Extreme temperatures associated with heat waves can make everyone uncomfortable. When combined with conditions such as high humidity, sun exposure, stagnant air, and poor air quality, high temperatures can also become a health concern.
Some groups face a greater risk of heat-related illness than others. For instance, outdoor workers and athletes are at greater risk than office workers because they have increased exposure to heat. Other groups may be more vulnerable to the effects of high heat as a result of age or poor health, or the lack of resources that enable them to adapt or recover. Identifying specific factors that increase risk for some populations gives us a way to reduce exposure and vulnerability through adaptive actions. In some cases, simply increasing awareness of the risks that extreme heat poses to health can encourage people to take adaptive actions, such as going indoors or getting to a cooling center.
Experts in climate and health have developed the conceptual diagram at right to illustrate the exposure pathways by which climate change can affect human health. The diagram accounts for factors that positively or negatively influence health outcomes (gray side boxes): key factors that influence vulnerability for individuals (right box), and key factors that influence vulnerability at larger scales, such as natural and built environments and their management (left box). All these factors can affect an individual’s or a community’s vulnerability to extreme heat through changes in exposure, sensitivity, and adaptive capacity. The entire system may also be affected by climate change.
Children are at greater risk of heat-related health issues.
For vehicles parked in the sun for an hour, the average cabin temperature hit 116°F in one hour. For vehicles parked in the shade, average cabin temperature is still hot—about the same as the outside temperature—but significantly lower than those parked in the sun.
As dependents, children rely on others to keep them safe, and some may not have the resources or knowledge to protect themselves from extreme heat.
Children spend a good portion of their time in schools or day care settings, some of which may lack air conditioning.
Children are less efficient thermoregulators than adults; they have a smaller cardiovascular output and a higher metabolic rate than adults, which can increase vulnerability. Additionally, children often play outside in structured and unstructured activities. This exposes them to some of the same risks as outdoor workers and athletes experience (see below).
The Centers for Disease Control and Prevention (CDC) provides information to understand why children are vulnerable, where children are experiencing adverse health outcomes as a result of extreme heat (National Environmental Public Health Tracking Network), and how to reduce their risk (Extreme Heat Prevention Guide). These tools describe health outcomes of children in every state over many years, facilitating comparisons and further analysis.
Athletes are at risk of heat illness due to the combination of exposure, exertion, and, in some cases, wearing protective gear that traps heat. Outdoor activity exposes athletes to high temperatures, and conditions can be exacerbated by direct sunlight and/or poor air quality. Decision makers can use common tools to check current and future forecast air temperatures (NWS Graphical Forecasts), solar exposure (the opposite of cloud cover), and air quality (AirNow Air Quality Forecast), and factor those conditions into decisions about where and when to conduct practices and competitions.
Athletes are expected to push themselves physically, so the line between what is acceptable exertion and dangerous exertion may be blurred.
As athletes are expected to push themselves physically, the line between acceptable levels of exertion and dangerous levels of exertion during heat may be blurred. CDC's guide on Recognizing, Preventing, and Treating Heat-Related Illness can be useful in protecting athletes from heat.
A range of organizations offer information about the risk heat poses to athletes. While many athletes have suffered from complications due to overheating, the death of Korey Stringer, who was participating in a National Football League training camp in 2001 when he suffered heat stroke, led to the creation of an eponymous institute at the University of Connecticut for the prevention of such deaths in the future. This is one organization that conducts research and issues guidance for the prevention of heat-related morbidity and mortality in athletes.
For older adults, health complications such as cardiovascular issues can exacerbate the effects of extreme heat. Adults who require life-sustaining devices may be vulnerable during power outages that commonly accompany extreme heat events. Additionally, those who need constant access to oxygen, prescription drugs, or other consumable medical resources may not feel comfortable leaving their homes during a heat wave. Some older adults may also be using prescription drugs that affect their capability to thermoregulate or that block nerve impulses, both of which increase vulnerability to thermal extremes. The CDC offers information to help you recognize the signs of heat-related distress in older adults, and find tips you can offer to help them keep cool.
