After a record-hot summer, the heat-fueled hurricanes that recently struck North Carolina and Florida raise more alarms for the future of health and vitality on a rapidly warming planet. LDI Fellows Sameed Ahmed M. Khatana, Ashwin Nathan, Lauren Eberly, Jagadeesh Puvvula, and colleagues are among those concerned. 

In their recently published study, the team sought to understand the pressing implications of climate change on mortality in the U.S. In previous work, Khatana estimated that by mid-century (2036-2065), heat-related cardiovascular deaths in the U.S. could rise by up to 233% as climate change intensifies the frequency, duration, and severity of extreme heat.

Khatana and the team found that extreme temperature days are associated with 8,249 deaths per year, based on data from 2008 to 2019. Looking ahead, they project that extreme heat days could result in about 19,349 deaths per year under a lower greenhouse gas emissions increase scenario, or as many as 26,574 deaths annually in a higher emissions scenario. That’s an increase of 134% or 222%, depending on the scenario.

Black and Hispanic adults are expected to bear the brunt of this increase. 

The team believes this is the first study to examine extreme temperature-related deaths across all contiguous parts of the U.S.—rather than a selection of cities—as well as projected changes across subgroups of age, sex, race, ethnicity, and regions. 

Here’s more from Khatana about this work:

Tell us about the study and what you found.

Khatana: The study looked at how deaths associated with extreme temperatures (both hot and cold) in the contiguous United States are projected to change from now to the middle of the 21st century (2036-2065) under higher and lower greenhouse gas emissions increase scenarios. We found that although the current number of deaths associated with extremely cold days is higher than the number associated with extremely hot days, by mid-century, the number of extreme cold-associated deaths is projected to decline. However, due to the significant increase in extreme heat-associated deaths, the overall number of temperature-related deaths is projected to more than double under the lower-emissions scenario and more than triple under the higher-emissions scenario.

Although some people have suggested that rising temperatures may be beneficial in reducing cold-related health issues, our analysis suggests that the rise in extreme heat-related deaths will outweigh the decline in extreme cold-related deaths.

Can you explain how extreme temperatures result in deaths, particularly extreme heat?

Khatana: Extreme heat exposure can impact the body in numerous ways, exacerbating pre-existing cardiovascular, respiratory, or kidney conditions, among others. For example, extreme heat causes the heart to work harder to expel heat from the body. It can also lead to increased inflammation. For someone with pre-existing heart disease, this can cause complications like heart attacks or heart failure, which, in some cases, may lead to death. In cases of prolonged heat exposure, people can develop heat stroke, a dangerous medical condition that can lead to multi-organ failure and death.

What are the two emissions scenarios you looked at?

Khatana: We used two emissions scenarios commonly applied in climate models [from scientists of the Intergovernmental Panel on Climate Change]. SSP2-4.5 is the lower-emissions increase scenario, which models how greenhouse gas emissions may change in a world where many of the currently proposed emissions control policies are successfully implemented. SSP5-8.5 is the higher-emissions increase scenario, modeling how emissions may change in a society that continues to rely heavily on fossil fuels.

Are there differences in mortality by race and ethnicity?

Khatana: Although most groups and locations are projected to experience an increase in extreme temperature-associated mortality, Hispanic and Black adults are projected to see a greater increase compared to non-Hispanic white adults. This is likely due to differences in population growth rates and geographic distribution. We found that people living in metropolitan areas, which tend to have a higher proportion of racial and ethnic minorities, also had a greater projected increase. Additionally, our previous studies have shown that non-Hispanic Black adults currently experience a greater increase in mortality related to heat exposure. This may partly be due to the fact that neighborhoods with higher proportions of minority residents often have lower tree cover and less access to air conditioning, making the experienced temperature higher.

What are you thinking about next?

Khatana: I believe it’s crucial for future studies to explore measures that can mitigate the impact of extreme temperatures on public health. Some research suggests that increasing urban tree cover is associated with a reduction in heat-related deaths. Furthermore, our study shows that while temperature-related deaths are projected to increase under both emissions scenarios, the lower-emissions scenario is associated with fewer deaths. This underscores the urgent need for rapid reductions in greenhouse gas emissions.

---

The study, “Projections of Extreme Temperature-Related Deaths in the U.S.,” was published on September 20, 2024 in JAMA Network Open. Authors include Sameed Ahmed M. Khatana, Jonathan J. Szeto, Lauren A. Eberly, Ashwin S. Nathan, Jagadeesh Puvvula, and Aimin Chen.

---

Author

---