The map of the Eastern United States has turned purple.
That’s the color used by the National Weather Service to distinguish the most severe category of extreme heat — a “rare and long-duration” event “with no overnight relief” — which spread like a bruise on Thursday morning from Chicago to Detroit and across the entire state of Ohio. From there, the purple splits north toward Toronto — where Portugal and Croatia will face each other tonight in a Round of 32 match — and down across the 13 original colonies, from Boston to New York City to Washington, D.C., Richmond, Charlotte, and Atlanta. An estimated 83 million Americans, or about a quarter of the population, are under the most extreme heat warning, with local temperatures cresting 100 degrees Fahrenheit; in many places, humidity will push the heat index up to 15 degrees higher.
That’s killer heat. Although the United States has a higher deployment of air conditioning than Europe, early tallies from the heat wave on the continent in late June found that some 20,000 people died from “heat-exacerbated causes” like heart attacks. In general, in New York City, an estimated 3% of deaths between May and September are due to the heat, a recent city report found — that’s about 500 deaths a year, close to the number of homicides during the city’s year of peak violence in 1990.
“Extreme heat is a chronic stressor that leads to hundreds of deaths in New York City,” Jeff Schlegelmilch, the director of the National Center for Disaster Preparedness at the Columbia Climate School, told me. “I’ve seen models showing the cumulative number of excess deaths over the next several decades could be in the tens of thousands.”
But while heat waves like the one this week bring much-needed attention to the public health crisis, it’s not actually extreme events that are driving those mortality figures. According to the city, about 80% of heat-related deaths in New York occur when temperatures are below 95 degrees Fahrenheit — that is, on hot, but not extremely hot, days. While risk increases with temperature in the way you’d expect, jumping sharply after 90 degrees Fahrenheit is crossed, there are more days in the still-dangerous 82- to 94-degree range on average each summer in New York (74, up from 52 in the 1970s) than extreme heat days like the ones occurring this week (of which there are about 11 per summer).
Schlegelmilch likened the moderate-temperature heat deaths to those during COVID, when it was the frontline workers who were paid hourly, couldn’t take days off, and who lived in more crowded homes who were the hardest hit. “We see those same patterns increasing exposure to heat,” he told me, noting that Latino and Black New Yorkers die from heat stress at rates two to three times higher, respectively, than white New Yorkers.
That said, the majority of people who die from heat-exacerbated causes do so in their homes, which “isn’t necessarily where the totality of the exposure to the heat is,” Schlegelmilch said. In fact, the number of people who die of direct heat stress in New York averages in the single digits per year, by comparison. “If you have to work outdoors, or you have to go back and forth to work and be exposed to the heat, and you go back into a home that is hot, and your body isn’t cooling off at night — this is actually something we’re very worried about tonight and tomorrow night — then the body doesn’t get that break.”
Part of the reason direct heat stress deaths are lower than those caused by chronic exposure is thanks to the agility, urgency, and attention of local governments, which issue heat warnings, promote cooling centers, and take preemptive measures during the worst heat waves — such as Toronto canceling its downtown World Cup watch party this afternoon. In New York this week, kiosks will help direct people to their nearest cooling centers, and local pools will stay open later. Meanwhile, to address more systemic heat impacts on the vulnerable, Mayor Zohran Mamdani has signed an executive order calling for the development and issuance of guidance for protecting outdoor workers and vendors during future heat events.
Because heat-related deaths often take the form of heart attacks, kidney disease, and diabetes, and therefore “don’t fit within the disaster declaration mechanisms” the same way floods or hurricanes do, “we don’t really have good policy to take care of this,” Schlegelmilch added. Particularly in cities with historically colder climates, such as Boston and New York, executive orders like Mamdani’s can be quick fixes, especially when followed by “lengthier and more thoughtful legislation and regulation.” But because the housing stock in such cities is older and, in some cases, even designed to retain heat, saving lives in the long term will require major infrastructure investments, ranging from tree planting to combat the urban heat island effect to expensive retrofitting.
“In the arc of history with disasters, we generally don’t do the things we need to do until it hurts too much,” Schlegelmilch said when I suggested that such a level of investment seems daunting, if not impossible, when spread out over the whole of New York, not to mention the Northeast. “It’s an open question how many people need to die, how many hours of productivity need to be lost, how much strain there is on infrastructure before everybody realizes this is not an abstract problem, that this is happening right now, and that it’s a hell of a lot more expensive to clean up after than to make these investments over the long run.”
An extreme heat wave might not be the primary driver of heat-related mortality in the United States, in other words, but it is certainly an opportunity to push for climate adaptation funding. “It’s not cheap at all,” Schlegelmilch agreed. “But it has to be part of the thinking, because there just isn’t another solution.”