Older adults are also more likely to be socially isolated than some groups, as they are less likely to have occupations and may lack other community involvements. Empirical studies have documented the increased risk of morbidity and mortality due to extreme heat among older people. Older populations may be concentrated in retirement communities in states such as Florida or Colorado (where the Colorado Climate Change Vulnerability Study predicts a 125 percent increase in such populations by 2030). Such dense clusters of older residents may put extra pressure on early responders and heath care facilities during extreme heat in these areas. Finally, urban settings, with high rise structures and the urban heat island effect, may increase the risk of heat illness substantially, yet rural settings have factors such as social isolation and lack of transport or services which can also increase risk.
The first step in addressing the risk of heat illness among older adults is understanding where they live. The U.S. Environmental Protection Agency’s EJSCREEN tool helps decision makers examine demographic variables that may influence environmental health outcomes. For example, users can produce maps showing “percent of population over age 64." Additionally, the U.S. Department of Health and Human Services' emPOWER Map can show where Medicare beneficiaries or those who rely upon electricity-dependent medical and assistive equipment reside. Older residents may also be less likely to have or use air conditioners because of the expense of electricity. The HHS Low Income Home Energy Assistance Program (LIHEAP) can assist with this issue.
For pregnant women, extreme heat can be quite uncomfortable. Discomfort occurs not only because pregnant women tend to experience a general increase in their core body temperature regardless of the air temperature, but also because extreme heat events can increase the likelihood of common challenges during pregnancy, such as excessive sweating and heat rash. Importantly, extreme heat also poses health risk for a pregnant woman and her developing fetus. There is increasing evidence that extreme heat can increase the risk for preterm birth, low birth weight, fetal death, and infant mortality.,
There are numerous behaviors a pregnant woman can change to stay hydrated, cool, and reduce heat exposure. For example, pregnant women should drink water, reduce caffeine consumption, wear loose clothing, stay indoors during the hottest part of the day, and stay aware of heat warnings and advisories to reduce exposure. Although not a concern for all pregnant women, the National Institute for Occupational Safety and Health offers suggestions for reducing heat exposure in one’s work environment.
Emergency responders put themselves in danger repeatedly in the line of duty, and heat waves are no exception. Police officers, firefighters, paramedics, and the many others who protect people during heat waves need information to understand how to find and help those who are most vulnerable, while ensuring they are protected themselves. In order to support this population, the Federal Emergency Management Agency (FEMA) U.S. Fire Administration and the International Association of Fire Fighters (IAFF) developed the Emergency Incident Rehabilitation (PDF) report to inform decision makers of heat exposures that firefighters and other emergency responders face. The IAFF also hosts the Emergency Incident Rehabilitation Program, which contains training resources and other information.
Before an extreme heat event, emergency responders must prepare themselves to tend to members of vulnerable populations. The CDC tool Assessing Health Vulnerability to Climate Change: A Guide for Health Departments guides health departments in assessing local vulnerabilities to the health hazards associated with climate change. It's also important to assure the continuity of operations of vital health care resources during extreme heat events. The Sustainable and Climate-Resilient Health Care Facilities Toolkit provides information to build resilience of health care organizations.
When planning for extreme weather events that could knock out power and/or reduce transportation options, the emPOWER Map can be used to understand where Medicare beneficiaries or those who rely upon electricity-dependent medical and assistive equipment reside. People with mental illness (including older adults and those taking prescription medications that impair the body's ability to regulate temperature) can also be at increased risk of disease and death in extreme heat: the Substance Abuse and Mental Health Services Administration provides helpful information for serving these populations. Finally, a range of forecasting tools can keep you apprised of upcoming heat events on many time scales.
