Older adults and children have a higher risk of dying or becoming ill due to extreme heat [Very High Confidence]. People working outdoors, the socially isolated and economically disadvantaged, those with chronic illnesses, as well as some communities of color, are also especially vulnerable to death or illness [Very High Confidence].

This finding is from chapter 2 of The Impacts of Climate Change on Human Health in the United States: A Scientific Assessment.

Process for developing key messages: The chapter was developed through technical discussions of relevant evidence and expert deliberation by the report authors at several workshops, teleconferences, and email exchanges. The authors considered inputs and comments submitted by the public, the National Academies of Sciences, and Federal agencies. For additional information on the overall report process, see Appendices 2–3.

The content of this chapter was determined after reviewing the collected literature. The authors determined that there was substantial literature available to characterize both observed and projected mortality from elevated temperatures, with sufficient literature available to also characterize mortality from cold as well as cold-related hospitalizations and illness. Populations of concern were also considered to be a high priority for this chapter. As discussed in the chapter, there were limitations in terms of the state of the literature on understanding how future adaptation will influence climate-related changes in temperature-related mortality, addressing the impact of temperature on rural populations, and examining health-related endpoints other than mortality and morbidity.

Description of evidence base: The relationship between increased temperatures and deaths in elderly populations is well-understood. An increased risk of respiratory and cardiovascular death is observed in elderly populations during temperature extremes due to reduced thermoregulation.b9525432-c24b-4aee-9b0f-1783af53f48d,8bf8d41a-8b94-4ec2-95f0-cfd77b48685e,199eb13a-09ce-4af0-bc70-e26881a28c33,e2f39823-225f-43ea-ae65-dfc3d73bf9a6

Studies cite dehydration, electrolyte imbalance, fever, heat stress, hyperthermia, and renal disease as the primary health conditions in children exposed to heat waves. Causes of heat-related illness in children include inefficient thermoregulation, reduced cardiovascular output, and heightened metabolic rate. Children also spend a considerable amount of time outdoors and participating in vigorous activities.b9525432-c24b-4aee-9b0f-1783af53f48d,8bf8d41a-8b94-4ec2-95f0-cfd77b48685e,8e74af6d-bae1-4355-92b9-c186e2d09b8c,2a0a09ec-bc6f-4662-9894-ff2ea09c1f57 A limited number of studies found evidence of cold-related mortality in children; however, no study has examined the relationship between cold temperature and cause-specific mortality.8e74af6d-bae1-4355-92b9-c186e2d09b8c

Certain occupational groups that spend a great deal of time exposed to extreme temperatures, such as agricultural workers, construction workers, and electricity and pipeline utility workers, are at increased risk for heat- and cold-related illness, especially where jobs involve heavy exertion.de5b6f9d-388d-4f67-8115-ad5fca6a95d5,ec85e5b1-7c3e-48b7-9919-f04bdb7afce3,480e807c-24a2-43ab-9d53-6cff5cd095f2 Lack of heat-illness-prevention programs in the workplace that include provisions for acclimatization was found to be a factor strongly associated with extreme temperature-related death.ec85e5b1-7c3e-48b7-9919-f04bdb7afce3

Race, ethnicity, and socioeconomic status have been shown to impact vulnerability to temperature extremes. Several studies have identified non-Hispanic Black populations to be more vulnerable than other racial and ethnic groups for experiencing detrimental consequences of exposure to temperature extremes.b9525432-c24b-4aee-9b0f-1783af53f48d,8bf8d41a-8b94-4ec2-95f0-cfd77b48685e,199eb13a-09ce-4af0-bc70-e26881a28c33,2a0a09ec-bc6f-4662-9894-ff2ea09c1f57,2de8f6a6-933e-4bc7-8224-e754696e2a53 Studies suggest comorbidities that enhance susceptibility to higher temperatures, availability and use of air conditioning, disparities in heat risk-related land cover characteristics, and other environmental justice issues contribute to increased vulnerability of non-Hispanic Blacks.b9525432-c24b-4aee-9b0f-1783af53f48d,8bf8d41a-8b94-4ec2-95f0-cfd77b48685e,1aca1900-c64c-4624-a696-3aab59ba6673,2de8f6a6-933e-4bc7-8224-e754696e2a53,29da63ed-20d4-4ac6-9ec7-ac886a25c040

Dementia, mood disorders, neurosis and stress-related illnesses, and substance abuse are shown to be impacted by extreme heat.de5b6f9d-388d-4f67-8115-ad5fca6a95d5,922bcd50-dd07-4e05-afc7-fe3bcb1a953a,1e9a7907-02f2-4da8-9e93-131f92515dbc,2a9775ae-a280-4260-985f-0e66d0ef8c11 Some medications interfere with thermoregulation, increasing vulnerability to heat.1e9a7907-02f2-4da8-9e93-131f92515dbc

New information and remaining uncertainties: The literature available at the time of the development of the 2014 NCA had identified a number of vulnerable populations that were disproportionately at risk during heat waves, and literature since that time has only strengthened the understanding of the elevated risks for these populations. There continues to be a need for better understanding of the relative importance of genetics and environmental justice issues with regards to the observed higher risk for non-Hispanic Blacks, more work on understanding the risks to pregnant women from extreme temperature events, and a better understanding of the relationship between extreme cold vulnerabilities in populations of concern.

Assessment of confidence based on evidence: Although some details regarding causation and identifying the most vulnerable subpopulations still require research, there is a large body of literature that demonstrates the increased vulnerability to extreme heat of a number of groups, and therefore there is very high confidence that the listed populations of concern are at greater risk of temperature-related death and illness.

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