This story is part of Record High, a Grist series examining extreme heat and its impact on how — and where — we live.

Extreme heat — summertime temperatures and humidity that exceed the historical average — is being made more frequent and intense by climate change. In the first two weeks of June, a late-spring hot spell prompted schools in the Northeast, Mid-Atlantic, and Great Lakes areas to close or send students home early. A heat wave broke temperature records in Puerto Rico — the heat index, a measure of how temperatures feel to the human body, reached 125 degrees Fahrenheit on parts of the island. And extreme heat spurred deadly storms and power outages for hundreds of thousands of customers from Texas to Louisiana.

All that heat is bad for human health and leads to a rise in hospitalizations for cardiovascular, kidney, and respiratory diseases, particularly among the urban poor, who often lack access to air conditioning and green spaces. Those hospitalizations will come with a hefty price tag. A new report from the public policy research group Center for American Progress estimates extreme heat will create $1 billion in health care-related costs in the United States this summer. The analysis, provided exclusively to Grist, projects that excessive heat will spur nearly 235,000 emergency department visits and more than 56,000 hospital admissions for conditions related to increased body temperature across the country this summer. 

“As the number of heat-event days increases, the probability that people are going to get rushed to the emergency room or get hospitalized increases,” said Steven Woolf, a senior fellow at the Center for American Progress, a professor of family medicine and population health at Virginia Commonwealth University School of Medicine, and a coauthor of the report. “We were interested in trying to quantify how big a risk that is.” 

Grist thanks its sponsors. Become one.

Woolf and a cohort of academics, scientists, and doctors from Virginia Commonwealth University analyzed health insurance claims in Virginia during the 80 extreme heat days that occurred in the state, on average, every summer from 2016 and 2020. The claims were filed for emergency room visits, hospital admissions, and other medical care. They used that data to determine how many Virginians sought a doctor’s help during these heat waves compared to other days. The authors tallied up “heat-related illnesses,” defined as including heat cramps, heat exhaustion, and heat stroke, as well as “heat-adjacent illness” — dehydration, rapid pulse, dizziness, or fainting. 

In Virginia, extreme heat spurred some 400 outpatient care visits for heat-related illness, 4,600 emergency room visits for heat-related or heat-adjacent illness, and 2,000 heat-related hospital admissions each summer. These are likely underestimates, the report’s authors noted, since many patients with higher body weight or organ diseases such as heart disease, for example, experience complications during heat waves that could be classified as heat-adjacent illnesses but are rarely formally diagnosed as such by their physicians. And many victims of extreme heat don’t seek medical care at all, which further obscures the true burden of heat-related illness. 

Grist thanks its sponsors. Become one.

The authors extrapolated from Virginia’s data to reach the conclusion that extreme heat will inflate health care costs across the nation by $1 billion every summer for the foreseeable future, an estimate Woolf said will probably shift as the breadth of research on this topic expands. The authors also found that the burden of extreme heat will be shouldered unequally by Americans. The costs will be felt most acutely in low-income and historically marginalized communities, where access to cooling resources such as air conditioning is patchy and green spaces are scarce. “People who live in nice neighborhoods, who have air-conditioned homes and tree-lined streets with plenty of shade,” Woolf said, “are protected from the heat in a way that doesn’t occur in a different part of town where there’s not much shade and people are less likely to either have air conditioning and fans or to have the resources to pay the electrical bills.” 

These inequities point to a slew of possible solutions, starting with a recognition on behalf of local and state governments that neighborhoods need to become more resilient to the effects of extreme heat. Many cities are already adapting to protect people from climate change, Woolf said, including using building and roofing materials that reflect heat, passing laws that subsidize power bills for low-income residents, and planting trees — a relatively low-cost intervention that is surprisingly effective at bringing down street-level temperatures. Local emergency management officials could also do a better job forecasting extreme heat so people have time to prepare, and public health officials could offer clearer communication about the symptoms of heat illness.

Justin S. Mankin, an assistant professor in Dartmouth University’s geography department who was not involved in this report and published a separate study last year on the economic impact of heatwaves in the U.S., acknowledged that the report is part of an essential effort to quantify the health care burden associated with extreme heat. But he said the methods the report’s authors used didn’t paint a complete picture, noting that a more comprehensive assessment of the economic toll of heat would have also accounted for the costs that pile up in the “weeks, months, and even years after an extreme event,” not only while the event is happening, as the report does. 

“I’d like to see more rigorous estimates of these costs using more sophisticated approaches,” he said. A more complete analysis would have looked at insurance claims from every state, instead of nationally extrapolating from Virginia’s data. The problem is that many states don’t have what’s called an all-claims database, which is a full and public accounting of all of the emergency room visits and hospitalizations that occur in a given year. “If we had that for all 50 states, we could do this analysis for the whole country,” Woolf said.

The report, Woolf noted, also doesn’t take the ways in which heat may affect businesses, infrastructure, schools, and other aspects of American life into account. He called for more research on this topic. “The collective implications of severe weather are really rather intimidating,” he said. “They just strengthen the arguments for us needing to do something about climate change and to be proactive about it.”

For more in-depth reporting on extreme heat, and the latest heat news, sign up for Grist’s new limited-run newsletter, Record High. The latest on extreme heat, delivered every Tuesday to your inbox. Subscribe here.