Amid Brutal Heat Wave, Officials Stress Health Risks of Hot Nights

High nighttime temperatures can do more than just disrupt your sleep, experts say.

Much of the United States is baking amid an unusually severe June heat wave, with more than 150 million people under some sort of heat advisory. The unrelenting heat wave started in the Mountain West over the weekend and has since descended upon the Midwestern and Eastern U.S., where high humidity is making temperatures topping 100 degrees Fahrenheit feel even hotter. 

Even at night, people can’t escape the unforgiving heat, which poses a particularly high health risk. 

The level and duration of the heat is rare for this time of year “with little to no overnight relief, and affects anyone without effective cooling and/or adequate hydration,” the National Weather Service said in an advisory Monday morning.

During a heat wave, it is crucial for people to cool down at night to reduce their core body temperature and reduce the physiological burden put on them during long, sizzling days. But a growing body of research shows that hot nights are becoming more common with climate change—and not just during a heat wave. 

These increasingly uncomfortable nights could have drastic impacts on your sleep and overall well-being, experts say. 

Record-Breaking Heat: The triple-digit temperatures currently boiling much of the Midwestern and Eastern U.S. can be attributed to a high-pressure system forming a ridge in the atmosphere known as a heat dome. It’s shattering daily-high temperature records across the country, from Mitchell, South Dakota (104 degrees on Saturday), to Minneapolis (96 degrees the same day). A road in Missouri literally buckled under the heat, sending cars soaring over the impromptu speed bump. 

Roughly 10 percent of the U.S. could see temperatures reach 100 degrees or higher today, including major cities such as New York and Philadelphia. Officials are warning individuals to take heat health risks seriously. 

“Don’t wait until you feel sick. Heat builds. It compounds. It kills quietly,” New York City’s Emergency Management agency wrote in a post on X. “This is the deadliest weather threat we face in New York City — treat it that way.” 

As I wrote about recently, research suggests that fans alone cannot help cool you down in temperatures above 95 degrees. Experts agree that securing access to reliable air conditioning is the single best way to avoid heat stress, but millions of people across the country do not have this luxury. Compounding the problem, many farmers and contractors are required to work outside for their jobs, exposing them to unsafe heat for hours on end. 

But people can at least rely on the chilly night air to cool them when the sun goes down, right? In many cases, the answer is no, especially as climate change accelerates. 

Nighttime Sizzle: During the day, heat is absorbed by clouds and moisture in the atmosphere, as well as human-made surfaces like asphalt roads and buildings. Once the sun goes down, this built-up heat radiates back out, swaddling people in an invisible and unwanted blanket after a sweaty day in the sun. 

“It’s very stressful on the body,” Brian Hurley, a meteorologist at the federal Weather Prediction Center, told The New York Times. “You’re not able to cool down, especially if there’s no ventilation. If you don’t have cooling mechanisms at home, it’s hard to get that relief.”

This nighttime problem can exacerbate heat wave deaths, particularly among unhoused people, older populations and individuals with pre-existing medical conditions. Many cooling centers across the country close in the late afternoon or evening, leaving visitors with fewer options for air conditioning overnight. And research finds that air conditioning itself releases excess heat into local environments, which can increase local nighttime temperatures in cities. 

Perhaps unsurprisingly, high nighttime temperatures can also negatively impact your sleep, which has trickle-down impacts on overall health. 

A 2024 report by an independent group of scientists known as Climate Central found that climate change has exposed 2.4 billion people from 2014 to 2023 to an average of at least two additional weeks per year of nighttime temperatures over 77 degrees. In some regions, data shows that nights are heating up faster than daytime temperatures. 

A separate study analyzed sleep data from around 47,000 adults in 68 countries and found that on nights that exceeded 86 degrees, people slept roughly 14 minutes less than they would on cooler nights. This heat-driven sleep loss could add up to 44 hours a year, The Washington Post reports. The scientists found the sleep-loss problem is worse for women, residents of lower-income countries and older adults. 

And new research revealed that global warming is also severely increasing the risk of sleep apnea events, when breathing stops and starts while people rest, NPR reports. 

In a nutshell, climate change is keeping us awake at night—literally. 

“We often don’t talk about climate change impacts on quality of life,” Christian Braneon, a climate scientist, told Inside Climate News in 2022 when discussing the sleep-loss study.

“Folks won’t necessarily die during every extreme weather event or every heat wave, but their quality of life is being compromised,” he said. “And this could exacerbate chronic illnesses, and ultimately lead to shorter life lifespans and … other challenges for people.”

Cover photo:  In June 2025, a severe heat wave hit the Midwestern and Eastern United States. Credit: Lokman Vural Elibol/Anadolu via Getty Images