NAMClimate Health Hazard SummarySummary: Health Impacts of Extreme Heat

Extreme Heat as a Climate Health Hazard

This summary is part of the NAM’s “Communicating About Climate Change and Health” project. The project aims to support health providers and other communicators in sharing actionable information with patients and the public.

Health Impacts of Extreme Heat

Climate change has directly contributed to rising temperatures around the world. The global mean temperature has increased by 2 degrees Fahrenheit (1 degree Celsius) since preindustrial times, and heatwaves are becoming more frequent, longer, and more intense.

Exposure to extreme heat can have a range of outcomes for health, including:

Mild effects include conditions like heat rash, which occurs when sweat ducts are blocked, or muscle cramps caused by loss of electrolytes through excessive sweating.
Moderate effects include exhaustion, lack of energy, headache, and dizziness.
Severe effects include heatstroke, a condition that occurs when the body can no longer cool itself down. If untreated, heat stroke can lead to organ damage and death.

Extreme heat is often fatal. In 2023, 2,325 people died from heat in the United States. Heat-related deaths in people older than age 65 have increased by 68% over the past two decades. One study across 43 countries estimated that 37% of heat-related deaths are attributable to human-induced climate change.

In addition to direct and immediate effects, exposure to high temperatures can contribute to adverse birth outcomes and exacerbate conditions like heart disease, ischemic stroke, asthma, respiratory infections and diseases, and kidney failure.

Extreme heat can also contribute to spikes in violence and aggravate symptoms of mental health disorders. Research has also shown that emergency room visits for mental health reasons increase during heat waves. Given the increasing frequency and severity of heatwaves, it is important for people to know how to protect their health.

Case Example

2021 Heatwave in the Pacific Northwest

In June 2021, the Pacific Northwest region of the United States and Canada experienced a wave of record-breaking high temperatures. Temperatures soared as high as 108 degrees Fahrenheit between June 27 and June 29.

People in the region were severely impacted, given that many households lacked air conditioning. Based on a report from the Centers for Disease Control and Prevention, emergency room visits due to heat illness in the region were 69 times higher than in previous years. Across Washington, Oregon, and Alaska, there were 1,090 heat-related emergency room visits on June 28. The 2021 heat wave contributed to an estimated 196 heat-related deaths in the state of Washington, 100 in Oregon, and 619 in British Columbia, Canada.

Local preparedness for this extreme event was inadequate, and the health consequences were significant. As heat emergencies become more frequent, it is critical that communities put preparedness resources in place, particularly strategies to protect the most vulnerable--including children, older adults, outdoor workers, people experiencing homelessness, people with chronic conditions, and people with mental health disorders.

Steps to Protect Your Health

Your risk of heat related illness depends on individual factors (age, health conditions, pregnancy status, etc.), your exposure to heat, and sociocultural factors including housing status, access to health care, and occupation. Outdoor workers (e.g., construction, landscaping, farming, transportation, and sanitation workers), older adults, infants and young children, athletes, pregnant women, and people with mental illness are more susceptible to heat impacts.

Certain medications and substances can increase your risk of heat-related illness, including alcohol, amphetamines, antihistamines, antipsychotics, anticholinergics, benzodiazepines, beta-blockers, diuretics, and others. In addition, heat exposure affects the stability of certain medications (e.g., insulin, biologics, inhalers, and epipens) and the accuracy of certain point-of-care tests (e.g. glucose strips). Such medications and tests need to be kept at recommended temperatures during heatwaves. Discuss the proper handling of medications with a pharmacist or other health provider.

During an extreme heat event, it is important to recognize the signs of heatstroke to protect yourself and others. Someone experiencing heatstroke will be hot and dry to the touch or pale and sweating and confused. Lie the person down, elevate their legs, remove clothing, apply cooling materials, and seek help immediately. Treatment may involve rehydration, rapid cooling of the body temperature, and intervention to address any organ damage.

To help prevent heat-related illness, you can keep your living space cool with fans, air conditioning, and misting. If this is not sufficient, local jurisdictions often set up cooling centers in the community for residents. Try to limit excess physical activity, wear lightweight clothing, take cold showers, and stay hydrated.

Mitigation Strategies

At the individual level, people can take steps to better insulate their homes, block the sunlight from windows, and plant trees to create shade. As the community level, people can support policies and programming to mitigate the effects of heatwaves. In addition to cooling centers and warning systems to communicate during extreme heat events, cities and towns can help mitigate effects by planting trees along city streets, and building shade structures at parks and bus stops. Other interventions include urban gardens, rain gardens, green roofs, urban greening, and creation of water bodies. These strategies can not only reduce the urban heat island effect and improve local air quality, but also contribute to improved physical and mental health for residents.

Broadly speaking, large systemic action steps must be taken to prevent global temperatures from rising further. These include reducing carbon emissions across all sectors, building a more sustainable food system, creating infrastructure for reliable public transportation, phasing out reliance on coal and oil, and transitioning to renewable energy sources.

References and Related Resources

Heat Stroke (Cleveland Clinic, 2024)
The 2022 report of the Lancet Countdown on health and climate change: health at the mercy of fossil fuels (Romanello et al., 2022)
Trends of Heat-Related Deaths in the US, 1999-2023 (Howard et al., 2024)
Preventing Heat-Related Illness among Outdoor Workers — Opportunities for Clinicians and Policymakers (Sokas et al., 2023)
The burden of heat-related mortality attributable to recent human-induced climate change (Vicedo-Cabrera et al., 2021)
Treatment and Prevention of Heat-Related Illness (Sorensen and Hess, 2022)
Association between extreme temperatures and emergency room visits related to mental disorders: A multi-region time-series study in New York, USA (Yoo et al., 2021)
Rapid attribution analysis of the extraordinary heat wave on the Pacific coast of the US and Canada in June 2021 (Philip et al., 2022)
Heat Wave 2021 (Washington State Department of Health, 2021)
Introduction to JAMA Climate Change and Health Series (Ebi and Hess, 2024)
Astounding heat obliterates all-time records across the Pacific Northwest and Western Canada in June 2021 (NOAA, 2021)
Preparing Vulnerable Populations for 2024 Heat Waves: A
Specialty-Based Approach (Medical Society Consortium on Climate & Health, 2024)
Prevent or Minimize Hazards from Extreme Heat Events (USDA, n.d.)
Climate Change Heat Adaptation Guide for Homeowners (ClimateCheck, n.d.)
Climate change and health: three grand challenges (Campbell-Lendrum et al., 2023)

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