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Heat deaths in the US will reach record levels in 2023, study says

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As global warming increases, heat-related deaths are also increasing in the United States, according to a new study that examined nationally reported data since 1999.

More Americans died from heat in 2023 than in any other year in more than two decades, according to the findings released Monday. Last year was also the world's hottest year on record, the latest grim milestone in a warming trend fueled by climate change.

The study, published in the American Medical Association's journal JAMA, found that 2,325 people died from heat in 2023. The researchers admit that this number is probably an underestimate. The study took into account a growing and aging U.S. population and found that the death toll is nonetheless alarmingly high.

“The current trajectory of warming and climate change is actually showing up in an increase in deaths,” lead author Jeffrey Howard, an associate professor of public health at the University of Texas at San Antonio, told USA TODAY. “This is something we hadn't measured before.”

Howard, along with researchers from the Uniformed Services University of the Health Sciences in Maryland and Pennsylvania State University, examined data from death certificates between 1999 and 2023. Deaths were counted if heat was listed as an underlying or contributing cause of death.

The number of reported deaths remained relatively constant until about 2016, when the death toll began to rise in what Howard, who studies the health effects of extreme weather, calls a “hockey stick” trend. The hockey stick analogy is used to describe global warming caused by climate change, which has seen temperatures rise at alarming rates in recent years.

Howard's study suggests that the death toll follows the same pattern. One important indicator is age-adjusted deaths per 100,000 people. This heat-related death rate has increased dramatically compared to the early 2000s, regardless of age or population size.

The upward trend seems to be strengthening recently. In 2022, 1,722 people died, with an adjusted rate of 0.47. But in 2023, there were 603 more deaths than the previous year, with an adjusted rate of 0.63, the highest rate ever recorded.

Deaths were not evenly distributed across the country. In an interview, Howard said deaths were mostly concentrated in traditionally hot regions: Arizona, California, Nevada and Texas.

The study is limited in that it classifies heat-related deaths by local authorities, which could mean that the true number of deaths is underestimated. It may also be biased as more people become aware of the deadly risks of heat. The study did not break down groups at risk. For example, people without air conditioning, people who live or work outdoors, and people with underlying health conditions are at higher risk of severe illness or death from heat.

Heat is often described as a silent killer, says Sameed Khatana, an assistant professor of medicine at the University of Pennsylvania and a cardiologist at the Philadelphia VA Medical Center who has studied reporting on heat deaths.

Officials are increasingly paying attention to heat when filling out death certificates, Khatana said. “I think there's a growing understanding of some of these subtleties that have been highlighted in research over the last few decades.”

Researchers like Khatana had previously called for improvements in the reporting of heat-related deaths.

The reporting of heat on death certificates varies across counties across the country, says Ashley Ward, director of the Heat Policy Innovation Hub at Duke University's Nicholas Institute for Energy, Environment and Sustainability. “Guidelines and standards need to be developed on how we determine whether heat is a factor.”

Researchers of the study, published on Monday, called on local authorities to invest in expanding access to drinking stations, public cooling centers and additional buildings with air conditioning.

Even in 2024, the sweltering heat of the summer months has not stopped. It is unclear how the death toll compares, but there have been several heat waves across the country in recent months.

Phoenix, for example, set a new record for the number of days with temperatures above 100 degrees Fahrenheit, and the region continues to extend that record, said Mark O'Malley, a meteorologist with the National Weather Service in Phoenix. Sunday was the 91st consecutive day of temperatures above 100 degrees at the city's Sky Harbor Airport.

In July, California and New Hampshire experienced the warmest July on record this summer, and 19 other states also had one of the ten warmest Julys on record, according to the National Oceanic and Atmospheric Administration.

Globally, three consecutive days in late July were the hottest on record, surpassing the previous July's record. NOAA estimates the probability that this year will be the warmest on record at about 77%.

“Overall,” Howard said, “it seems like things are getting worse, not better.”

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