Rise in heat-related deaths shows the impact of climate change ‘measured in human lives’

Key takeaways:

• The yearly number of heat-related deaths more than doubled between 1999 and 2023.
• Physicians should educate patients on heat-related dangers and communicate heat mitigation efforts, a researcher said.

Heat-related deaths have increased significantly over the past 2-plus decades, more than doubling between 1999 and 2023, data from a research letter published in JAMA indicate.

The percentage of deaths attributed to heat-related causes has risen steadily since 2016, according to the investigators.

The research “is descriptive in nature and serves really as a first step,” Jeffrey T. Howard, PhD, an associate professor of public health at the University of Texas at San Antonio, told Healio.

“I have an interest in understanding how climate change is affecting health. I had been reading some articles about the so-called ‘temperature anomaly’ that started in 2023 —the warmest year on record — and it led me to wonder if we could actually detect an impact in heat-related deaths in the United States,” he said. “So, that led to this investigation.”

In the analysis, the researchers assessed the change in heat-related deaths from 1999 to 2023 using data from the CDC’s WONDER platform. For each year, they determined age-adjusted mortality rates (AAMRs) per 100,000 person-years for heat-related deaths.

The results showed a total of 21,518 deaths from 1999 to 2023 recorded as heat-related, with an AAMR of 0.26 (95% CI, 0.24-0.27).

Howard and colleagues found that the number of health-related deaths increased from 1,069 (AAMR = 0.38; 95% CI, 0.36-0.4) in 1999 to 2,325 (AAMR = 0.62; 95% CI, 0.6-0.65) in 2023. This equaled increases of:

• 117% in the number of heat-related deaths; and
• 63% in the AAMR.

The lowest number of heat-related deaths in a year occurred in 2004, with 311. Meanwhile, researchers reported a high of 2,325 heat-related deaths during 2023.

The AAMR increased by 3.6% annually (95% CI, 0.1%-7.2%) during the study period. Howard and colleagues observed a nonsignificant decrease in the AAMR from 1999 to 2016, followed by an increase of 16.8% a year (95% CI, 6.4%-28.2%) from 2016 to 2023.

Howard said the most interesting finding may be the clear change in trajectory his group observed.

“There is a famous climate-change graph called the ‘hockey stick,’ which has been very widely circulated that shows global temperatures roughly stable over decades, then an abrupt change with a steep upward slope over the last couple of decades,” he said. “The graph in our letter is a new hockey stick graph, only this time it is measured in human lives.”

Howard highlighted several implications for policymakers.

“Local leaders should have heightened awareness of the risks and, especially for cities in high-risk areas, should take steps to increase their local surveillance efforts, adjust their heat mitigation communications strategies and invest in additional heat mitigation/prevention efforts such as cooling centers, hydration centers and so forth,” he said.

As for primary care providers, “these results suggest ongoing efforts to educate patients about the dangers and communicate heat mitigation efforts to their patients, especially those with higher risk for chronic diseases,” Howard told Healio.

He hopes the research “sound[s] the alarm” and raises awareness about the change in deaths.

“I think what is needed now are more detailed analyses of where these deaths tend to occur, which a large portion are in Arizona, California, Texas and Nevada,” he said. “More work should be done to understand at a more detailed level in these geographic areas the risk factors in those specific states.”