Why summer heat is sending more Americans to the ER
Heat-related ER visit rates would have been 27% lower without human-caused warming, Climate Central estimates
A newly extended temperature record dating back to 1781 suggests Earth has warmed more than previously estimated, due to early greenhouse gas increases not captured in older data.
Human-caused warming is sending more Americans to emergency rooms for heat illness, according to a new Climate Central analysis that found climate change was linked to more than one in four heat-related emergency room visits nationwide.
The research examined ER visits during the warm seasons of 2018 through 2025. Researchers found that heat-related visit rates would have been about 27% lower without the added heat from human-caused warming, according to the study published in Climatic Change.
The deadliest heat event in the study was the June 2021 heat wave in the Pacific Northwest, when temperatures soared to levels many people in the region had never experienced.
People rest at the Oregon Convention Center cooling station in Oregon, Portland on June 28, 2021, as a heatwave moves over much of the United States. The village of Lytton in British Columbia broke the record for Canada's all-time high, with a temperature of 46.6 degrees Celsius (116 Fahrenheit), said Environment Canada. (Photo credit: KATHRYN ELSESSER/AFP via Getty Images)
It produced the highest daily rate of heat-related emergency room visits anywhere in the country during the eight-year study period. Researchers estimated that human-caused warming accounted for about 27% of that rate, according to the study.
The numbers became especially stark during a 10-day California heat wave. California recorded 1,911 heat-related emergency room visits from Aug. 31 through Sept. 9, 2022. Researchers estimated that about 570 of those visits were connected to human-caused warming.
“The data support what we are seeing in our hospitals: More people are getting sick from heat exposure, leading to interrupted work and school days, missed vacations, costly emergency department visits and hospitalizations, and, in some cases, death,” Dr. Caitlin Rublee, an emergency physician, told Climate Central.
Already hot days can become dangerous quickly
(Photo credit: Getty Images)
The study found that ER visits rose faster as daily high temperatures climbed. A few extra degrees on a hot day can push more people past the point where their bodies can safely cool themselves.
Heat illness can begin with headache, nausea, dizziness, weakness or heavy sweating. It can become life-threatening when the body’s temperature-control system fails, leading to confusion, seizures or unconsciousness, according to the Centers for Disease Control and Prevention.
The risk is not limited to people who work outdoors or exercise in the sun. A sweltering apartment, a long commute without air conditioning or a night without relief from the heat can also wear on the body.
Cities can make that problem worse. Pavement, rooftops and buildings absorb heat during the day then slowly release it after sunset. “So yes, cities are effectively adding their own layer of heat,” AccuWeather Meteorologist Brett Anderson said.
On clear nights with light winds, surrounding rural areas can cool much more quickly while dense urban neighborhoods hold onto the day’s heat, Anderson added. People without air conditioning may get little relief before the next hot day begins.
The study focused on daytime high temperatures and did not quantify the added effects of warm nights, humidity or prolonged heat waves, all of which can increase heat-related health risks.
Heat illness does not wait for peak summer
The most dangerous day of the year is not always in July or August.
In the Middle Atlantic, the highest rate of heat-related emergency room visits in 2022 occurred in May, the researchers found. Across much of the country, climate change accounted for its largest share of heat-related visits in September, when people may be less alert to heat risks.
That leaves plenty of room for people to get caught off guard: during a first early-season heat wave, a late-summer stretch when routines have resumed or a hot day that does not seem extreme enough to change plans.
Know when the heat has become an emergency
Older adults, young children, outdoor workers and people with certain health conditions face greater risks. So do people without a reliable place to cool down.
“We have an opportunity to prepare now and use science to guide action to prevent these illnesses and build more resilient health systems,” Rublee said.
(Photo credit: Getty Images)
During prolonged heat, move outdoor work, exercise and errands to cooler hours when possible. Drink water, take breaks in air conditioning and check on neighbors, relatives and anyone who may be struggling in the heat.
Heat exhaustion can look like headache, nausea, dizziness, weakness or heavy sweating. Get out of the heat, cool down and drink water before it progresses.
Confusion, slurred speech, fainting, seizures or loss of consciousness can signal heat stroke. Call 911 and begin cooling the person while help is on the way, the CDC advises.
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