How Will Milwaukee Mitigate the Danger of Future Heat Waves?

The city wasn’t prepared the last time time a heat wave hit, but new warning systems could help prevent future deaths.

One sweltering summer night, a seven-month-old, en route to the emergency department in Milwaukee, died from heat-related respiratory failure. Her body couldn’t regulate her temperature while keeping her oxygen levels up. Compounding the tragedy, her family had been trying to install an air-conditioning unit the very night she died.  

This heart-wrenching story, along with several other cases reported by the Centers for Disease Control and Prevention read like admonishments, outlining stories of casualties of the 1995 heat wave that rocked the Midwest summer. Oversight, failure to prepare, and lack of adequate resources contributed to the deaths of more than 1000 people during the Midwest heatwave, which appeared over the southern Lake Michigan shoreline and parked for five days in July of that year. This unwelcome guest was announced, however. Local newspapers at the time recommended residents “slow down,” “think cool thoughts” and “use the air-conditioning” in preparation for the deadly weather. 

With this wave, nearly three decades ago, we were taught a lesson about the truly fatal impacts of heat on human bodies – especially nonwhite, urban-dwelling bodies. The National Oceanic and Atmospheric Administration (NOAA) submitted a report in 2018 that seemed to scold local leaders’ responses from Chicago to Green Bay, saying, “Given the advance warning, many, if not all, of the heat-related deaths associated with this event were preventable.” Still, three years after their findings were released, history repeated itself as though no lessons had been learned. 

In late summer 2021, a heatwave settled on the Pacific Northwest and sat there. Stifling, suffocating, and immovable, the high-pressure system created a “heat dome,” which settled from Oregon to Manitoba, Canada. Underneath this dome, warm air tried to rise. Finding nowhere to go, it stagnated before being forced back down, only to be met by more heat trying to rise. This push of air masses against one-another directly above cities like Portland, Oregon created a “block” – a stationary mass of air that prevents other air from moving in. News outlets made analogies to the lids on cooking pots to explain the inescapable and unending sauna. While maybe metaphorically helpful, the implications were insidious: In that lidded pot were real humans being cooked. Current estimates put the excess death toll somewhere between 800-1,200 people. They lost their lives in 2021 to heat. 


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These heat waves, as well as others across the globe, remind us that we are, perhaps, less prepared and more vulnerable to the steady, lethal force of hot air than we think. A combination of fragile human physiology, concrete cities that amplify heat’s power, and changing climate patterns have led to tragic deaths over the last few decades.  

As climate change impacts the frequency, duration, and intensity of these events, we should understand why and how to prepare. Bottom line: Heat kills more than any other weather-related event (barring some extreme outliers like Hurricane Katrina). 

On average, about 700 people die from heat-related causes every year, creating the most deaths in the U.S. of all weather-related mortalities. Better warning systems and technology have improved our ability to warn residents in advance. These warnings focus primarily on protecting the most vulnerable: the elderly, the young and the ill. But it turns out that heat can get the best of any of us. In fact, according to the Wisconsin Heat Network, “Ten percent more people die, on average, in Milwaukee, on a hot, dry day than on a typical summer day.” The body simply isn’t designed to endure extreme temperatures. 

Human bodies maintain their temperatures within a very narrow set of degrees—about 97 to 99 degrees Fahrenheit. This is overseen by the hypothalamus—somewhat of an event coordinator in the brain. When the hypothalamus senses things are getting too hot, it sends a signal to the cardiovascular system: Cool your jets. Blood vessels expand, bringing heat toward the surface of the skin. Because blood is also responsible for carrying oxygen around the body, this consequently diverts it. If diverted for too long, ischemia occurs. Ischemia is the technical term for a lack of oxygen to the organs, and when the heart experiences it, it goes into cardiovascular arrest: a heart attack.  

Larry Kalkstein, President of Applied Climatologists, Inc. and Chief Heat Science Advisory for the Arsht-Rockefeller Foundation Resilience Center, said heat is more devastating to the human body than we realize, “It’s not just heat stroke. Heart attacks spike during heat waves. Regular strokes spike during heat waves, and respiratory failure spikes during heat waves.”  

In Portland, during the heat dome, 79-year-old Penny Clark’s family reported to the Wall Street Journal that this was exactly what happened to her – she died in the ambulance of heart failure after heat exposure. Heat will shunt oxygen away from vital organs, and it also breaks down cells, allowing toxins to enter and pathogens to take over. The overworked hypothalamus also sends signals to trigger cooling mechanisms like sweating, but eventually, the body can’t keep up with the demand. The demand depends on the environment. If the person can get to somewhere air-conditioned, for example, that can help. Sometimes the environment is just too darn hot.  

