power during hotter and more humid heat waves,” Baranek said. “Investments made in the system over the last 30 years have improved the reliability and resiliency of the grid, while keeping an eye on affordability so customers can take action like running air conditioning and fans.”
The company has also invested in climate-resilient infrastructure, Baranek said, such as moving key circuits underground to reduce outages related to severe storms, as well as trimming and removing vegetation near power lines to protect them from debris in the case of a tornado.
According to ComEd, customers across Chicago experienced a 99.99% reliability rate last year, with 94% or more than 1.2 million local customers experiencing zero or one interruption.
“This is the best performance on record,” he said.
Stepping in
Today, city services have a more solid plan in place in the event of extreme heat, experts say. But community awareness of the impacts of extreme heat has also been heightened.
“In this heat wave, we’re checking up on each other,” said Linda Austin, who works as a senior liaison in the 16th Ward, during an extreme heat advisory on June 23. “If there’s someone who we haven’t seen in a while, we’re reaching out.”
Austin runs weekly meetings for seniors living in the Englewood area on Wednesday mornings. During heat waves, she said she encourages residents to check in on their neighbors daily to make sure they’re safe and healthy, and helps organize rides for seniors in the area if they need to get somewhere.
During the 1995 heat wave, many of the casualties were seniors who didn’t have family or neighbors to check in on them, especially those living in high-rise buildings where the heat was particularly intense.
“We had people in senior centers calling (for help), and some people didn’t have air conditioners or fans,” she recalled. “We always say, we will remember.”
Whether they’re organizing with neighbors in their wards or helping children and seniors professionally, more people now understand how to prevent heat stroke in their day-to-day lives by hydrating, staying in cool spaces and seeking medical help as soon as symptoms start to show up.
During the three-day heat advisory in June, at least 10 Chicago aldermen told the Tribune that they had a plan in place that was specific to their ward, with many providing water to residents or checking in on seniors during the advisory.
Members of the community also step in.
“I’m a librarian, so they’re really not supposed to be bringing any food or liquid, but I do let them bring in their water bottles as well, especially if I have a class coming in after they’ve been outside,” said Atondra Rouse, 63, a librarian at Turner-Drew Language Academy.
During the 1995 heat wave, Rouse lost her 3-year-old son, Geno, after a home-based day care provider left Geno and another child asleep in a hot car. The day care provider faced criminal charges and was sentenced to two years of probation.
Rouse said she was at her mother’s house picking up her then-5-month-old daughter when her husband called to tell her what had happened.
“When I got to my mother’s house, (my husband) called again, and he said, ‘He’s gone,’” she recalled. “He told me to come home because something was wrong with little Geno.”
Rouse said she takes extra care to stay out of the heat, especially during the hot summer months. In her role as a librarian, she works with students every day, and during hot days, she helps pass out water bottles to the students.
“I try, I try (to look out for them),” she said. “I love my kids.”
