As extreme heat warnings are issued, experts warn of deadly consequences

As extreme heat is forecast across much of the U.S. this week, health departments across the country are warning people to take steps to survive the potentially deadly weather.

Extreme heat is the deadliest weather-related hazard in the U.S., claiming roughly 2,000 people annually, according to data from the Centers for Disease Control and Prevention (CDC). But experts note the official heat-related death toll may be undercounted due to heat sometimes not being considered as a factor in someone's death.

The latest CDC statistics show that 150 heat-related deaths have already occurred in the United States in 2025, but the data is only partially tabulated due to delays in reporting.

During the previous two years, more than 4,800 heat-related U.S. deaths were recorded, according to the CDC. Since 2020, there have been at least 9,436 heat-related deaths across the nation, the CDC noted.

The CDC statistics show that the number of heat-related deaths increased from 1,156 in 2020 to 2,415 in 2023, before slightly declining to 2,394 last year.

Meanwhile, the average number of heat waves that major U.S. cities experience each year has doubled since the 1980s, according to the federal government's Fifth National Climate Assessment.

An analysis by Climate Central, an independent group of scientists and communicators that research climate change, found that between June and August 2024, the average person experienced an additional 17 days of "risky heat" because of human-amplified climate change, and that over the summer months, one in four people on the planet had no respite from the heat.

The organization defined "risky heat" as days with temperatures hotter than 90% of the temperatures recorded in a local area from 1991 to 2020.

Heat waves are becoming even more dangerous as overnight temperatures are too high to relieve people from the heat, prolonging heat stress and the associated heat risks. Extreme levels of heat stress have more than doubled over the past 40 years, a trend that is expected to continue, according to NASA's Jet Propulsion Laboratory in Southern California.

Heat-related illnesses, like heat exhaustion or heat stroke, happen when the body cannot properly cool itself. While the body normally cools itself by sweating, during extreme heat, this might not be enough. In these cases, a person's body temperature rises faster than it can cool itself down and can cause damage to the brain and other vital organs.

Hot days can affect anyone. Those who are pregnant, with a heart condition or other chronic condition, as well as children with asthma, can be especially affected.

An estimated 70,000 people visit emergency rooms and an average of 10,000 are hospitalized annually due to heat.

Between Jan. 1, 2023, and Dec. 31, 2023, there were a total of 119,605 emergency room visits across the country for heat-related illnesses, with 92% of those visits occurring between May and September, according to a report published in April 2024 by the CDC.

July and August had higher than average ER visits due to heat than other warm-season months, including May, June and September, according to the report, which looked at data of ER visits caused by heat in 2023 and compared it to visits between 2018 and 2022. These findings are "consistent with record-breaking temperatures observed in 2023," the CDC said.

More than 200 million people across the country, from South Dakota to Florida and up the East Coast to Boston, are on alert for widespread, dangerous heat on Monday and into the new work week, and parts of the Southeast could experience the brunt of the sweltering conditions.

The highest temperatures on Monday will be focused in the Southeast, from the Carolinas to Florida, where extreme heat indices -- that is, what the temperatures feel like when humidity is factored in -- are forecast to be between 105 and 115 degrees.

Parts of Mississippi and Louisiana are on alert for heat indices up to 120 degrees.

Extreme heat is also expected to continue on Monday and Tuesday in the Midwest, where over the weekend temperatures felt between 97 to 111 degrees from Lincoln, Nebraska, up into Minneapolis.

The Northeast is in store for multiple days of dangerous heat. Heat indices in the Northeast are forecast to make it feel like the mid-90s to 104 on Monday.

Officials in Boston, Philadelphia, New York City and Washington, D.C., have all declared a heat emergency for this week, which includes opening cooling centers and working with utility providers to encourage energy conservation and maintain electrical grid reliability.

The New York City Emergency Management (NYCEM) and the Department of Health and Mental Hygiene are urging New Yorkers to take precautions to protect themselves from hot and humid weather that is expected to extend into Wednesday.

NYCEM Commissioner Zach Iscol said this will the fifth heat emergency for New York City this season.

"Prolonged heat like this is dangerous, especially for older adults, people with health conditions, and those without air conditioning," Iscol said in a statement. "Stay hydrated, limit outdoor activity, and find a Cool Option, whether it's a City cooling center like a library or a private space such as a friend's or relative's home."