People who work outdoors—in agriculture, fishing, construction, or other service areas—or in situations where they don't have access to air conditioning are at risk for heat-related illnesses and injuries. These workers may have job tasks requiring great physical exertion, and the use of personal protective clothing and equipment may trap heat and prevent cooling. Many of these workers, particularly farm workers, may not have easy and quick access to water and shade. Lack of acclimatization in new workers and during heat waves also puts workers at higher risk. Some outdoor workers may also suffer from increased temperatures in cities due to the urban heat island effect, which can increase temperatures by 18 to 27°F (10 to 15°C) during the day, and 9 to 18°F (5 to 10°C) at night in urban areas compared to rural areas.
Learn more about heat health for outdoor workers in a story map created by the NIHHIS team. Story maps are web applications that combine maps, images, multimedia content, and narrative text. Open the story map "Protecting Outdoor Workers from Heat Illness" in a new tab/window.
The Occupational Safety and Health Administration (OSHA) issued a Heat Illness Prevention Training Guide and a Heat Safety Tool app for informing and protecting the occupational health of all workers. These resources can be found, along with other information, on the Campaign to Prevent Heat Illness in Outdoor Workers webpage. In addition, the National Institute for Occupational Safety and Health (NIOSH) offers the guidance document, Criteria for a Recommended Standard: Occupational Exposure to Heat and Hot Environments for employers and safety and health professionals, as well as other heat-related educational materials for workers. The Heat Stress Toolkit includes fact sheets, brochures, infographics, and more detailed information sheets. For outdoor workers in California, the report Preparing California for Extreme Heat: Guidance and Recommendations (PDF) has suggestions on mitigating heat risk for California’s agricultural and other outdoor workers. Finally, wildland firefighters experience atmospheric heat extremes as well as extreme heat from wildfires. The U.S. Forest Service's Fire and Aviation Management program provides information dealing with Heat Stress for Wildland Firefighters.
Military personnel can also be considered outdoor workers, and the Ready Campaign | Military Family Preparedness tool features information from the Navy, Army, Marine Corps, Air Force, and Coast Guard on how military families (and others) can prepare for extreme events. Additionally, the Air Force has a mobile app for Android and iPhones that can serve as a resource even when the internet is not accessible.
Pet owners should take special precautions to safeguard the health of their pets during extreme heat.
Pet owners should take special precautions to safeguard the health of their pets during extreme heat. All animals have different thermoneutral zones (TNZs)—ranges of temperatures within which their bodies needn’t work to stay warm (for example, by shivering) or cool (for example, by sweating or panting). In some cases, the TNZs may be somewhat close to humans’ (domestic dogs), while in other cases the TNZs may be skewed higher (domestic cats) or lower. Small animals, such as rodents, may be at increased risk for the same reason as children—their metabolic rate is much higher than larger animals due to their small size. Additionally, some of the same characteristics that make some humans more vulnerable than others are also in play with other animals, such as older or very young pets and pets with existing health conditions. Watch for warning signs, such as heavy panting or glazed eyes, because animals cannot tell you when they are too hot. Another risk to pets and service animals is the potential for burns to their paws and pads as paved surfaces may become excessively hot during a heat wave. Both the Best Friends Animal Society and the Humane Society provide excellent reference materials for understanding the risk of heat and warning signs for pets, as well as tips for mitigating heat risk, for instance, by making peanut butter popsicles or "keep cool" mats.
An additional factor to consider regarding pet ownership is that having a pet may influence the behavior of people in maladaptive ways during heat waves. For example, reluctance to leave a pet behind while seeking medical care for oneself or uncertainty as to whether a pet will be accepted at a cooling center could cause pet owners to remain in a hot building when it is unsafe. As a precaution, consider calling cooling centers well in advance of heat waves or heat season to determine if those nearest you will accept pets.
Additional information on populations of concern during heat waves is available in the Climate and Health Assessment. Additional tools, case studies, reports, and trainings are also available on NIHHIS to support extreme heat preparedness and resilience.