Amid soaring temps, heat-related deaths have more than doubled since 1999

As 55 million people in the U.S. Midwest faced heat alerts on Monday, research published in the peer-reviewed Journal of the American Medical Association showed that heat-related deaths in the country rose 117% between 1999 and 2023.

"The current trajectory that we're on, in terms of warming and the change in the climate, is starting to actually show up in increased deaths," lead author Jeffrey Howard, an associate professor of public health at the University of Texas at San Antonio, toldUSA Today. "That's something that we hadn't had measured before."

Using a U.S. Centers for Disease Control and Prevention platform, Howard and co-authors from Pennsylvania State University and the Uniformed Services University of the Health Sciences analyzed all deaths from those 25 years coded for "hyperthermia of newborn," "effects of heat and light," or "exposure to excessive natural heat" as either a contributing or underlying cause of death.

They found 21,518 deaths for the full period, with 1,069 in 1999. The lowest annual figure was in 2004 (311) and the highest was in 2023 (2,325). Last year was the hottest on record globally and scientists are already warning that this year is expected to continue that trend.

"As temperatures continue to rise because of climate change, the recent increasing trend is likely to continue."

Last year broke the record that was set in 2016—a year that's also significant in the new study: "The number of heat-related deaths... showed year-to-year variability, with spikes in 2006 and 2011, before showing steady increases after 2016."

Howard toldCBS News that "it is likely that continued increases in average temperatures, the number of 'hot days,' and the frequency and intensity of heatwaves could be playing a role" in the rise since 2016.

"There is also a social and behavioral component as well," he added, "including differences in access to air conditioning, outdoor work, the number of unhoused individuals, and things like that."

The researcher noted that Arizona, California, Nevada, and Texas had the highest heat-related deaths—which he said is "not terribly surprising because we know that these are some of the hottest regions in the country, but it does reinforce that the risk varies regionally."

The paper warns that "as temperatures continue to rise because of climate change, the recent increasing trend is likely to continue. Local authorities in high-risk areas should consider investing in the expansion of access to hydration centers and public cooling centers or other buildings with air conditioning."

The authors also acknowledged limitations of their research—including "the potential for misclassification of causes of death, leading to possible underestimation of heat-related mortality rates; potential bias from increasing awareness over time; and lack of data for vulnerable subgroups"—meaning the true death toll could be higher.

A legal memo published in June by the watchdog Public Citizen detailed how local or state prosecutors could bring criminal charges against oil and gas companies for deaths from extreme heat made more likely by the fossil fuel-driven climate emergency.

"These victims deserve justice no less than the victims of street-level homicides," said Aaron Regunberg, senior policy counsel for the group. "And this memo shows that prosecutors have a path to secure that justice, if they choose to pursue it."