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Officially, heat deaths are not very common in Colorado. The reality is more complicated.

Colorado sees only a handful of heat-related deaths per year, but the statistics don’t capture heat’s more pernicious effects

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Missy Anderson stepped out of the shade and into the building heat of another day in one of Denver’s hottest summers on record.

Anderson is an injury prevention coordinator at Denver Health, meaning she works to deter the kinds of accidents and events that often land people in the hospital. On this July day, that involved giving a demonstration on the health dangers that summer heat can pose. She had parked her SUV in the driveway in front of the hospital and stuck a thermometer inside. Next to the car was a sign displaying the result.

It was about 95 degrees outside. Inside, the temperature after just a few minutes had already climbed above 150 — hot enough to kill. In a few minutes more, it would hit 165.

“We don’t think a lot about heat in Colorado,” she said. “We usually think about cold weather because that’s what we’re known for.”

Missy Anderson, an injury prevention coordinator at Denver Health, gives a demonstration showing how fast a car can heat up on a hot day on July 19, 2022. The actual outdoor temperature was about 95 degrees, but the thermometer shows higher because it was in the sun. (John Ingold, The Colorado Sun)

Just going by the official numbers, the health impacts of high heat are not something we need to think a lot about in Colorado. There have been no hot car-related deaths reported in the state so far this year.

Last year, only five people in the state died from heat-related causes, according to death certificate data compiled by the Colorado Department of Public Health and Environment. That encompasses all deaths with heat stroke, dehydration or hyponatremia as a contributing factor.

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In 2020, there were six heat-related deaths in the state. Kirk Bol, the manager of CDPHE’s vital statistics program, wrote in an email to The Sun that the numbers from both years are a statistically significant increase over the 20-year average of 2.7 deaths per year.

Compared to the hundreds of heat-related deaths that are documented annually in places like Phoenix and Las Vegas, though, the numbers make it appear as if Colorado has little to worry about, even as summertime temps creep higher.

In 2020, the second-hottest summer on record for Denver and the one with the most 90-degree days, only about 300 people visited the emergency room in Colorado for heat-related illnesses and only about 40 people were hospitalized, according to CDPHE. Until recently, even official heat warnings have been rare in the state, due to Colorado’s traditionally low humidity and cool overnight temperatures.

But experts in public health and prevention, such as Denver Health’s Anderson, say those official numbers are missing the bigger picture.

All the different ways that heat harms

The problem with tracking heat-related deaths is that its most pernicious impacts typically leave no trace.

“I would consider heat to be a threat-multiplier, meaning it often puts other coexisting medical conditions in crisis,” said Dr. Jay Lemery, an emergency medicine specialist and the co-founder of the Program on Climate and Health at the University of Colorado School of Medicine.

The result is that when, say, a patient with cardiovascular disease shows up at the hospital during a heat wave, doctors typically see and address the medical issue. They don’t recognize the impact of heat that may have pushed the patient’s condition into crisis.

The same goes for patients with chronic diabetes. Or kidney disease. Or the elderly. Lemery calls these patients “physiologically vulnerable.”

“That little push off the cliff gets people in trouble and they’ll have exacerbations of their disease,” Lemery said.

Dr. Ryan Lawless, a trauma surgeon at Denver Health, gave an example of how this works. On a recent night, a patient came into the hospital who had been found lying on the floor at home. The patient had underlying medical conditions, which is what caused the hospitalization and what doctors focused on for treatment.

But how the patient ended up on the floor and what role a recent run of scorching temperatures had played in worsening the patient’s condition were not part of the diagnosis. Heat may have been the triggering factor, but it didn’t make the official statistics.

Accidents caused by dizziness from dehydration, asthma brought on by poor air quality during heat waves, falls caused by touching a hot hand railing and pulling back — none of those get filed as being heat-related.

“A lot of times, we think ‘medical problem,’” said Denver Health’s Anderson, a former emergency department nurse, “when in fact it may have been the heat.”

Preparing for even hotter summers

That heat-related health problems — both obvious and less so — will continue to get worse as the Earth’s climate warms due to human-caused greenhouse gas emissions is taken as a given by experts.

Colorado’s summers are getting hotter sooner and staying hotter longer, Anderson said. That means the window of time for heat-related health concerns is also expanding.

Dr. Jonathan Samet, the dean of the Colorado School of Public Health, said “epidemic heat” — the waves of extreme heat that draw most of the attention — could cause higher numbers of officially documented heat-related deaths in Colorado. That’s what happened on a 100-degree day this summer when a mountain biker died on a trail near Palisade called the Palisade Plunge after running out of water, a death the local coroner has classified as heat-related.

Riders descend the lower section of the Palisade Plunge, a 34-mile trail that drops 6,000 vertical feet as its winds off the Grand Mesa down to the Colorado River. (Joey Early / RockyMounts, Special to The Colorado Sun)

But long-term exposure to high heat will impact health in other ways. Samet mentioned research by Colorado doctors on agricultural workers in Guatemala with unusually high rates of kidney disease. Chronic dehydration caused by working in extreme temperatures is a prime suspect, he said, and climate change could expand how many workers are at risk across the globe.

In Colorado, neighborhoods where a lack of air conditioning and sparse shade cover from trees are the norm are especially at risk. So, too, are people who are homeless. On days when temperatures have soared to near 100, Denver this summer has opened recreation centers as cooling stations for anyone needing a break from the heat, something Samet said will need to become part of a normal, health-focused response to hot weather.

“Public health needs to be prepared both to alert the public and we need to be prepared to provide access to cool spaces for those who need them,” he said.

Mapping Colorado’s climate risk zones

While all of Colorado will experience impacts of climate change, the specific concerns aren’t evenly distributed.

To understand how climate change’s consequences will play out across the state, the Colorado Health Institute has launched an initiative called Acclimate Colorado. The idea is to map which concerns will be most prevalent in which places, and then help local officials understand how best to respond in their areas.

Some parts of the state are at risk for extreme heat — think the Eastern Plains and areas around Grand Junction.

A map from the Colorado Health Institute showing counties in Colorado most at risk from extreme heat, as defined by the number of days where the average temperature is above 90 degrees. Darker orange equals more extreme heat days, while darker blue equals fewer. (Provided by CHI)

Other areas, especially those in the mountains, are particularly vulnerable to major wildfires. And then there are underlying social and health circumstances that place some communities more at risk than others. Communities with higher rates of poverty, higher rates of non-English-speaking residents and higher rates of non-white residents may be at greater risk of suffering more due to climate change. The same goes for communities with higher rates of chronic illness.

A map from the Colorado Health Institute’s Health and Climate Index showing county rates of underlying health conditions that could be adversely impacted by climate change. Counties in orange have more health risks, while counties in blue have fewer. (Provided by CHI)

Karam Ahmad, a senior policy analyst at CHI who is working on the Acclimate Colorado project, said his organization hopes to create a Colorado “where communities are prepared to meet the emerging health challenges caused by a warming climate.” (You can dive deeper into CHI’s climate change impact maps here.)

One of the things that makes the CHI initiative unique is that it is not focused on trying to stop climate change from happening or to mitigate its effects. Instead, the organization made a conscious decision to think of climate change as a present-tense risk to health in Colorado, something that should be dealt with just like any other ongoing health crisis.

Lemery agreed that the medical and public health communities need to become better prepared for handling climate impacts like extreme heat and all the consequences they bring.

“Every year, I see this, and I get more and more scared,” he said. “It’s a palpable sense of something’s changing, something’s different and it’s not going to get better.”


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