Enter wet bulb temperature.  

We commonly hear about heat-index and humidity. When the meteorologist tells us it’s 80 degrees out but it feels like 87, that’s the heat index. Another, less common, term is wet bulb temperature, which, in one of science’s uninventive moments, got its name from literally wrapping a wet towel around the bulb of a thermometer. As the water evaporates out of the towel, the thermometer bulb cools and the temperature lowers. This is the wet bulb temperature, and it’s important because the water evaporating from the towel is much like sweat evaporating off skin. 

The wet towel is like sweat-soaked skin. Sweat works to cool the body through evaporation—as the water evaporates off the skin, the skin cools. But if it’s too hot out for too long, eventually the atmosphere will have absorbed as much evaporation as it can handle. The tipping point is a wet bulb temperature of 90 degrees Fahrenheit. At this temperature, sweat won’t evaporate fast enough, and our internal heat will climb. The sweat becomes useless with potentially fatal consequences. 

With higher wet bulb forecasts on the horizon, air-conditioning will become an absolute necessity in most of the US. However, these use up electricity and lead to higher utility bills while contributing to more greenhouse gas emissions. Not to mention, as previous heat waves have shown us, our infrastructure is unprepared to handle the greater stress on the electric grid. Air-conditioning use and hot temperatures both stress the grid, causing it to fail. Power outages occurred while heat continued to climb. This is especially problematic in urban areas like Milwaukee.  

Urban areas are both less capable of handling the need and more vulnerable to the stress that heat waves create. Elizabeth Berg, a PhD candidate at the Nelson Institute for Environmental Studies at UW-Madison who studies heat mortality said urbanscapes can completely alter temperatures from the ground to the atmosphere, making cities – even small, less populated ones – hotter than suburban and rural areas. This is surface heat exposure creates an “urban heat island effect.” City asphalt, buildings, and concrete essentially raise temperatures, sometimes by as much as 10 degrees, creating the exact wrong conditions that lead to heat mortality. These conditions disproportionately impact nonwhite, poor city dwellers. Berg discussed the striking results her team found when they looked at Milwaukee heat-related deaths. “The risk of elevated mortality is double for Black populations in Milwaukee than non-Black in the same conditions,” she said.  

In the stifling city heat wave of 1995, an 82-year-old Milwaukee woman died in her two-story home. Although she used a fan to fend off the warmth, she kept her windows and doors locked out of fear for her safety. Her thermostat crept to 90 degrees Fahrenheit overnight. Her tale exemplifies what researchers at the University of North Carolina Chapel Hill found in 2021, “People with an income below the poverty line have a significantly higher exposure than people with an income above twice the poverty line.” Their homes are already hotter, and they do not have the means to cool them – whether out of fear for their safety or a dearth of resources. With expected climate change bringing longer, hotter bouts of summer weather, it’s likely a matter of seasons before we see the next big heat wave or heat dome settle in, creating more chaos on the most vulnerable and under-resourced parts of the country.     

 It sounds serious, and it is. But there are solutions. Thanks to improvements in awareness and a greater understanding of the danger, cities are taking heat seriously. Kalkstein has helped to create a new tool that is being piloted for use in Milwaukee and Madison to better warn residents about heat events. Rather than looking at temperature alone, Kalkstein and his fellow researchers look at air masses. “Air masses are comprehensive,” said Kalkstein. “You’re looking at the whole picture: the temperature, the humidity, the cloud cover, the chance of rain, the wind.”  

By combining this encompassing look as well as an algorithm that tells him how deadly these kinds of air masses historically been, Kalkstein’s tool can be used by organizations like the National Weather Service to deliver more advanced warnings. Milwaukee’s Office of Emergency Management Director, Paul Riegel, said that this should help the city better prepare. They might be able to open more cooling centers than they otherwise would on, say, a cloudy warm day that might not have set off alarms before Kalkstein’s tool. 

The Center for Climate and Energy Solutions recommends short-term fixes like opening cooling centers during extreme heat in vulnerable areas and planting more trees and greenspaces to absorb some of the heat that bounces back into the atmosphere during the summer months. Berg agrees with these solutions. “There are both simple ways to extend greenspace and technological solutions,” she said. “Changing the materials that we build with or even repainting roofs to reflect more light – there are lots of ways we can create pockets that are much, much cooler in neighborhoods that currently have no remedies.”  

That, in combination with long-term goals like infrastructure improvements and lowering the greenhouse emissions which lead to hotter temps in the first place, will help. If we act now, we can avoid tragic CDC reports reminding us that we’ve, once again, failed to learn a life-or-death lesson.