When you stop sweating, it starts. Sweat cools you typically down by releasing heat into the air as it evaporates. Still, if your body becomes dehydrated or the external mixture of hot air and humidity becomes too high, you won’t be able to push the salty liquid through your pores anymore. As blood rushes toward your skin, you flush all over in an attempt to transfer heat away from your core. As your salt reserves diminish, your muscles cramp. As your body mounts an immunological response, your organs enlarge. Your thoughts get hazy. You may start having hallucinations. You vomit so that your stomach doesn’t have to expend energy on digestion. Your heart skips a beat, and your brain throbs. You may start having seizures.
Death comes in the form of a heart attack or organ failure, whether it arrives within an hour or a few days. Your core temperature may rise to 105°F in the throes of heatstroke, yet if you’re alone—as many victims are—you’ll be freezing by the time help arrives. It’s unlikely that anyone will realize that heat was the actual killer.
When it becomes too hot, the human body begins to break down. Shane Campbell-Staton, an evolutionary scientist at Princeton University who studies the effects of severe temperatures on people and animals, says, “We have to maintain a very narrow range of body temperatures.” Most of us feel at ease when the temperature outside is between 68 and 77 degrees Fahrenheit, allowing us to keep our internal thermostat at roughly 98 degrees. When the environment pushes us past those boundaries, the delicate balance of chemical reactions that keep us alive begins to sway, resulting in a cascade of negative consequences that can be fatal.
Only approximately 700 people die in the United States each year due to high heat, primarily among vulnerable populations such as the homeless and elderly and persons who spend long periods outside for work or recreation. According to Scott Greene, a University of Oklahoma geographer who has been researching the subject since the 1990s, specialists who examine the links between weather and human health believe the actual number is significantly higher. Extreme highs may be to blame for thousands of deaths in the United States each year and many more around the world. Given that most of them go unreported, it’s difficult to say just how many there are. But, whatever the gloomy total, one thing is sure: there will be more in the years ahead.
Without immediate climate action, we will likely see a steep increase in extreme heat occurrences across the country by the middle of the century. That means a more significant proportion of the population will expose to dangerously high temperatures, which the National Weather Service defines as triple digits, or temperatures in the 90s with 65 percent humidity or more.
According to recent estimates from the Union of Concerned Scientists, by 2050, approximately 90 million people will have endured 30 days or more of 105°F temperatures, compared to fewer than 1 million in the late 1900s. The Sunbelt and the southern Great Plains will hardest hit by the 30 scorchers, which will strike roughly one-third of American cities. Temperatures in the Northeast might reach 90°F for up to 42 days a year, while comparable estimates expect hotter than 100 days in the Midwest. We can protect ourselves by adapting our lifestyles to these conditions. Still, public health experts say it will take a concerted effort from local, state, and national governments to educate people about the dangers of heat, alert them when temperatures rise too high and provide public air conditioning and water protection solutions.
Some of us are more prone to being exploited than others. Children sweat less and have higher surface-to-body-mass ratios, but the elderly do not sweat or pump blood as efficiently as children do. Antipsychotics and blood pressure medicines, for example, can cause internal thermometers to malfunction. People who don’t have a home or access to air conditioning don’t have a comfortable place to cool off, and construction workers and other laborers frequently work outside during the hottest parts of the day.
However, everyone might be affected by rising temperatures. Even temperatures in the 80s, according to the National Weather Service’s heat index, can cause disease if you expose for long periods when humidity is high or if you’re doing vigorous outdoor activities like athletics. The risk rises in lockstep with the amount of moisture in the air and the temperature.
However, it’s unclear how probable a person is to die as a result of exposure. That’s why Greene and others in his field look at how many individuals die in a specific location during an extremely hot period, rather than only looking at deaths coded as hyperthermia-related by coroners or medical examiners. They look for what is known as “excess deaths,” or deaths that are higher than the average for an area with similar demographics at that time of year. According to a similar study published in Environmental Epidemiology in 2020, heat is a direct or indirect cause of up to 10,000 deaths in the United States each year, significantly more than the official figure. The conditions are ideal for that number to continue to rise, but the crisis is already knocking on our door. According to official statistics, heat is already the greatest weather-related death in the country, ahead of winter storms, hurricanes, and flooding.
However, there is still time to avoid horrific deaths. When Greene began his studies in this sector in the 1990s, a period of dangerously hot weather in the United States—most famously, the 1995 Chicago heat wave, which killed over 700 people in five days—prompted towns around the country to begin preparing for the worst. According to the CDC, there hasn’t been enough research on such programs to identify the same advantages, but the evidence is encouraging. One of the most important developments to come out of those efforts is the widespread deployment of warning systems to make inhabitants aware of excessive temperatures and their health hazards. For example, a study of one such project in Philadelphia from 1995 to 1998 indicated that the city’s initiatives saved 117 lives over three years. According to Greene, the urban area’s response infrastructure also played a critical impact. They educated the public about extreme heat hazards, and local utilities continued to provide service even when payments were past due. Cooling centers provided shelter and water. The city expanded staffing for emergency medical services. Greene and others are still trying to figure out how much each of these mitigating actions has helped. Nonetheless, he believes that simply raising public awareness about the dangers might go a long way toward saving lives.
However, scorching spells that catch inhabitants off guard remain a worry, particularly in cities. The urban heat island effect can elevate temperatures by several degrees in regions with much heat-retaining concrete and a lack of trees compared to adjacent locations. As a result, densely populated metropolises may enter the danger zone while residents in the suburbs are unaffected.
Even while modern warning systems and infrastructure have aided the situation, more work is still to do. According to Princeton’s Campbell-Staton, “the major factor that separates us from the rest of the tree of life is our unique ability to buffer ourselves against extremes.”
According to Greene, city, county, state, and federal governments must coordinate their responses to keep the number of deaths low even as temperatures rise. He wants to see a more robust national forecasting effort to predict temperature spikes as far ahead as feasible. Cities might prepare with advance notice by releasing emergency money and adequately staffing infrastructures such as ambulances and cooling centers. Such warnings could also explicitly state what severe heat means in a specific location: Due to baseline preparedness and local knowledge, an inch of snow in Atlanta is more of an emergency than in Boston. Therefore you might not need a heat warning in Phoenix for the same temperatures as in Anchorage. These efforts, according to Greene, could assist raise awareness of excessive highs as a problem while also saving lives. But, for the time being, it’s crucial to recognize how many individuals are at risk—and how few of them are aware of it.