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What is Extreme Heat?

Extreme heat is the stealth killer. Its effects can catch you off guard and become life threatening quickly. Currently, the World Health Organization tells us that heat waves are considered among the most dangerous of natural hazards but rarely receive adequate attention because their death tolls and destruction are not always obvious. From 1998 to 2017, more than 166,000 people around the world died because of heat waves.

What we fear: We all remember those summer heat waves where it was so hot “you could fry an egg on the pavement.” But the thought of being in an extended heat wave with daytime temperatures at or above 125 degrees is beyond imagining, especially if there are no means by which we can escape the heat. The human body can only accommodate temperatures above 95 degrees with high humidity for short periods of time and being caught in a heat wave with no respite can be frightening as the signals for threats to health are difficult to sense in time to get help.

What we experience: We pay close attention to the thermometer and what the weather forecast terms the Heat Index. The Heat Index is a measure of how hot it really feels when relative humidity is factored in with the actual air temperature. When the Heat Index reaches into the 90s and beyond, we try to find ways to manage our exposure to the heat, if we have the means to do so. 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 become a major health concern. Some groups face a greater risk of heat-related illness than others. People without access to air conditioning or other means of cooling down and those who have underlying health conditions are particularly vulnerable when the temperature soars.

Learn more about our work to support Client Resilient Health Clinics.

For decades at Americares, we have seen up close the staggering magnitude of extreme weather losses for families and communities – the personal history and common goods. Access to medicine security and to health services become early casualties. We know that immediate access to primary health services, including mental health support, along with medicines and medical supplies will save lives and restore health. No matter where extreme weather disasters strike, we are there, and together with our partners, even in the worst times, we can make health happen.

Learn more about health crises from Climate Change: Hurricanes. Floods. Wildfires.

What Regions Face the Greatest Threats from Extreme Heat Events?

Areas at Risk

While extreme heat events can occur anywhere in the world, some regions are more vulnerable due to a combination of factors like climate, population vulnerability, and limited resources.

Less-developed countries with hot climates: Countries like Afghanistan, Chad, Guatemala, Honduras and Nicaragua are particularly susceptible. These countries are in regions that already experience scorching temperatures, and climate change is making it worse. They may also lack resources such as widespread air conditioning or robust healthcare systems to prepare for and respond to extreme heat events. The latest heat emergency has occurred in South Sudan a country already grappling with the extremes of climate change with recurring droughts and floods. Temperatures approached 113 degrees Fahrenheit far above the usual 90-degree range during the normal dry season.

Densely populated areas: Heat waves can be particularly dangerous in densely populated areas, due to the urban heat island effect. This phenomenon occurs when buildings and pavement trap heat, making temperatures even higher than surrounding areas. Cities in both developed and developing countries can be at risk, such as Beijing and Shanghai (China), and Delhi (India). Parts of northern and central India recorded their highest average temperatures for April 2022 and the cycle repeated in 2023. Delhi recorded a temperature of 116°F. These record temperatures are especially deadly for socially vulnerable and disadvantaged communities.

In the United States: Southern states in the U.S. naturally experience hotter temperatures. States like Texas, Arizona, Nevada, California, and much of the Southwest are more likely to see scorching heat waves. The demands on an already over-burdened infrastructure and dwindling water supplies can also contribute to heat emergencies in these states. Densely populated cities like Phoenix, Houston, and Miami are particularly vulnerable as they experience the urban island heat effect. People in rural areas may lack access to air conditioning or cooling centers, making them susceptible during heat waves. Additionally, limited healthcare access and emergency medical services in some rural regions can complicate response efforts. Disadvantaged communities often have poorer quality housing with inadequate insulation or ventilation, and they may also be less likely to have air conditioning. Visit for the latest extreme heat forecast.

In Europe: Southern European countries such as Italy and even further north in the United Kingdom are facing the effects of climate change such as a shifting jet stream, melting Artic ice and reduced snow cover which are contributing factors in rising temperature on the continent. Countries that have not historically faced such extreme heat conditions often have limited experience in managing a heat emergency and lack significant availability of air conditioning.

How Do We Predict Extreme Heat Emergencies?

The Signs

Climate change has become a major factor driving the rise in global temperatures and the extreme heat events that are becoming more common and deadly each year.

