Climate Adaptation to Health Risks of Extreme Heat

Periods of extreme heat, such as the recent summer heat dome covering much of the United States, pose serious health risks. Extreme heat can exacerbate chronic health conditions such as heart disease, respiratory and mental health conditions (1). Vulnerable populations are at increased risk, particularly those that are elderly or very young, as well the unhoused population (2).  

Climate change is likely causing these events to occur more often and heat to become more extreme. Models project that by 2099 heat wave temperatures will increase by 3.4 to 6.6 degrees Celsius and with longer duration (3).  By the end of this century, heat waves will not only increase in temperature and severity but will also occur more frequently. Extreme heat waves, such as in Russia in the summer of 2010, which lasted from June to mid-August and led to 55,000 deaths, could start occurring as often as every 2 years in regions including in Europe and North America (4). Scientists project that, by the late twenty-first century (2070-2099), three to four heat waves will per summer will occur on average (5). Severe heat poses an increasing threat to public health as well as a challenge for our health systems in responding to these events to prevent morbidity and mortality.

Extreme heat is defined based on what is normal for a geographical region and the combination of high heat and humidity (6).  For example, extreme heat defined as 92 degrees in Boston may need to reach over 100 degrees in Phoenix to be considered extreme (6).  The heat index uses air temperature and relative humidity to provide an apparent temperature on the human body and provides the likelihood of heat disorders with prolonged exposure to heat.  The HeatRisk Forecast Tool, developed by the CDC and NOAA, provides guidance on the risk of heat-related health impacts and daily dynamic temperature threshold guidance (7).

Extreme heat increases the need for urgent medical care, particularly among those at increased risk of heat-related illness, including children, elderly, workers and those with chronic medical conditions. ER utilization data can help identify those at increased risk. Past data trends support a direct correlation between increased heat and ER utilization and 911 calls for heat related health conditions, with heat-related ER visits increasing by roughly 70 percent during periods of extreme heat (8). However, barriers to accessing the ER can also result in under-reporting of heat-related illness in at-risk populations (9).  Older adults are particularly at risk of heat related illness due to a decreased ability to thermoregulate, comorbidities, medication use, and sensory or physical impairments that may isolate them or make it difficult to leave their home (2, 10). The combination of an aging global population and increasing temperatures is projected to accelerate chronic and acute heat exposure for older adults, placing an increased demand on public health and health systems (10).

As these trends increase with climate change, we risk straining our emergency response infrastructure and hospitals systems.  Public health systems attempt to mitigate the risk by issuing heat alerts, opening cooling centers, and providing health education on symptoms of heat exposure.  These efforts help prevent heat related morbidity, however a greater focus on upstream prevention is needed for climate adaptation.  Models such as CDC's BRACE Framework (Building Resilience Against Climate Effects) (11), and collaboratives such as the Global Heat Health Information Network (12), can mitigate heat-related risk through building a systemic response.

Physicians can make an impact by educating their patients on health risks of extreme heat and ensuring their patients have an individual action plan and access to available community resources in the event of extreme heat. Tools such as the CDC's Heat & Health Tracker can help identify if their community and patients are at risk of health effects from extreme heat (13).

Successful climate adaptation to extreme heat should include systems that address risk in vulnerable populations and regional variation, while remaining integrated at the state and national level to optimize communication and coordinated response plans.  Access to real-time data identifying heat-related health risk can help physicians and public health organizations prevent unnecessary heat-related deaths. Additionally, collection of data should be a priority to protect not only vulnerable populations but the ability of our health and hospital systems to respond to extreme heat events.

References:  

1. https://www.who.int/news-room/fact-sheets/detail/climate-change-heat-and-health    
2. https://www.heat.gov/pages/who-is-at-risk-to-extreme-heat
3. Brown, Simon J. "Future changes in heatwave severity, duration and frequency due to climate change for the most populous cities." Weather and Climate Extremes 30 (2020): 100278
4. Russo, Simone, et al. "Magnitude of extreme heat waves in present climate and their projection in a warming world." Journal of Geophysical Research: Atmospheres 119.22 (2014): 12-500.
5. Lhotka, Ondřej, Jan Kyselý, and Aleš Farda. "Climate change scenarios of heat waves in Central Europe and their uncertainties." Theoretical and applied climatology 131.3(2018): 1043-1054.
6. https://www.epa.gov/sites/default/files/2016-10/documents/extreme-heat-guidebook.pdf
7. https://www.wpc.ncep.noaa.gov/heatrisk/
8. Dring P, Armstrong M, Alexander R, Xiang H. Emergency Department Visits for Heat-Related Emergency Conditions in the United States from 2008-2020. Int J Environ Res Public Health. 2022 Nov 10;19(22):14781. doi: 10.3390/ijerph192214781. PMID: 36429500; PMCID: PMC9690248
9. Sahar Derakhshan, David P. Eisenman, Rupa Basu, Travis Longcore, Do social vulnerability indices correlate with extreme heat health outcomes?The Journal of Climate Change and Health, Volume 18, 2024,100276, ISSN 2667-2782, https://doi.org/10.1016/j.joclim.2023.100276.
10. Falchetta, G., De Cian, E., Sue Wing, I. et al. Global projections of heat exposure of older adults. Nat Commun 15, 3678 (2024). https://doi.org/10.1038/s41467-024-47197-5
11. https://www.cdc.gov/climate-health/php/brace/index.html
12. https://ghhin.org/about-us/
13. https://ephtracking.cdc.gov/Applications/heatTracker/