Heat should not be underestimated. Unlike hurricanes or floods, which are more visually dramatic, heat is a leading cause of weather-related fatalities in the U.S. Globally, a recent report indicates that extreme heat causes one death every minute, with this rate having increased by 23 percent since the 1990s.
Heat-related fatalities are often underreported both in the U.S. and internationally. Those most at risk include outdoor workers, the elderly, children, and individuals with chronic health issues. However, heat can pose a threat to anyone, especially as societal biases often regard sunny days as ideal weather, which can lead to underestimating the associated dangers.
Grist has been documenting the growing threat of extreme heat for several years. As we face ongoing years of record-high temperatures, we are compiling this coverage to emphasize the importance of taking heat seriously and how to protect oneself.
The rising threat of heat
Simply put, warm regions are experiencing even higher temperatures, and areas previously unaffected by extreme heat are increasingly vulnerable to dangerous conditions.
The risk of heat is increasing. Individual heat events cannot be directly linked to climate change, but the trend of more frequent and intense heat waves aligns with climate change impacts. Scientific agreement now indicates that climate change has influenced the likelihood and severity of nearly all heat waves.
Even during years with harsh cold spells, the average global temperature continues to rise.
Natural phenomena like the El Niño weather pattern can intensify the warming effects of climate change. During an El Niño year, elevated Pacific Ocean temperatures typically lead to increased global heat, with the hottest years often recorded during these periods.
The term “heat wave” generally refers to any spell of unusually hot weather. One of the most severe forms of heat waves is caused by a “heat dome,” where a high-pressure system traps warm air in a region, intensifying heat and humidity as it lingers.
Humidity makes heat even more dangerous. Any type of heat can be hazardous when your body can’t sweat quickly enough to stay cool. Heat and humidity together make it difficult for sweat to evaporate, which hinders the body’s natural cooling process.
This is why you might hear about “wet bulb temperature,” a measurement that accounts for both heat and humidity — essentially the temperature we feel after sweat has cooled us down.
When the wet bulb temperature exceeds 95 degrees Fahrenheit, the human body loses its ability to cool down, a threshold already surpassed more than a dozen times, mainly in Pakistan and the Arabian Peninsula. Even at a wet bulb temperature as low as 86 degrees Fahrenheit, healthy young adults may experience adverse health effects.
Heat affects your whole body
Exposure to high heat has immediate health effects. Extreme heat causes the heart to pump two to four times more blood per minute to cool the body. This can lead to dehydration, making blood thicker and harder to circulate, potentially resulting in heat exhaustion, heatstroke, or even heart failure. On very hot days, the risk of burns from hot surfaces like pavement is also present.
Every year, hundreds of thousands of people in the U.S. visit emergency departments due to heat-related illnesses and associated cardiovascular, respiratory, and kidney problems.
What to watch for: The first sign of severe dehydration is often cramps, which might resemble normal exercise cramps.
Symptoms of heat exhaustion include muscle aches or cramps, headache, excessive sweating and thirst, dizziness, nausea or vomiting, and pale, cool, clammy skin, especially on the extremities.
To treat heat exhaustion, lower the person’s body temperature by removing heavy clothing, providing water, and moving them to a shaded area or air-conditioned space. Laying them down with elevated legs and using damp cloths or misting with water can also help cool the body.
Heatstroke occurs when the body can no longer regulate its temperature, reaching dangerous internal levels that can lead to permanent brain damage or death. Look for symptoms such as confusion, irritability, unresponsiveness, severe fatigue, rapid pulse, nausea, vomiting, diarrhea, lack of sweat (though sweating can still occur), and hot, dry skin.
If heatstroke is suspected, call 911 and immediately immerse the individual in cold or iced water, or apply ice to areas near large blood vessels like the groin, armpits, neck, and core.
Heat’s health effects also reach much deeper. Exposure to extreme heat affects us in various ways that are only beginning to be understood by doctors and scientists. For instance, heat has been shown to increase violent crime rates and is linked to worsening mental health issues, including suicide.
Prolonged exposure to heat can lead to chronic health problems like cardiovascular disease. In some of the world’s hottest regions, outdoor workers are developing a rare form of chronic kidney disease associated with long-term dehydration and heat stress.
Nighttime heat is a particular driver. Nighttime temperatures are increasing faster than daytime temperatures in much of the world, eliminating a crucial window for cooling down.
We also sleep worse when it’s hot, already losing 45 hours of sleep per year due to the heat.
Ways to prepare
Your house makes a big difference. If a heat wave is headed your way, dehumidify your house to get the indoor humidity down. Seal off openings around windows and doors to prevent hot air from entering. Cover windows to prevent the sun from heating up the indoors — blackout shades, blinds, or even DIY solutions work.
In a low humidity environment, you can even DIY your own air conditioning.
Keep water, electrolytes, and ice on hand, at home and at work, and identify cool places to go, like a public library. This isn’t just useful to ease boredom — heat can place additional strain on the electricity grid as everyone runs their air conditioners, sometimes resulting in power outages.
In the long term: Retrofits like reflective roofs, window overhangs to block the sun, and better insulation can provide more relief.
And as you’re preparing, don’t forget to check on vulnerable neighbors and community members.
Grist has even more advice for safety and preparedness. Go deeper on community readiness and workplace safety here: Extreme heat 101
And more tips on emergency preparedness, including for heat and power outages, can be found here: How to prepare for a disaster
Stay safe out there (or, better yet, inside where it’s cool).