The National Weather Service uses a couple of tools to measure the danger from rising temperatures and to issue extreme heat warnings:

The Heat Index is a measure of how hot it really feels when relative humidity is factored in with the actual air temperature. You will hear your weather forecaster refer to this measure frequently as they might say that with the temperature at 90 degrees, it feels like 117 degrees (the Heat Index number) if the humidity is 85 percent. The National Weather Service will initiate alert procedures when the Heat Index is expected to exceed 105°-110°F (depending on local climate) for at least 2 consecutive days. This chart from the National Weather Service shows how the Heat Index is calculated.

In addition, exposure to full sunshine can increase heat index values by up to 15°F. Also, strong winds, particularly with very hot, dry air, can be extremely hazardous. And why is the Heat Index number so significant? It directly relates to how the body cools itself through sweat which evaporates, taking some of the heat with it. But when the air is extremely humid, sweat evaporates more slowly, keeping the human body from cooling itself.

Wet Bulb Globe Temperature (WBGT) uses temperature, relative humidity, wind, solar radiation, and other weather parameters to assess heat risks on humans. It’s a particularly effective indicator of heat stress for active populations such as outdoor workers and athletes.

Heat Risk measures the level of heat danger in a particular area, along with identifying groups potentially most at risk at that level. The National Weather Service. Several criteria are considered:

  • How significantly above normal the temperatures are
  • The time of the year 
  • Duration of unusual heat
  • If those temperatures are at levels that pose an elevated risk for heat complications
  • How unusually warm the overnight temperatures are

How large the difference is between overnight lows and daytime high temperatures

For more information on measuring extreme heat risks visit the National Weather Service.

What are the Health Threats from Extreme Heat?

The Dangers

Global temperatures and the frequency and intensity of heatwaves will rise in the 21st century as a result of climate change.

Extended periods of high day and nighttime temperatures create cumulative physiological stress on the human body which adds to the top causes of death globally, including respiratory and cardiovascular diseases, diabetes and kidney disease. Extreme heat is the biggest threat to the most vulnerable population, especially the elderly, young children and people in disadvantaged communities.

When the Heat Index exceeds 105, extreme heat warnings begin to appear. The response of the body to extreme heat manifests itself in very specific ways that can easily be overlooked before heat stroke. Heat stroke is the most serious heat-related illness and requires immediate medical attention. It occurs when the body is unable to control its temperature. There are three stages of heat-related illness that end in heat stroke:

  • Heat cramps: These are painful muscle cramps and spasms that usually occur in the legs and abdomen. They are caused by dehydration and electrolyte imbalance – a warning to drink more water and add electrolytes.
  • Heat exhaustion: This is a more serious condition that occurs when the body is losing fluids and electrolytes faster than they can be replaced. Symptoms of heat exhaustion include heavy sweating, headache, dizziness, nausea, vomiting, fatigue, and weak pulse.
  • Heat stroke: This is a medical emergency. The body is unable to regulate its temperature. Symptoms of heat stroke include a body temperature of 103°F (39.4°C) or higher, hot, red, dry or damp skin, confusion, agitation, nausea, vomiting, headache, rapid and strong pulse, fainting, and loss of consciousness.

Americares Responding to and Preparing for Extreme Heat Emergencies

Our Work

Get Ready for Extreme Heat

Recognizing that rising temperatures from Climate Change are increasing health risks to vulnerable populations around the world, Americares is working with our health care partners in clinics to prepare communities to meet the threat from extreme heat events and to provide life saving health services to those people most affected by heat emergencies.

In the United States, we are working with Free Clinics to make them more Climate Resilient by providing resources for clinic staff and patients in the event of Extreme Heat emergencies.

Our Climate Health Equity for Community Clinics Program at health clinics in Arizona, Florida and Louisiana is designed to protect the most vulnerable patients from the health impacts of climate change, including extreme heat. Watch the video to see how we are confronting this health crisis from Climate Change.

It is crucial for everyone to be prepared
for an Extreme Heat emergency.

As we get ready for the next Extreme Heat emergency, we know that we can’t do it without you.

Please help your neighbors near and far with a gift right now.

Our Work:
Responding to Extreme Weather and Other Disasters