Global average temperatures continue to rise, with the last week seeing two of the hottest days on record, and the human toll from extreme heat is increasing year by year. In the United States, heat waves are now considered the deadliest weather-related natural disaster. However, experts agree that the number of deaths from heatstroke is greatly underestimated, as deaths from heatstroke can manifest as heart attacks, kidney failure, and other illnesses.
Earlier this year, the Federation of American Scientists called on the Centers for Disease Control and Prevention to upgrade and expand health tracking systems to more accurately reflect the true toll of heatwaves on human health, develop guidelines for states on reporting heatstroke deaths, and integrate environmental conditions with electronic health records.
Knowing how many people die from heat exposure each year would not only raise public awareness of the issue and save lives, but also ensure investments in heat prevention reflect the severity of the problem, says Christy Aebi, an epidemiologist at the University of Washington who has studied the impacts of climate change on human health for more than 30 years.
“I think it’s important to take a step back and realize that these deaths are preventable,” Ebi said in an interview. Yale Environment 360“People don’t need to die from the heat.”
Christy Ebi
University of Washington
Yale Environment 360: This summer is shaping up to be the hottest in U.S. history. You’ve been studying the issue of rising heatwave deaths, but do you know how many people are dying?
Christy Ebi: The number of excess deaths recorded on death certificates is much higher than reported, because many people died from heatstroke. However, this is only a small fraction of the total number of people who died during or immediately after a heatwave. Analysis of excess deaths after heatwaves has shown that about 50% of all deaths were due to cardiovascular disease.
The CDC estimates that about 1,200 Americans die from heatstroke each year, but that’s probably an underestimate by a factor of 10 or more. Estimates from a few years ago suggested that the actual number of deaths from heatstroke in the U.S. was between 10,000 and 12,000, but that number is likely much higher now.
360: No Why is there such a large discrepancy between the actual number of excess deaths and the number attributed to heat?
shrimp: Imagine two people who are taken to the emergency room with heart attacks. One had a heart attack caused by the heat, and the other did not. In the middle of a crisis, there is no way to determine at an individual level which heart attacks were exacerbated by the heat and which were not. In both cases, the cause of death would be recorded as a heart attack.
But at the population level, we know — as with COVID, if you look at the number of deaths in a given period and compare it to previous periods when there were no epidemics or heat waves, you get a relatively accurate number of excess deaths — but at the individual level, that attribution is pretty hard to determine.
“Heat is a silent killer… The first sign that people are in trouble is that they become confused and can’t determine what’s going on.”
360: No So is it more accurate to look at the number of excess deaths over a period of time than, say, looking at what a doctor writes on a death certificate?
shrimp: Yes. The focus of the emergency department is to save lives, so you don’t want to change that dynamic. But people die from kidney, respiratory, and a variety of other problems. Analyzing how heat has affected those illnesses is difficult at the individual level. But it’s relatively easy at the population level.
360: No Over the past few months, the Federation of American Scientists, which works to minimize the risks of major global threats, including climate change, has published several statement They are calling for the adoption of a standard methodology for measuring heatstroke deaths. Would that help?
shrimp: CDC is actively exploring this because it is acutely aware that current estimates of heatstroke mortality significantly underestimate the burden. The goals of understanding heatstroke fatalities include raising awareness and ensuring that investment levels reflect the magnitude of the problem.
While precision is required, achieving it comes with trade-offs: Investigating every death during a heatwave to determine which are heat-related requires resources and time, taking time away from other priority health issues.
Paramedics treat 66-year-old Deb Billet for symptoms of heat stroke on July 10, 2024 in Henderson, Nevada.
John Rocker/AP Photo
360: No Do we know how much excess deaths from heat waves have increased dramatically over the last decade or two?
shrimp: There are certainly studies of excess deaths, and climate change is causing more deaths in some places, but not in others, because people are adapting to the changes. And of course communities are adapting by putting in place early warning systems, by building cooling shelters, and by making other changes to protect their people.
360: No Do we know what percentage of heatstroke deaths are actually due to climate change?
shrimp: There is ample evidence – and extensive modelling – that heatwaves are increasing in frequency, intensity and duration. study A report published a few years ago looked at 43 countries and found that climate change was responsible for an average of 37 percent of summer heat-related mortality in those countries over the past few decades.
360: No You’ve said before that people don’t think of heat as something to worry about, but what you’ve just said suggests that that’s changing – that people are becoming more aware of the dangers of heat than they were a few years ago.
shrimp: And thanks to the media for reporting this story and helping people understand how much danger they are in. Heat is a silent killer. Early signs of heatstroke include nausea, fatigue and dizziness. But the first signs that people are in trouble can be hard to spot because they are often confused and unable to determine for themselves what is going on. That means we all need to pay attention to our family, friends and coworkers when the temperatures are high to make sure they are OK.
“Focusing on whether the future will be livable ignores human creativity.”
360: No People don’t usually die or have very severe reactions on the first day of a heatwave. Why is that?
shrimp: It has to do with core body temperature and how that temperature affects your cells and organs. It doesn’t happen instantly; it takes a while for your cells and organs to start responding to the high temperatures, so you’ll start to see the effects 24 hours after the heatwave begins.
360: No So far I’ve mostly talked about the United States, but in many parts of the world, heat is rising to levels that are life-threatening for people outdoors. Will entire countries soon enter uninhabitable territory?
shrimp: I think it’s important to take a step back and realize that these deaths are preventable and people don’t have to die from heat. Focusing on livability doesn’t take into account human ingenuity. We live in a variety of environments that are inhospitable. People live in Antarctica for several months a year. Humans have found ways to survive in very harsh conditions by improving infrastructure, clothing, and behavioral patterns. Of course, greenhouse gas emissions make it more complicated. So focusing on how to prevent these deaths is a priority from my perspective.
A rooftop garden at a school in Nanning, China.
Costfoto/NurPhoto via Getty Images
360: No What can we do now to design a world that can better withstand these heat waves?
shrimp: We need to have a heatwave plan with two main components: a heatwave early warning and response system that focuses on response. This goes beyond just telling people it’s hot. We need to tell people what they can do, ensure they have access to services, make sure there are cooling shelters, ensure outreach to people who are homeless, make sure people who work outside are protected, make sure aged care residents have access to cooling.
Another part of heat planning is long-term planning. What does our city look like in 30 to 50 years? Will white roofs be mandatory for everyone? Will green roofs be mandatory for buildings over a certain size? Are we planting trees that will cool our neighborhoods and survive a hotter future?
360: No So are you hopeful?
shrimp: I am fundamentally a anxious optimist.
360: No It’s understandable to be worried, but where is that optimism coming from?
shrimp: The optimism comes from the fact that our society is always changing and always progressing, and it also comes from my students, who really care about the problem of climate change and are passionate about helping to find even more solutions in the future.
This interview has been edited for length and clarity.
