Heat-related deaths spiked 117% in the US since 1999

As temperatures reach record levels in many parts of the US this week, emergency rooms are bracing for a new normal: More patients are becoming gravely ill because their bodies can’t take the heat.

Heat-related deaths in the US have been steadily increasing for years, a new study published in the medical journal JAMA shows — a 117% increase in heat-related deaths from 1999 to 2023, with at least 21,518 people dying in that period.

Using data from the US Centers for Disease Control and Prevention, researchers found the annual number of deaths varied from year to year before 2016, with spikes in 2006 and 2011. But after 2016, the study found a steady increase. On average, heat-related deaths decreased by 1.4% from 1999 to 2016, then increased by 16.8% each year from 2016 to 2023.

The authors say heat-related deaths are probably undercounted.

“The way that death certificates are filled out, the people that are filling them out don’t always know the full circumstances that led to the death. So we’re only probably scratching the surface of it,” said study co-author Dr. Jeffrey Howard, an associate professor of public health at the University of Texas at San Antonio. “The fact that you see this trend tells me that there’s probably many more deaths that are we just are unable to measure.”

Unlike a clear-cut cause of death such as a car crash, deaths from heat can be harder to identify.

But awareness of global warming’s threat to human health is increasing among some physicians, said Dr. Catharina Giudice, an emergency physician and climate change and human health fellow at Harvard University who was not involved in the study.

“When you’re filling out a death certificate, you make your best interpretation with the available information you have, and I think the more people are aware of climate change-related mortality,” Giudice said. “So there may be some bias of increasing awareness over time” contributing to the recent trend, she said.

And more people will probably continue needing emergency care for heat exposure. By the end of this century, more than half of the global population is projected to be exposed to weeks of dangerous heat every year, according to a 2022 study. This makes even common activities like taking a hike in the Grand Canyon, going for a run in gym class or even just sitting on the couch without air conditioning potentially deadly.

Extreme heat is the No. 1 weather-related killer in the US, according to the World Meteorological Organization, but experts say it’s a phenomenon that often goes under the radar. Unlike with a hurricane, there are usually no dramatic pictures to remind people about the dangers of heat.

How heat kills

Heat can kill in at least 17 different ways, many related to heart and breathing problems. Some groups of people are more vulnerable to its effects, including small children and the elderly, whose bodies don’t regulate temperature as well, along with people with certain underlying medical conditions and people who have overweight or obesity.

Heat-related deaths may also include suicide, drowning and homicide, phenomena that could not be captured by this study.

Howard hopes that studies like this can bring more awareness of the issue, prompting more steps to avoid what are ultimately preventable deaths.

“I think this should be a real wake-up call to say ‘this really does warrant more attention,’ especially in areas of high risk,” Howard said.

Public health experts have recommended that governments invest in infrastructure that can help lower temperatures, like planting shade trees and installing covered bus stops. There are even cool pavement coatings that can lower surface temperatures when applied to asphalt.

Other suggestions have included making money available to put more air conditioners in schools and help people with limited incomes with costly air conditioning bills, as well as creating more cooling shelters and mobile cooling centers that can give people a break from the heat.

The new study found a disproportionate number of heat-related deaths in four states: California, Arizona, Nevada and Texas. “These are all hot areas, so you may expect that, but so much more could be done to plan for these hot days,” Howard said. “I hope this will spur further action.”