Another heat wave is hitting the U.S. Here's what you need to know

Extreme heat is coming this week in many parts of the United States. The Midwest and Northeast in particular will see weather that puts them in the National Weather Service’s highest heat risk category — when lack of cooling or hydration can put almost anyone in harm’s way.

It’s a new labeling system for the NWS, which launched the experimental rating at the end of April with the Centers for Disease Control and Prevention in response to the growing danger of extreme heat. Last year was the hottest in 2,000 years here in the Northern Hemisphere.

“Many people do not realize how deadly extreme heat can be,” Jennifer Wang, the executive director of the Yale Center on Climate Change and Health, said in an interview with STAT last month. The heat risk index aims to highlight that link, basing its thresholds on a combination of local temperature and mortality data.

It’s just the first heat wave of the summer, with more likely ahead. If you need evidence to convince any stubborn family members that, no, they aren’t immune to extreme heat and, yes, we should put the AC in the window, STAT has you covered.

How do we measure extreme heat?

Some experts say that the U.S. is lagging behind other nations when it comes to both recognizing the risk of extreme heat and providing resources to address it.

The heat index — or the “feels like” temperature, which takes humidity into account — is commonly used to gauge heat stress on the body. But some experts argue that we need to move away from the heat index as a way of measuring risk, and instead use the wet bulb globe temperature, which assesses risk using wind speed and solar radiation in addition to temperature and humidity. Wet bulb globe temperature is measured by putting a thermometer in the sun, covered by a wet cloth. This differs from the heat index method, which utilizes a thermometer in the shade.

Some experts also believe that, on top of new measurements, we need a new system of warning people about extreme heat. Heat warnings are issued based on the probability of high heat, but people may experience poor health outcomes at a lower temperature than what triggers a warning. These systems often look at simply whatever the peak temperature is for a given day, but health impacts are also linked to high overnight temperatures, especially for vulnerable populations — one factor the new NWS tool takes into consideration.

What can the heat do to you?

It starts at birth. Many studies have shown that heat waves are associated with an increased risk of preterm birth. One recent paper analyzed more than half of all births in the U.S. between 1993 and 2017, finding that in the days after a heat wave, preterm births increased by 2%, and early births by 1%.

Perhaps the biggest health risks during heat waves are to our cardiovascular health. When the body is suffering under extreme heat, the heart begins pumping faster to distribute boiling blood out to extremities like fingers and toes, and away from sensitive organs. Heat stroke occurs when the body fails to cool itself down, and there’s also a risk for heart attacks, strokes, or heart failure in high heat.

A study last year found that between 2008 and 2019, extreme heat was linked to more than 1,600 excess cardiovascular deaths like this each year in the U.S. And the authors predicted that these deaths could increase by as much as 233% annually as temperatures continue to rise due to climate change.

Heat can also put your heart into “oxygen debt,” according to a study published earlier this month. About 60 participants in the research wore NASA-designed wetsuits that raised their internal temperatures. One-third of the oldest, least healthy participants had blood flow blockages. But even the younger and healthier participants showed reactions to the heat at surprisingly mild temperatures, researchers said, which has grave implications for extended exposure to heat in the real world.

And if all this is stressing you out, some experts believe there is likely a link between rising temperatures and mental health as well.

“The rates of suicide, depression, anxiety, and substance abuse are skyrocketing. And it’s not just because of climate change, but we know that anytime this population is asked about climate change, it is clearly a source of severe distress,” John Balbus, director of the climate change and health equity office for the Department of Health and Human Services, said in an interview with STAT last year. “People are deciding not to have children, people are worried about their future.”

What can be done?

Maybe someday we’ll all get prescriptions for AC, but today is not that day. Not enough people currently have access to air conditioning, and this is just one of the factors experts are considering when looking toward a future of even more extreme heat.

There’s no federal heat standard to protect outdoor workers from extreme heat, which leaves states and local governments to figure out their own approaches to this pressing public health issue. Last year, the Miami-Dade Board of County Commissioners voted on such a proposed standard. It would have been the first comprehensive local heat standard for outdoor workers in the country, going beyond requiring rest breaks and giving local officials regulatory teeth in a realm that lacks real oversight.

But it didn’t pass, and months later, the state issued a law preventing local municipalities from issuing such standards. This type of preemption law also exists in Texas, where more than 300 people died from heat last year.

On top of needed policy changes, experts are also calling for more acknowledgement of climate change and extreme heat within the medical field, including increased education for clinicians on how to best help their patients stay safe in extreme heat. Last year, a survey of more than 450 clinic workers in the U.S. found that 77% do not have the knowledge or tools to implement climate change preparedness at work, but over 80% were interested in education and training on how to protect patients. The HeatRisk launch at the end of April also included new guidelines from CDC for providers to manage heat’s impact on patient health.

The latest standard of care for extreme heat in hospitals is sort of an eerie one: immersive cooling in a body bag filled with ice and zipped to about shoulder level. These bags can cool a person twice as quickly as traditional methods, and take up little space.

At home, there are a few practical options. If you have access to an AC, that’s great, but many people don’t. Electric fans are a great option — if you heard that they may not be safe, fear not. A study in 2019 found that recommendations against these devices weren’t based on any scientific evidence.

“The idea that we should be recommending, ‘Oh, well, you should get an air conditioner,’ that’s a bit of a privileged kind of recommendation,” Ollie Jay, an associate professor in thermoregulatory physiology at the University of Sydney in Australia, said in an interview with STAT about the study that year. “We should be thinking about more ecologically valid solutions for people who find themselves in a situation where they can’t afford these types of interventions.”